Delta Air Lines (DAL) 10-K2021 FY Annual report

UNITED STATES

Securities registered pursuant to Section 12(g) of the Act: None

Unless otherwise indicated or the context otherwise requires, the terms "Delta," "we," "us," and "our" refer to Delta Air Lines, Inc. and its subsidiaries.

FORWARD-LOOKING STATEMENTS

Statements in this Form 10-K (or otherwise made by us or on our behalf) that are not historical facts, including statements about our estimates, expectations, beliefs, intentions, projections or strategies for the future, may be "forward-looking statements" as defined in the Private Securities Litigation Reform Act of 1995. Forward-looking statements involve risks and uncertainties that could cause actual results to differ materially from historical experience or our present expectations. Known material risk factors applicable to Delta are described in "Risk Factors Relating to Delta" and "Risk Factors Relating to the Airline Industry" in "Item 1A. Risk Factors" of this Form 10-K, other than risks that could apply to any issuer or offering. All forward-looking statements speak only as of the date made, and we undertake no obligation to publicly update or revise any forward-looking statements to reflect events or circumstances that may arise after the date of this report.

Part I

As a global airline based in the U.S., we connect customers across our expansive global network. In 2019, prior to the onset of the COVID-19 pandemic, we served approximately 200 million customers and were the world’s largest airline by total revenues and the most profitable with five consecutive years of $5 billion or more in pre-tax income from 2015 through 2019. In 2020, we made significant adjustments to our network and operations as a result of the unprecedented and widespread impact of COVID-19 and the related travel restrictions and social distancing measures that significantly reduced demand for air travel.

We began restoring our network in 2021, as travel restrictions eased and vaccine programs became widespread both domestically and in international markets. As the year progressed, we saw a full return of domestic consumer travel to 2019 levels while business and international demand continued to lag. Despite this lag, business and international travel began to increase in the latter part of 2021, spurred in part by the U.S. government’s lifting of restrictions in November 2021 that prevented travelers from entering the United States from a number of specifically-identified countries.

In 2021, we continued to demonstrate agility, operational excellence and discipline. We believe that we are well positioned to manage the continued challenges brought by the pandemic, even when considering new variants spreading globally, continued uncertainty linked to the full return of business travel and evolving international travel restrictions. More information about the effect of the COVID-19 pandemic on our business and our recovery can be found in Item 7, Management's Discussion and Analysis of Financial Condition and Results of Operations.

Our internet address is www.delta.com. Information contained on our website is not part of, and is not incorporated by reference in, this Form 10-K.

We have five competitive advantages that support our trusted consumer brand, including our people and culture, our global network, our operational reliability, our customer loyalty and our financial foundation. Through the pandemic, we believe that we have strengthened our advantages and our brand. In 2021, we continued to have the world’s most valuable airline brand.

People and Culture

Our people are our strongest competitive advantage. Our employees provide world-class travel experiences for our customers while also giving back to the communities where they live, work and serve. Throughout the pandemic, we were able to avoid involuntary furloughs of U.S. employees by providing voluntary separation and early retirement programs, voluntary unpaid leaves and other initiatives. We have prioritized the health and safety of our employees by implementing an extensive employee COVID-19 testing program, partnering with Georgia to host the state’s largest COVID-19 vaccination site while steadily increasing the vaccination rate among our employees, providing pay protection programs for employees diagnosed with, exposed to or at high risk from COVID-19 and offering free flu shots for all U.S. employees. In February 2021, we hired a Chief Health Officer to reimagine our approach to health and well-being to accommodate the physical and mental health needs of our people. Delta was recognized by Glassdoor as one of its Best Places to Work for the sixth year in a row, ranking number 18 on the 2022 list of 100 large companies. The list is solely based on the input of employees who provide anonymous feedback on their daily jobs, benefits, interview experience and work environment. Being recognized on this list is a testament to Delta people and our culture.

Global Network

We and our alliance partners collectively serve over 130 countries and territories and over 800 destinations around the world. In 2019, prior to the onset of the COVID-19 pandemic, we offered more than 5,000 daily departures and as many as 15,000 affiliated departures including the premier SkyTeam alliance, of which Delta is a founding member. At the end of 2021, we offered more than 4,000 daily departures and approximately 5,500 affiliated departures as we began restoring our network.

Internationally, we have significant hubs and market presence in Amsterdam, London-Heathrow, Mexico City, Paris-Charles de Gaulle and Seoul-Incheon. As we continue our recovery from the impact of the COVID-19 pandemic, we expect to continue to evaluate and adjust our operations to address evolving conditions. Although our international operations have been substantially curtailed since March 2020 as a result of the COVID-19 pandemic, we have continued to serve Transatlantic, Transpacific and Latin America markets directly on Delta and through joint ventures with global airline partners. In 2021, we restored approximately 50% of capacity in international markets, but do not expect our international network to be fully restored to 2019 levels until 2023.

Through innovative alliances with Aeroméxico, Air France-KLM, China Eastern, Korean Air and Virgin Atlantic, and an alliance pending regulatory approval with LATAM Airlines Group S.A. (“LATAM ”), we seek to bring more choice to customers worldwide. Our strategic relationships with these international airlines are an important part of our business as they improve our access to markets around the world and enable us to provide customers a more seamless global travel experience across our alliance network. The most significant of these arrangements are commercial joint ventures that include joint sales and marketing coordination, co-location of airport facilities and other commercial cooperation arrangements. In some cases, we have reinforced strategic alliances through equity investments where we have opportunity to create deep relationships and maximize commercial cooperation. For additional information about the effect of the COVID-19 pandemic on our investments in these airlines, see Note 4 of the Notes to the Consolidated Financial Statements.

Our global network is supported by a fleet of approximately 1,200 aircraft as of December 31, 2021 that are varied in size and capabilities, giving us flexibility to adjust aircraft to the network. Prior to the pandemic, we began refreshing our fleet by acquiring new and more fuel efficient aircraft with increased premium seating to replace older aircraft, and had begun to reduce our fleet complexity with fewer fleet types. We accelerated this fleet simplification strategy by retiring 227 aircraft in 2020, with plans to retire additional aircraft by 2025, though we remain flexible and may decide to fly certain aircraft beyond their planned retirement date, to the extent supported by demand. Our new aircraft are on average 25% more fuel efficient per seat mile than retiring aircraft.

Operational Reliability

We remain committed to industry-leading reliability and are consistently among the industry’s best performers. In 2021, we had a system-wide completion factor of 99.4%, with 88.0% of our domestic flights arriving on time as reported to the U.S. Department of Transportation, both of which, based on preliminary data, are expected to exceed the performance of our U.S.-based peers. This reliability was a key component in Delta being named the Top U.S. Airline of 2021 by the Wall Street Journal in its annual airline scorecard rankings, which tracks seven important operations and customer metrics among nine U.S. airlines. This achievement recognizes the consistent efforts of our people to safely deliver reliable, on-time service while providing exceptional service.

Following the onset of the COVID-19 pandemic, we intensified our focus on ensuring the health and safety of our customers, including the creation of our industry-leading cleanliness standards through the Global Cleanliness organization and the implementation of the Delta CareStandard℠ to ensure a consistently safe and sanitized experience across our facilities and aircraft.

Customer Loyalty

Our SkyMiles program is designed to attract lifetime members and grow customer loyalty by offering incentives to increase travel with us. Our award-winning program offers a wide variety of benefits including award travel and access to complimentary elite benefits and services when traveling with us and our partners. As our brand has strengthened, the SkyMiles program has seen an acceleration in membership growth. We believe there is opportunity to continue this trend as we seek to elevate our customer engagement through opportunities to earn and redeem mileage credits (“miles”) as well as co-brand card offerings coupled with a strong customer experience. The SkyMiles program has a large, growing and premium membership base. This membership base has historically resulted in higher premium revenues and more resilient cash flows for us. SkyMiles has been widely recognized as a top loyalty program by external reviewers such as U.S. News and World Report and The Points Guy.

The SkyMiles program provides its members with the ability to earn miles when traveling on Delta, Delta Connection and our partner airlines. Miles may also be earned by using certain services offered by program partners, such as credit card companies, hotels, car rental agencies and ridesharing companies. To facilitate transactions with participating companies, we sell miles to non-airline businesses, customers and other airlines. Our most significant and valuable contract to sell miles relates to our co-brand credit card relationship with American Express. Miles may be used toward award redemptions such as flights and upgrades on Delta, our regional carriers and other participating airlines as well as donations with specific charities and more. In 2021, 10% of revenue miles flown on Delta were from award travel, as program members redeemed miles in the loyalty program for approximately 23 million award tickets.

Financial Foundation

In response to the effects of the COVID-19 pandemic, we raised significant amounts of liquidity in 2020 through the issuance of debt securities or through bilateral and syndicated secured and/or unsecured credit facilities and through the entry into sale-leaseback transactions. Our capital raising efforts were aided by the strength of our balance sheet prior to the pandemic. Restoring the strength of our balance sheet and reducing debt is a key financial priority. During 2021, we executed on our financial priority of stabilizing the business on the path to restoration and recovery. Since October 2020, we have made progress in restoring our balance sheet by reducing our debt by approximately $12 billion and voluntarily contributing $1.5 billion to our pension plans. We continue to be disciplined in managing non-fuel costs. We are efficiently rebuilding the airline, capturing fleet renewal benefits and driving operating leverage that we expect to produce a competitive cost structure. We expect that our unit revenue premium to the industry and competitive cost structure will support industry-leading margins and strong operating cash flow.

In addition to our competitive advantages, Delta continues to differentiate itself from the industry through expanded products, diversified revenue streams and investments in technology.

Our tickets are sold through various distribution channels, with 64% of tickets sold through direct channels in 2021. These include digital channels, such as delta.com and the Fly Delta app, and our reservations specialists where we deliver more direct, personalized interactions with our customers at reduced distribution costs. Indirect distribution channels include online travel agencies and traditional "brick and mortar" agencies. We make fare and product information widely available across those channels in an effort to ensure customers receive the best information and service options.

We continue to implement merchandising initiatives across our distribution channels to allow customers to better understand our product offerings, make it easier to buy the products they desire and increase customer satisfaction. This merchandising effort is most effective in Delta's digital channels where customers can compare all product options in a single, easy to understand display.

In recent years, we have diversified revenue streams beyond the basic sale of an airline ticket in an effort to reduce the impact of cyclicality and other reductions in air travel demand on our results. Our partnership with American Express provides us a co-brand revenue stream tied to broader consumer spending. Our continued focus on premium products and customer segmentation enhanced our revenue growth prior to the pandemic and reduced reliance on the most price sensitive customer segment, a differentiator that we believe has benefited us during the pandemic. We also maintain complementary portfolio businesses, such as our cargo business, which has grown significantly during the pandemic, and our Maintenance, Repair and Overhaul (“MRO”) operation, where we believe we remain well positioned for growth through contractual agreements with jet engine manufacturers.

Through our global network, our cargo operations are able to connect the world’s major freight gateways. We have historically generated cargo revenues in domestic and international markets through the use of cargo space on regularly scheduled passenger aircraft. In 2020, following the onset of the COVID-19 pandemic, reduced industry cargo capacity drove a significant increase in our cargo yield, and we also generated cargo revenue through the operation of cargo-only charter flights (i.e., using aircraft in our fleet not being utilized for passenger travel to fly cargo internationally). This trend continued in 2021, and we would expect capacity constraints and elevated market yields to continue through 2022 while the industry rebuilds international networks to pre-pandemic levels. We are a member of SkyTeam Cargo, an international airline cargo alliance with ten other airlines that offer a network spanning six continents, through which we provide global solutions to our customers by connecting our network with those partners.

We have various other businesses arising from our airline operations, including the following:

In 2021, the total revenue from our MRO operation and Delta Vacations was approximately $800 million.

Our objective is to make technology a strategic differentiator. We continue to invest in technological improvements that support our operations and provide tools for our employees. These investments include improvements to infrastructure and technology architecture to unify and improve access to data sources and continuing innovations to customer facing applications. We believe this digital transformation enhances interactions with our customers and allows our people to deliver more personalized service, further enhancing the customer experience and strengthening our brand.

Through the development of innovative new technologies, we can better serve customers and give our employees the best tools. For our customers, we are making investments in the digital platforms, in the airport and onboard our aircraft. We are evolving the Fly Delta app into a digital travel concierge for our customers to offer convenient services on the day of travel and deliver thoughtful notifications to make their travel journeys more seamless. In the airport, we are investing to create a smoother, less stressful and increasingly contactless travel experience. Onboard the aircraft, we continue to invest in in-flight entertainment with free messaging and improved Wi-Fi connectivity. As of December 31, 2021, approximately 95% of our mainline aircraft were equipped with seat-back screens. For our employees, we are investing in applications that allow our people to have more meaningful interactions with our customers, as well as tools to make our employees safer and better able to do their jobs.

We have marketing alliances with other airlines to enhance our access to domestic and international markets.

Each of our joint venture arrangements provides for joint commercial cooperation with the relevant partner within the geographic scope of the arrangement, including the sharing of revenues and/or profits and losses generated by the parties on the joint venture routes, as well as joint marketing and sales, coordinated pricing and revenue management, network and schedule planning and other coordinated activities with respect to the parties' operations on joint venture routes. Our implemented commercial joint ventures consist of the following:

In 2019, we entered into a framework agreement with LATAM to form a strategic alliance. Pursuant to that agreement, we acquired an approximately 20% equity stake in LATAM in January 2020 and made certain agreed-upon transition payments to LATAM. As part of our planned strategic alliance with LATAM, we also assumed 10 of LATAM’s A350 purchase commitments with Airbus S.A.S. for deliveries through 2025. In May 2020, we signed a trans-American joint venture agreement with LATAM that, subject to regulatory approvals, will combine our highly complementary route networks between North and South America, with the goal of providing customers a seamless travel experience and industry-leading connectivity. As a result of the COVID-19 pandemic, LATAM initiated a voluntary proceeding to reorganize under U.S. bankruptcy laws in which it has assumed the joint venture agreement. Upon, and subject to, completion of LATAM's restructuring process, we expect to acquire an approximately 10% equity stake in LATAM.

Regional Carriers

We have air service agreements with domestic regional air carriers that feed traffic to our route system by serving passengers primarily in small and medium-sized cities in the domestic market. These arrangements enable us to better match capacity with demand in these markets.

Our contractual agreements with regional carriers are primarily capacity purchase arrangements, under which we control the scheduling, pricing, reservations, ticketing and seat inventories for the regional carriers' flights operating under our "DL" designator code. We are entitled to all ticket, cargo, mail, in-flight and ancillary revenues associated with the flights under these capacity purchase arrangements. We pay those airlines an amount, as defined in the applicable agreement, which is based on a determination of their cost of operating those flights and other factors intended to approximate market rates for those services. These capacity purchase agreements are long-term agreements, usually with initial terms of at least ten years, which grant us the option to extend the initial term. Certain of these agreements provide us the right to terminate the entire agreement, or in some cases remove some of the aircraft from the scope of the agreement, for convenience at certain future dates.

SkyWest Airlines operates some flights for us under a revenue proration agreement. This proration agreement establishes a fixed dollar or percentage division of revenues for tickets sold to passengers traveling on connecting flight itineraries.

During 2021, we built on our previously announced plan to invest $1.0 billion through the end of 2030 toward airline carbon neutrality (the “$1.0 billion airline carbon neutrality goal”) by announcing our intention to set new climate goals that are aligned with the applicable framework of the Science Based Targets initiative (“SBTi”):

We have submitted both goals to SBTi for validation, but we are unable to predict the outcome of that process and when it will be completed.

The global aviation industry is viewed as a hard-to-abate sector, meaning it is innately difficult to decarbonize. We expect our path toward achievement of these ambitious climate goals to include the following levers, with the fleet and fuel levers expected to play the most significant roles:

These ambitious goals will require significant capital investment by Delta and third parties, government policies and incentives, research and development from manufacturers and other stakeholders and transformation of some of the world’s largest industries. Delta is committed to engaging our stakeholders and building coalitions to help drive down cost and increase production and consumption of alternative fuels and new technologies, and we recently hired the airline industry's only C-Suite level Chief Sustainability Officer to lead the continuing development of our climate strategy and transition plan. We have joined aviation industry-specific and broader coalitions in an effort to accelerate our climate goals and to influence climate and sustainability policy development. For example, within the aviation industry, Delta serves on the steering committee for Clean Skies for Tomorrow, which is focused on bringing SAF to scale faster by putting in place key processes and sending strong demand signals to the market.

As we connect people with communities, experiences and each other, we are committed to doing our part to build a better world. Giving back to the communities where we live, work and serve is part of our culture at Delta, and we focus our efforts in the community on four pillars of support: Environment, Equity, Education and Entire Well-being.

In 2021, Delta people continued to demonstrate their commitment to serving their community, even during a pandemic. Delta people donated 11,347 pints of blood, making Delta the No. 1 American Red Cross corporate blood drive sponsor for the fourth straight year. Our people helped build the 276th home built by Delta volunteers with Habitat for Humanity and built two playgrounds with The Trust for Public Land. Delta TechOps employees donated and assembled a record 1,250 bikes and collected 20 boxes of toys in partnership with Toys for Tots in addition to Delta’s $550,000 contribution to the organization to help make the holidays brighter for families in need.

As part of our commitment to equity, Delta launched a partnership with UNCF in 2021 to provide funding for their Emergency Student Aid program with a contribution of $500,000 dedicated to Degree Completion Aid and Emergency Retention Grants to assist students in need of emergency funding to be able to graduate. Delta also sponsors UNCF chapters in Atlanta, Boston, Detroit, Los Angeles, Minneapolis and New York.

Human Capital and Commitment to Diversity, Equity and Inclusion

We believe that Delta people are our strongest competitive advantage, and the high-quality service that they provide sets us apart from other airlines. As of December 31, 2021, we had approximately 83,000 full-time employee equivalents, of which approximately 81,000 were based in the U.S. In 2021, as our business began to recover from the impact of the COVID-19 pandemic, we hired approximately 11,000 new full-time employees across our business, including pilots, flight attendants, and gate and reservation agents.

Our principal human capital management objectives are to attract, retain and develop people who understand and are committed to delivering the “Delta Difference” that is core to our brand. To support these objectives, we have put in place programs that seek to:

The health and safety of our employees is foundational to achieving these objectives. We have long led the airline industry in employee safety and seek to achieve world-class personal safety performance. We have prioritized the health and safety of our employees by offering an extensive employee COVID-19 testing program, partnering with Georgia to host the state’s largest COVID-19 vaccination site while steadily increasing the vaccination rate among our employees, providing pay protection programs for employees diagnosed with, exposed to or at high risk from COVID-19 and offering free flu shots for all U.S. employees.

We believe that listening, engaging and connecting with employees furthers our human capital management objectives. We have historically done so primarily through our open-door policy, digital communication across all levels of the company, in-person events with senior management and company-wide and division-specific surveys to evaluate employee satisfaction. Since the onset of the pandemic, senior management has participated in regular company-wide town hall discussions with our employees and our senior executive leadership team has regularly shared memos with all employees regarding our ongoing commitment to our people and our culture. We have also continued to conduct periodic employee surveys to seek feedback on engagement levels in general, our well-being programs, diversity, equity and inclusion efforts and our culture of safety.

Collective Bargaining

We are in mediated discussions with the representative of the Delta pilots regarding terms of their amendable collective bargaining agreement under the auspices of the National Mediation Board ("NMB").

In addition to the domestic airline employee groups discussed above, approximately 180 refinery employees of our wholly owned subsidiary, Monroe Energy, LLC (“Monroe”) are represented by the United Steel Workers under an agreement that expires on February 28, 2022. This agreement is governed by the National Labor Relations Act ("NLRA"), which generally allows either party to engage in self-help upon the expiration of the agreement. Certain of our employees outside the U.S. are represented by unions, work councils or other local representative groups.

Labor unions periodically engage in organizing efforts to represent various groups of our employees, including at our operating subsidiaries, that are not represented for collective bargaining purposes.

Our results of operations are significantly impacted by changes in the price and availability of aircraft fuel. We purchase most of our aircraft fuel under contracts that establish the price based on various market indices and therefore do not provide material protection against price increases or assure the availability of our fuel supplies. We also purchase aircraft fuel on the spot market, from off-shore sources and under contracts that permit the refiners to set the price. We are currently able to obtain adequate supplies of aircraft fuel, including fuel produced by Monroe or procured through the exchange of gasoline, diesel and other refined petroleum products ("non-jet fuel products") the refinery produces, and crude oil for Monroe's operations.

The following table shows our aircraft fuel consumption and costs, which were materially reduced in 2020 and 2021 in large part due to our reduced operations in response to the COVID-19 pandemic.

Monroe Energy

Our Monroe subsidiaries operate the Trainer refinery and related logistics assets located near Philadelphia, Pennsylvania. The facilities include pipelines and terminal assets that allow the refinery to supply jet fuel to our airline operations throughout the Northeastern U.S., including our New York hubs at LaGuardia and JFK. These companies are distinct from us, operating under their own management teams and with their own boards. We own Monroe as part of our strategy to mitigate the cost of the refining margin reflected in the price of jet fuel, as well as to maintain sufficiency of supply to our New York operations.

Fuel Hedging Program

Our derivative contracts to hedge the financial risk from changing fuel prices are primarily related to Monroe’s inventory. We may utilize different contract and commodity types in this program and frequently test their economic effectiveness against our financial targets. We closely monitor the hedge portfolio and rebalance the portfolio based on market conditions, which may result in locking in gains or losses on hedge contracts prior to their settlement dates.

The airline industry is highly competitive, marked by significant competition with respect to routes, fares, schedules (both timing and frequency), operational reliability, services, products, customer service and loyalty programs. The industry has evolved through mergers and new entry, both domestically and internationally, and evolution in international alliances. Consolidation in the airline industry, the presence of subsidized government sponsored international carriers, changes in international alliances and the creation of immunized joint ventures have altered, and will continue to alter, the competitive landscape in the industry, resulting in the formation of airlines and alliances with significant financial resources, extensive global networks and competitive cost structures.

Domestic

Our domestic operations are subject to significant competition from traditional network carriers, including American Airlines and United Airlines, national point-to-point carriers, including Alaska Airlines, JetBlue Airways and Southwest Airlines, and other discount or ultra-low-cost carriers, including Spirit Airlines, Frontier Airlines and Allegiant Air, some of which may have lower costs than we do and provide service at low fares to destinations served by Delta. In particular, we face significant competition at our domestic hubs and key airports either directly at those airports or at the hubs of other airlines that are located in close proximity. We also face competition in smaller to medium-sized markets from regional jet operations of other carriers.

International

Our international operations are subject to competition from both foreign and domestic carriers, including from point-to-point carriers on certain international routes. Through alliance and other marketing and codesharing agreements with foreign carriers, U.S. carriers have increased their ability to sell international transportation, such as services to and beyond traditional European and Asian gateway cities. Similarly, foreign carriers have obtained increased access to interior U.S. passenger traffic beyond traditional U.S. gateway cities through these relationships.

In particular, several joint ventures among U.S. and foreign carriers, including several of our joint ventures as well as those of our competitors, have received grants of antitrust immunity allowing the participating carriers to coordinate schedules, pricing, sales and inventory. In addition, alliances formed by domestic and foreign carriers, including SkyTeam, the Star Alliance (among United Airlines, Lufthansa German Airlines, Air Canada and others) and the oneworld alliance (among American Airlines, British Airways, Qantas and others) have enhanced competition in international markets.

The DOT and the Federal Aviation Administration (the "FAA") exercise regulatory authority over air transportation in the U.S. The DOT has authority to issue certificates of public convenience and necessity required for airlines to provide air transportation. An air carrier that the DOT finds fit, willing, and able to perform the proposed service is given authority to operate domestic and international air transportation (including the carriage of passengers and cargo), as applicable. Since the passage of the Airline Industry Deregulation Act in 1978, airlines have generally been free to launch or terminate service to U.S airports without restriction, except with respect to certain slot-controlled and schedule-facilitated airports, as well as certain constraints related to service to small communities governed by the "Essential Air Services" program. The Coronavirus Aid, Relief, and Economic Security Act of 2020 (the "CARES Act") created certain continuation of service obligations in connection with the receipt of payroll support program funds by passenger airlines. Specifically, the DOT has the authority until March 1, 2022 to require airlines that received such funds to maintain scheduled air service deemed necessary to any point served by the airline before March 1, 2020. The DOT has issued several orders mandating such service, the most recent of which was finalized on April 29, 2021, mandating service levels through September 30, 2021, subject to certain definitions and exceptions as described in the order.

The DOT has jurisdiction over certain economic and consumer protection matters, such as unfair or deceptive practices and methods of competition, advertising, denied boarding compensation, baggage liability and disabled passenger transportation. The DOT also has authority to review certain joint venture agreements between domestic and international carriers. The DOT engages in regulation of economic matters such as transactions involving allocation of "slots" or similar regulatory mechanisms which limit the rights of carriers to conduct operations at airports where such mechanisms are in place. The FAA has primary responsibility for matters relating to the safety of air carrier flight operations, including airline operating certificates, control of navigable air space, flight personnel, aircraft certification and maintenance and other matters affecting air safety.

Authority to operate international routes and international codesharing arrangements is regulated by the DOT and by the governments of the foreign countries involved. International certificate authorities are also subject to the approval of the U.S. President for conformance with national defense and foreign policy objectives.

The Transportation Security Administration and the U.S. Customs and Border Protection, each a division of the Department of Homeland Security, are responsible for certain civil aviation security matters, including passenger and baggage screening at U.S. airports and international passenger prescreening prior to entry into or departure from the U.S.

Airlines are also subject to various other federal, state, local and foreign laws and regulations. For example, the U.S. Department of Justice has jurisdiction over some airline competition matters. The U.S. Postal Service has authority over certain aspects of the transportation of mail. Labor relations in the airline industry, as discussed below, are generally governed by the Railway Labor Act with oversight by the NMB. Environmental matters are regulated by various federal, state, local and foreign governmental entities. Privacy of passenger and employee data is regulated by domestic and foreign laws and regulations.

Fares and Rates

Airlines set ticket prices in all domestic and most international city-pairs with minimal governmental regulation, and the industry is characterized by significant price competition. Certain international fares and rates are subject to the jurisdiction of the DOT and the governments of the foreign countries involved. Many of our tickets are sold by travel agents, and fares are subject to commissions, overrides and discounts paid to travel agents, brokers and wholesalers.

Route Authority

Our flight operations are authorized by certificates of public convenience and necessity and also by exemptions and limited-entry frequency awards issued by the DOT. The requisite approvals of other governments for international operations are controlled by bilateral agreements (and a multilateral agreement in the case of the U.S. and the European Union) with, or permits or approvals issued by, foreign countries. Because international air transportation is governed by bilateral or other agreements between the U.S. and the foreign country or countries involved, changes in U.S. or foreign government aviation policies could result in the alteration or termination of such agreements, diminish the value of our international route authorities or otherwise affect our international operations. Bilateral agreements between the U.S. and various foreign countries that we serve are subject to renegotiation from time to time. The U.S. government has negotiated "Open Skies" agreements with many countries, which allow unrestricted access between the U.S. and these foreign markets.

Certain of our international route authorities are subject to periodic renewal requirements. We request extension of these authorities when and as appropriate. While the DOT usually renews temporary authorities on routes where the authorized carrier is providing a reasonable level of service, there is no assurance this practice will continue in general or with respect to a specific renewal. Dormant route authorities may not be renewed in some cases, especially where another U.S. carrier indicates a willingness to provide service.

Airport Access

Operations at three major domestic airports and certain foreign airports that we serve are regulated by governmental entities through allocations of "slots" or similar regulatory mechanisms. Each slot represents the authorization to land at or take off from the particular airport during a specified time period.

In the U.S., the FAA currently regulates the allocation of slots, slot exemptions, operating authorizations or similar capacity allocation mechanisms at Reagan National in Washington, D.C. and LaGuardia and JFK in the New York City area. Our operations at these airports generally require the allocation of slots or analogous regulatory authorizations. Similarly, our operations at London's Heathrow airport, Tokyo's Haneda airport and other international airports are regulated by local slot coordinators pursuant to the International Air Transport Association's Worldwide Scheduling Guidelines and applicable local law. We currently have sufficient slots or analogous authorizations to operate our existing flights, and we have generally been able to obtain the rights to expand our operations and to change our schedules. There is no assurance, however, that we will be able to do so in the future because, among other reasons, such allocations are subject to changes in governmental policies.

Airline Labor Regulation

In the U.S., airlines and labor unions are governed by the Railway Labor Act. Under the Railway Labor Act, a labor union seeking to represent an unrepresented craft or class of employees is required to file with the NMB an application alleging a representation dispute, along with authorization cards signed by at least 50% of the employees in that craft or class. The NMB then investigates the dispute and, if it finds the labor union has obtained a sufficient number of authorization cards, conducts an election to determine whether to certify the labor union as the collective bargaining representative of that craft or class. A labor union will be certified as the representative of the employees in a craft or class if more than 50% of votes cast are for representation. A certified labor union would then commence negotiations toward a collective bargaining agreement with the employer.

Under the Railway Labor Act, a collective bargaining agreement between an airline and a labor union does not expire, but instead becomes amendable as of a stated date. Either party may request that the NMB appoint a federal mediator to participate in the negotiations for a new or amended agreement. If no agreement is reached in mediation, the NMB may determine, at any time, that an impasse exists and offer binding arbitration. If either party rejects binding arbitration, a 30-day "cooling off" period begins. At the end of this 30-day period, the parties may engage in “self-help,” unless the U.S. President appoints a Presidential Emergency Board ("PEB") to investigate and report on the dispute. The appointment of a PEB maintains the "status quo" for an additional 60 days. If the parties do not reach agreement during this period, the parties may then engage in self-help. Self-help includes, among other things, a strike by the union or the imposition of proposed changes to the collective bargaining agreement by the airline. The U.S. Congress and the President have the authority to prevent self-help by enacting legislation that, among other things, imposes a settlement on the parties.

Environmental Regulation

We are also subject to certain environmental laws and contractual obligations governing the management and release of regulated substances, which may require the investigation and remediation of affected sites. Soil and/or ground water impacts have been identified at certain of our current or former leaseholds at several domestic airports. To address these impacts, we have a program in place to investigate and, if appropriate, remediate these sites. Although the ultimate outcome of these matters cannot be predicted with certainty, we believe that the resolution of these matters will not have a material adverse effect on our Consolidated Financial Statements.

The airline industry may face additional regulation of aircraft emissions in the U.S. and abroad and become subject to further taxes, charges or additional requirements to obtain permits or purchase allowances or emission credits for GHG emissions in various jurisdictions. For example, in 2021 the European Commission proposed legislation that could expand the reach of the EU ETS to include flights into and out of the EEA beginning in 2027 under certain circumstances, increase the stringency of the program, and establish a sustainable aviation fuel blending mandate for aviation fuel suppliers beginning in 2025, among other requirements. Individual EU member states have been developing their own requirements, including for example, a SAF mandate in France that will be phased in beginning in 2022. In the United States, various exploratory discussions continue around approaches to address climate change, such as carbon pricing, without a clear legislative path forward. Additional regulation could result in taxation, regulatory or permitting requirements from multiple jurisdictions for the same operations and significant costs for us and the airline industry. In addition to direct costs, such regulation could result in increased fuel costs passed through from fuel suppliers affected by any such regulations. Certain airports have also adopted, and others could in the future adopt, GHG emission or climate-related goals and requirements that could impact our operations or require us to make changes or investments in our infrastructure. We are monitoring and evaluating the potential impact of such developments.

Under the Energy Policy Act of 2005, as expanded by the Energy Independence and Security Act of 2007, the Renewable Fuel Standard ("RFS") was created, setting up specific targets of renewable fuel to be used in the U.S. economy by mandating the blending of renewable fuels into gasoline and on-road diesel ("Transportation Fuels"). Renewable Identification Numbers ("RINs") are assigned to renewable fuels produced by or imported into the U.S. that are blended into Transportation Fuels to demonstrate compliance with this obligation. A refinery may meet its obligation under RFS by blending the necessary volumes of renewable fuels with Transportation Fuels, by purchasing RINs in the open market or through a combination of blending and purchasing RINs. Because Monroe is able to blend only a small amount of renewable fuels, it must purchase the majority of its RINs requirement in the secondary market. Market prices for RINs have been volatile, marked by periods of sharp increases and decreases primarily in response to speculation about what the EPA and/or the U.S. Congress will do with respect to compliance obligations. In December 2021, the EPA issued proposed RFS volume requirements for 2020, 2021 and 2022, which are expected to be finalized in the first half of 2022. The EPA has not finalized the compliance deadlines to retire our obligations for 2020 and 2021, but we expect those deadlines to be within one year of the effective date of the new RFS volume requirements.

Civil Reserve Air Fleet Program

We participate in the Civil Reserve Air Fleet program (the "CRAF Program"), which permits the U.S. military to use the aircraft and crew resources of participating U.S. airlines during airlift emergencies, national emergencies or times of war. We have agreed to make available under the CRAF Program a portion of our international aircraft during the contract period ending September 30, 2022. The CRAF Program has only been activated three times since it was created in 1951, most recently in 2021 to support the military’s effort to evacuate people from Afghanistan following the withdrawal of U.S. troops from the country. Delta played a central role in transporting 10,000 Afghan refugees that were evacuated from Afghanistan and delivering needed supplies.

In addition to the other information set forth in this report, you should carefully consider the following material risk factors applicable to Delta. As described below, these risks could materially affect our business, financial condition or results of operations in the future.

The rapid spread of the COVID-19 virus, the continuing spread of its variants, the persistence of the resulting pandemic and measures implemented to combat it have had, and will continue to have, a material adverse effect on our business. It is possible that there will be future negative effects that we cannot presently predict, including near-term effects.

The rapid spread of the COVID-19 virus in 2020 and variants of the virus in 2021, the persistence of the resulting pandemic, the measures governments and private parties have implemented in order to stem the spread of this pandemic, and the general concern about the virus among travelers have had, and are continuing to have, a material adverse effect on the demand for worldwide air travel compared to historical levels, and consequently upon our business. Among other effects of the COVID-19 pandemic affecting air travel and our business:

These effects related to the COVID-19 pandemic have negatively impacted air travel in general, which in turn has materially adversely affected our revenues, results of operations and financial condition. Although vaccines have generally proved to be effective and certain of the restrictions above have been eased in some places, the ongoing pandemic, including large outbreaks, resurgences of COVID-19 in various regions and appearances of new variants of the virus, has resulted, and may continue to result, in their reinstitution. The effectiveness of vaccines against future variants that may develop is also unknown. Moreover, additional currently unknown restrictions or other events dissuading air travel may occur in the future as a result of an increase in COVID-19 case levels or other factors related to the pandemic (including possibly in the near term), lengthening the negative effects of the pandemic on our business.

Our operations have been, and could in the future be, negatively affected further if our employees are quarantined or sickened as a result of exposure to COVID-19, or if they are subject to additional governmental COVID-19 curfews or “shelter in place” health orders or similar restrictions. Measures restricting the ability of our airport or in-flight employees to come to work negatively impact our service or operations, all of which could negatively affect our business.

In response to the crisis, we took steps to mitigate the effects on our business, which themselves may have negative consequences with respect to our business and operations. For example, we took cost-saving actions to significantly reduce our capacity in 2020 but were not able to eliminate all costs related to unused capacity. Ultimately, cost-saving measures that we implemented to date, or may consider in the future, have not made up, and will not in the future make up, for the loss in revenue as a result of decreased ticket sales and cancellations. In addition, to protect the safety of our employees and customers, we have implemented significant additional cleaning measures on all of our aircraft and at the airports in which we operate which have increased our costs.

We are unable to predict how long conditions related to the pandemic will persist. The overall situation remains fluid, and it is impossible to predict the timing of future material developments and whether they will occur in the near, medium or long term. At this time, we are also not able to predict the extent to which the COVID-19 pandemic may result in permanent changes to our customers’ behavior, with such changes including but not limited to a permanent reduction in business travel as a result of increased usage of virtual meetings, and videoconferencing and teleconferencing products and more broadly, a general reluctance to travel, each of which could have a material impact on our business.

Collectively, the foregoing circumstances have had, and are continuing to have, a material adverse effect on our business, results of operations and financial condition. Future disease outbreaks or similar public health threats could have similar effects.

We have a significant amount of fixed obligations and incurred significant amounts of new debt in a short period in response to the COVID-19 pandemic. Insufficient liquidity may have a material adverse effect on our financial condition and business.

We have a significant amount of existing fixed obligations, including aircraft lease and debt financings, leases of airport property and other facilities, and other material cash obligations. In addition, we have substantial commitments for capital expenditures.

We had approximately $14.2 billion in cash, cash equivalents, short-term investments and aggregate principal amount committed and available to be drawn under our revolving credit facilities ("liquidity") as of December 31, 2021; however, our future liquidity could be negatively affected by the risk factors discussed in this Form 10-K, and in other filings we may make from time to time with the SEC. If our liquidity is materially diminished, we might not be able to timely pay our leases and debts or comply with certain financial covenants in our financing and credit card processing agreements or with other material provisions of our contractual obligations.

Agreements governing our debt, including our credit facilities and our SkyMiles financing agreements, include financial and other covenants. Certain of these covenants impose restrictions on our business, and failure to comply with any of the covenants in these agreements could result in events of default.

Our debt agreements contain various affirmative, negative and financial covenants, including our credit facilities and our SkyMiles financing agreements, each of which contains a minimum liquidity covenant. Certain of our debt agreements also contain collateral coverage ratios, and our SkyMiles financing agreements contain a debt service coverage ratio. A decline in these coverage ratios, including due to factors that are beyond our control, could require us to post additional collateral or trigger an early amortization event. Our SkyMiles financing agreements also restrict our ability to, among other things, change the policies and procedures of the SkyMiles program in a manner that would reasonably be expected to materially impair repayment of our SkyMiles debt.

Complying with certain of the covenants in our debt agreements and other restrictive covenants that may be contained in any future debt agreements could limit our ability to operate our business and to take advantage of business opportunities that are in our long-term interest. The terms of any future indebtedness we may incur could include more restrictive covenants.

While the covenants in our debt agreements are subject to important exceptions and qualifications, if we fail to comply with them and are unable to obtain a waiver or amendment, refinance the indebtedness subject to these covenants or take other mitigating actions, an event of default would result. These arrangements also contain other events of default customary for such financings. If an event of default were to occur, the lenders or noteholders could, among other things, declare outstanding amounts due and payable and where applicable and subject to the terms of relevant collateral agreements, repossess collateral, including aircraft or other valuable assets. In addition, an event of default or acceleration of indebtedness under one agreement could result in an event of default under other of our financing agreements. The acceleration of significant indebtedness could require us to seek to renegotiate, repay or refinance the obligations under our financing arrangements, and there is no assurance that such renegotiation or refinancing efforts would be successful.

We are at risk of losses and adverse publicity stemming from a serious accident involving our aircraft or aircraft of our airline partners.

An aircraft crash or other serious accident involving our aircraft or those of our airline partners could expose Delta to significant liability. Although we believe that our insurance coverage is appropriate, we may be forced to bear substantial losses from an accident in the event that the coverage was not sufficient.

In addition, any accident involving an aircraft that we operate or an aircraft that is operated by an airline that is one of our regional carriers or codeshare, alliance or joint venture partners could create a negative public perception about safety and reliability for aviation authorities and the public, which could harm our reputation, resulting in air travelers being reluctant to fly on our aircraft and therefore harm our business.

Breaches or lapses in the security of the technology systems we use and rely on and the data stored within them, as well as ever-evolving global privacy and security regulatory obligations, could have a material adverse effect on our business.

As a regular part of our ordinary business operations, we collect and store sensitive data, including information necessary for our operations, personal information of our passengers and employees and information of our business partners. The secure operation of the networks and systems on which this type of information is stored, processed and maintained is critical to our business operations and strategy.

Our information systems and those of our service providers are subject to an increasing threat of continually evolving cybersecurity risks, and the increase in work-from-home arrangements since the onset of the COVID-19 pandemic could potentially enhance these risks. We expect unauthorized parties to continue attempting to gain access to our systems or information, or those of our business partners and service providers, including through fraud or other means of deception, or introduction of malicious code, such as viruses, worms, Trojan horses and ransomware. If successful, these actions could cause harm to our computer systems or compromise data stored on our computer networks or those of our business partners and service providers. For example, we were notified in 2018 that a third-party vendor of chat services for Delta and other companies determined we had been involved in a cyber incident for a short period in 2017. We have incurred remedial, legal and other costs in connection with this incident but the costs were not material to our financial position or results of operations. Hardware or software we or our business partners or service providers develop, acquire or use in connection with our systems may contain defects that could unexpectedly compromise information security.

The methods used to obtain unauthorized access, disable or degrade service or sabotage systems are constantly evolving and may be difficult to anticipate or to detect for long periods of time. As a result of these types of risks and regular attacks on our systems, we regularly review and update procedures and processes to prevent and protect against unauthorized access to our systems and information and inadvertent misuse of data. In addition to continuously assessing risk and reviewing our procedures, processes and technologies, we continue to educate our people about these risks and to monitor, review and update the process and control requirements we expect third parties and vendors to leverage and implement for the protection of information regarding our customers, employees or business partners that is in their care. However, the constantly changing nature of the threats means that we may not be able to prevent all information security breaches or misuse of data.

The compromise of our or our business partners’ or service providers’ technology systems resulting in the loss, disclosure, misappropriation of, or access to, our information or that of our customers, employees or business partners could result in legal claims or proceedings, liability or regulatory penalties under laws protecting the privacy and security of personal information, disruption to our operations and damage to our reputation, any or all of which could adversely affect our business. The costs to remediate breaches and similar system compromises that do occur could be material. In addition, as cybercriminals become more sophisticated, the cost of proactive defensive measures continues to increase.

Disruptions of our information technology infrastructure could interfere with our operations, possibly having a material adverse effect on our business.

Disruptions in our information technology capability could result from a technology error or failure impacting our internal systems, whether hosted internally at our data centers or externally at third-party locations, or large scale external interruption in technology infrastructure support on which we depend, such as power, telecommunications or the internet. The operation of our technology systems and the use of related data may also be vulnerable to a variety of other sources of interruption, including natural disasters, terrorist attacks, computer viruses, hackers and other security issues. A significant individual, sustained or repeated failure of our information technology infrastructure, including third-party networks we utilize and on which we depend, could impact our operations and our customer service, result in increased costs and damage our reputation. While we have in place initiatives to prevent disruptions and disaster recovery plans and continue to invest in improvements to these initiatives and plans, we have previously experienced infrastructure disruptions and these measures may not be adequate to prevent a future business disruption and any material adverse financial and reputational consequences to our business as recent outages of large cloud providers whom we rely on has shown.

Failure of the technology we use to perform effectively could have a material adverse effect on our business.

We are dependent on technology initiatives and capabilities to provide customer service and operational effectiveness in order to compete in the current business environment. For example, substantially all of our tickets are issued to our customers as electronic tickets, and a growing number of our customers check in using our website, airport kiosks and our FlyDelta mobile application. We have made and continue to make significant investments in customer facing technology such as delta.com, the FlyDelta mobile application, in-flight wireless internet, check-in kiosks, customer service applications, application of biometric technology, airport information displays and related initiatives, including security for these initiatives. We are also investing in significant upgrades to technology infrastructure and other supporting systems and transitioning to cloud-based technologies. The performance, reliability and security of the technology we use are critical to our ability to serve customers. If this technology does not perform effectively, including as a result of the implementation or integration of new or upgraded technologies or systems, our business and operations would be negatively affected, which could be material.

Our commercial relationships with airlines in other parts of the world and the investments that we have in certain of those carriers may not produce the results or returns we expect.

An important part of our strategy to expand our global network has been to develop and expand strategic relationships with a number of airlines through joint ventures and other forms of cooperation and support, including equity investments. We expect to continue exploring ways to deepen our alliance relationships with other carriers as part of our global business strategy. These relationships and investments involve significant challenges and risks, including that they may not generate the expected financial results or that we may not realize a satisfactory return on our investment. We are dependent on these other carriers for significant aspects of our network in the regions in which they operate.

The COVID-19 pandemic has significantly impacted the operations of our airline partners and could adversely affect the expansion of strategic relationships in the future. These carriers have incurred significant financial losses as a result of the pandemic, and some have been or may be forced to seek protection under applicable bankruptcy laws. For example, following the onset of the pandemic, LATAM and Grupo Aeroméxico filed voluntary proceedings to reorganize under Chapter 11 of the United States bankruptcy code and Virgin Atlantic undertook a voluntary recapitalization process in the United Kingdom ("U.K.") and instituted ancillary proceedings in support of that process in the U.S. As discussed further in Note 4 of the Notes to the Consolidated Financial Statements, due to the effects of the COVID-19 pandemic, along with these actions, the carrying value of our equity investments in these three carriers has been reduced to, and remained, zero as of December 31, 2021. During the December 2021 quarter, we announced additional investments in each of these carriers, which with respect to LATAM and Grupo Aeroméxico, remain subject to completion of their respective reorganizations and related terms, conditions and approvals. If any airline partners that seek to restructure or recapitalize are unable to do so successfully or if our commercial arrangements with these partners are not maintained, any investments or other assets associated with those partners could become impaired, and our business and results of operations could be materially adversely affected.

A significant disruption in, or other problems with respect to, the operations or performance of third parties on which we rely, including third-party carriers, could have a material adverse effect on our business and results of operations.

We rely on the operations and performance of third parties in a number of areas that are important to our business, including third-party regional carriers, international alliance partners and ground operation providers at some airports. While we have agreements with certain of these third parties that define expected service performance, we do not have direct control over their operations. To the extent that the operations of a third party on which we rely is significantly disrupted, including as a result of the pandemic, or if these third parties experience significant performance issues (including failing to satisfy any applicable performance standards) or fail to meet any applicable compliance requirements, our revenue may be reduced, our expenses may be increased and our reputation may be harmed, any or all of which could result in a material adverse effect on our business and results of operations.

Some regional carriers, including our wholly-owned subsidiary, Endeavor, have faced a shortage of qualified pilots. If this shortage becomes more widespread, third-party regional carriers may not be able to comply with their obligations to us, and Endeavor may not be able to perform as expected, which could reduce our capacity (available seat miles) and revenue, resulting in a material adverse effect on our business and results of operations.

We may never realize the full value of our intangible assets or our long-lived assets, causing us to record impairments that may materially adversely affect our results of operations.

In accordance with applicable accounting standards, we are required to test our goodwill and other indefinite-lived intangible assets for impairment on an annual basis, or more frequently where there is an indication of impairment. In addition, we are required to test certain of our other assets for impairment where there is an indication that an asset may be impaired. During the fiscal year ended December 31, 2020, we recorded significant impairment and related charges related to acceleration of our fleet simplification strategy and the write-down of investments in certain airline partners, stemming from the impact of the COVID-19 pandemic.

We may be required to recognize losses in the future due to, among other factors, extreme fuel price volatility, tight credit markets, government regulatory changes, decline in the fair values of certain tangible or intangible assets, such as aircraft, route authorities, and airport slots, unfavorable trends in forecasted results of operations and cash flows and an uncertain economic environment, as well as other uncertainties. Further impairment charges could have a material adverse effect on our results of operations.

Our business is labor intensive, utilizing large numbers of pilots, flight attendants, aircraft maintenance technicians, ground support personnel and other personnel. As of December 31, 2021, 20% of our workforce, primarily pilots, was unionized. Relations between air carriers and labor unions in the United States are governed by the Railway Labor Act, which provides that a collective bargaining agreement between an airline and a labor union does not expire, but instead becomes amendable as of a stated date. The Railway Labor Act generally prohibits strikes or other types of self-help actions both before and after a collective bargaining agreement becomes amendable, unless and until the collective bargaining processes required by the Railway Labor Act have been exhausted. The collective bargaining agreement with our pilots became amendable on December 31, 2019 and we are in discussions with the representative of the pilots regarding terms of the agreement under the auspices of the NMB. Separately, the NLRA governs Monroe’s relations with the union representing their employees, which generally allows self help after a collective bargaining agreement expires.

If we or our subsidiaries are unable to reach agreement with any of our unionized work groups in future negotiations regarding the terms of their collective bargaining agreements or if additional segments of our workforce become unionized, we may be subject to work interruptions or stoppages, subject to the requirements of the Railway Labor Act or the NLRA, as the case may be. Strikes or labor disputes with our unionized employees may have a material adverse effect on our ability to conduct business. Likewise, if third-party regional carriers with which we have contract carrier agreements are unable to reach agreement with their unionized work groups in current or future negotiations regarding the terms of their collective bargaining agreements, those carriers may be subject to work interruptions or stoppages, subject to the requirements of the Railway Labor Act, which could have a material adverse effect on our operations.

Our results can fluctuate due to the effects of weather, natural disasters and seasonality.

Our results of operations are impacted by severe weather, natural disasters and seasonality. Severe weather conditions and natural disasters (or other environmental events) can significantly disrupt service and create air traffic control problems. These events decrease revenue and can also increase costs. In addition, increases in the frequency, severity or duration of thunderstorms, hurricanes, typhoons, floods or other severe weather events, including from changes in the global climate and rising global temperatures, could result in increases in delays and cancellations, turbulence-related injuries and fuel consumption to avoid such weather, any of which could result in loss of revenue and higher costs. In addition, demand for air travel is typically higher in the June and September quarters, particularly in our international markets, because there is more vacation travel during these periods than during the remainder of the year. The seasonal shifting of demand causes our financial results to vary on a seasonal basis. Because of fluctuations in our results from weather, natural disasters and seasonality, results of operations for a historical period are not necessarily indicative of results of operations for a future period and results of operations for an interim period are not necessarily indicative of results of operations for an entire year.

Our business and results of operations are dependent on the price of aircraft fuel. High fuel costs or cost increases, including in the cost of crude oil, could have a material adverse effect on our results of operations.

Our results of operations are significantly impacted by changes in the price of aircraft fuel. Over the last decade, fuel prices have been highly volatile and at times have increased substantially. From 2019 to 2021, our average annual fuel price per gallon, including the impact of fuel hedges, has varied from $1.64 to $2.02 with year to year variations ranging from a decrease of 19% to an increase of 23%.

We acquire a significant amount of jet fuel from Monroe and through strategic agreements associated with the refinery that Monroe has with third parties. The cost of the fuel we purchase under these arrangements remains subject to volatility in the cost of crude oil and jet fuel. In addition, we have historically purchased a significant amount of aircraft fuel in addition to what we obtain from Monroe. Our aircraft fuel purchase contracts alone do not provide material protection against price increases as these contracts typically establish the price based on industry standard market price indices.

The competitive nature of the airline industry may affect our ability to pass along rapidly increasing fuel costs to our customers. In addition, because passengers often purchase tickets well in advance of their travel, a significant rapid increase in fuel price may result in the fare charged not covering that increase. At times in the past, we often were not able to increase our fares to offset fully the effect of increases in fuel costs, and we may not be able to do so in the future.

Significant extended disruptions in the supply of aircraft fuel, including from Monroe, could have a material adverse effect on our operations and results of operations.

Weather-related events, natural disasters, political disruptions or disputes involving oil-producing countries, changes in governmental policy concerning aircraft fuel production, transportation or taxes, changes in refining capacity, environmental concerns and other unpredictable events may impact crude oil and fuel supply and could result in shortages in the future. Shortages in fuel supplies could have negative effects on our results of operations and financial condition.

The disruption or interruption of production at the refinery could have a negative impact on our ability to acquire jet fuel needed for our operations. Disruptions or interruptions of production at the refinery could result from various sources including a major accident or mechanical failure, interruption of supply or delivery of crude oil, work stoppages relating to organized labor issues, or damage from severe weather or other natural or man-made disasters, including acts of terrorism. If the refinery were to experience an interruption in operations, disruptions in fuel supplies could have negative effects on our results of operations and financial condition. In addition, the financial benefits from the operation of the refinery could be materially adversely affected (to the extent not recoverable through insurance) because of lost production and repair costs.

If Monroe's cost of producing non-jet fuel products exceeds the value it receives for those products, the financial benefits we expect to achieve through the ownership of the refinery and our consolidated results of operations could be materially adversely affected.

An environmental or other incident associated with the operation of the Monroe refinery could have a material adverse effect on our consolidated financial results if insurance is unable to cover a significant liability. In addition, such an incident could damage our reputation.

Monroe's refining operations are subject to various hazards unique to refinery operations, including explosions, fires, toxic emissions and natural catastrophes. Monroe could incur substantial losses, including cleanup costs, fines and other sanctions and third-party claims, and its operations could be interrupted, as a result of such an incident. Monroe's insurance coverage does not cover all potential losses, costs or liabilities, and Monroe could suffer losses for uninsurable or uninsured risks or in amounts greater than its insurance coverage. In addition, Monroe's ability to obtain and maintain adequate insurance may be affected by conditions in the insurance market over which it has no control. If Monroe were to incur a significant liability for which it is not fully insured or for which insurance companies do not or are unable to provide coverage, this could have a material adverse effect on our consolidated financial results of operations or consolidated financial position. In addition, because of our ownership of Monroe, the occurrence of an environmental or other incident could result in damage to our reputation, which could have a material adverse effect on our financial results.

The operation of the refinery by Monroe is subject to significant environmental regulation. Failure to comply with environmental regulations or the enactment of additional regulation applicable to Monroe could have a material adverse effect on our consolidated financial results.

Monroe’s operations are subject to extensive environmental, health and safety laws and regulations, including those relating to the discharge of materials into the environment, waste management, pollution prevention measures and greenhouse gas emissions, which are subject to change over time. Monroe could incur fines and other sanctions, cleanup costs and third-party claims as a result of violations of or liabilities under environmental, health and safety requirements, which if significant, could have a material adverse effect on our consolidated financial results. In addition, the enactment of new, more stringent environmental laws and regulations, including any laws or regulations relating to greenhouse gas emissions, could significantly increase the level of expenditures required for Monroe or restrict its operations.

In particular, under the Energy Independence and Security Act of 2007, the EPA has adopted RFS that mandates the blending of renewable fuels into Transportation Fuels. RINs are assigned to renewable fuels produced or imported into the U.S. that are blended into Transportation Fuels to demonstrate compliance with this obligation. A refinery may meet its obligation under RFS by blending the necessary volumes of renewable fuels with Transportation Fuels, by purchasing RINs in the open market or through a combination of blending and purchasing RINs.

Existing laws or regulations could change, and the minimum volumes of renewable fuels that must be blended with refined petroleum products may increase. Increases in the volume of renewable fuels that must be blended into Monroe’s products could limit the refinery’s production if sufficient numbers of RINs are not available for purchase or relief from this requirement is not obtained, which could have a material adverse effect on our consolidated financial results.

If we lose senior management and other key employees and they are not replaced by individuals with comparable skills, or we otherwise fail to maintain our company culture, our business and results of operations could be materially adversely affected.

Significant damage to our reputation and brand, including as a result of significant adverse publicity or inability to achieve certain sustainability goals, could materially adversely affect our business and financial results.

Maintaining our reputation and global brand is critical to our business. We operate in a highly visible and public environment with significant real-time exposure to traditional and social media. Adverse publicity, whether justified or not, can rapidly spread, including through social or digital media. In particular, passengers can use social media to portray interactions with Delta, without context, in a manner that can be quickly and broadly disseminated. To the extent we are unable to respond in a timely and appropriate manner to adverse publicity, our brand and reputation may be damaged.

Our reputation and brand could also be adversely impacted by, among other things, failure to make progress toward and achieve our environmental sustainability and diversity, equity and inclusion goals, as well as public pressure from investors or policy groups to change our policies or negative public perception of the environmental impact of air travel. For example, we intend to invest $1.0 billion through 2030 toward airline carbon neutrality and to establish ambitious new medium- and long-term goals to reduce our emissions, but we are unable to achieve the latter goals using our existing fleet, current technologies and available fuel sources. We are diligently working to establish a reasonable transition plan with respect to our medium- and long-term climate goals; however, our ability to execute on such a plan is subject to substantial risks and uncertainties, as it is dependent on the actions of governments and third parties and will require, among other things, significant capital investment, including from third parties, research and development from manufacturers and other stakeholders, along with government policies and incentives to reduce the cost, and incent production, of SAF and other technologies that are not presently in existence or available at scale. Significant damage to our reputation and brand could have a material adverse effect on our business and financial results, including as a result of litigation related to any of these matters.

Terrorist attacks, geopolitical conflict or security events may adversely affect our business, financial condition and results of operations.

Terrorist attacks, geopolitical conflict or security events, or the fear or threat of any of these events, could have a significant adverse effect on our business. Despite significant security measures at airports and airlines, the airline industry remains a high profile target for terrorist groups. We rely on government provided threat intelligence and utilize private sources to constantly monitor for threats from terrorist groups and individuals, including from violent extremists both internationally and domestically, with respect to direct threats against our operations and in ways not directly related to the airline industry. In addition, the impact on our operations of avoiding areas of the world, including airspace, in which there are geopolitical conflicts and the targeting of commercial aircraft by parties to those conflicts can be significant. Security events, primarily from external sources but also from potential insider threats, also pose a significant risk to our passenger and cargo operations. These events could include random acts of violence and could occur in public areas that we cannot control.

Terrorist attacks, geopolitical conflict or security events, or the fear or threat of any of these events, even if not made directly on or involving the airline industry, could have a significant negative impact on us by discouraging passengers from flying, leading to decreased ticket sales and increased refunds. In addition, potential costs from these types of events include increased security costs, impacts from avoiding flight paths over areas in which conflict is occurring or could occur, such as flight redirections or cancellations, reputational harm and other costs. If any or all of these types of events occur, they could have a material adverse effect on our business, financial condition and results of operations.

The global airline industry is highly competitive and, if we cannot successfully compete in the marketplace, our business, financial condition and results of operations will be materially adversely affected.

The airline industry is highly competitive, marked by significant competition with respect to routes, fares, schedules (both timing and frequency), operational reliability, services, products, customer service and loyalty programs. Consolidation in the airline industry, changes in international alliances, the creation of immunized joint ventures and the rise of subsidized government-sponsored international carriers have altered and will continue to alter the competitive landscape in the industry, resulting in the formation of airlines and alliances with increased financial resources, more extensive global networks and competitive cost structures.

Our domestic operations are subject to significant competition from traditional network carriers, including American Airlines and United Airlines, national point-to-point carriers, including Alaska Airlines, JetBlue Airways and Southwest Airlines, and other discount or ultra-low-cost carriers, including Spirit Airlines, Frontier Airlines and Allegiant Air, some of which may have lower costs than we do and provide service at low fares to destinations served by Delta. In particular, we face significant competition at our domestic hubs and key airports either directly at those airports or at the hubs of other airlines that are located in close proximity. We also face competition in smaller to medium-sized markets from regional jet operations of other carriers. Our ability to compete in the domestic market effectively depends, in part, on our ability to maintain a competitive cost structure. If we cannot maintain our costs at a competitive level, then our business, financial condition and results of operations could be materially adversely affected.

Our international operations are subject to competition from both foreign and domestic carriers, including from point-to-point carriers on certain international routes. Through alliance and other marketing and codesharing agreements with foreign carriers, U.S. carriers have increased their ability to sell international transportation, such as services to and beyond traditional European and Asian gateway cities. Similarly, foreign carriers have obtained increased access to interior U.S. passenger traffic beyond traditional U.S. gateway cities through these relationships.

In particular, several joint ventures among U.S. and foreign carriers, including several of our joint ventures as well as those of our competitors, have received grants of antitrust immunity allowing the participating carriers to coordinate schedules, pricing, sales and inventory. In addition, alliances formed by domestic and foreign carriers, including SkyTeam, the Star Alliance (among United Airlines, Lufthansa German Airlines, Air Canada and others) and the oneworld alliance (among American Airlines, British Airways, Qantas and others) have enhanced competition in international markets.

The airline industry also faces competition from surface transportation and technological alternatives such as virtual meetings, teleconferencing or videoconferencing, and the intensity of this competition has likely increased, at least in the near term, as a result of the COVID-19 pandemic. Increased competition in both the domestic and international markets may have a material adverse effect on our business, financial condition and results of operations.

Extended interruptions or disruptions in service at major airports in which we operate or significant problems associated with a type of aircraft or engine we operate could have a material adverse effect on our operations.

The airline industry is heavily dependent on business models that concentrate operations in major airports in the United States and throughout the world. An extended interruption or disruption at an airport where we have significant operations, whether resulting from a discrete event, such as a hurricane, or the manifestation of a chronic physical risk, such as rising sea levels, could have a material adverse effect on our business, financial condition and results of operations.

Similarly, the airline industry is heavily dependent on a limited number of aircraft and engine manufacturers whose products are subject to extensive regulatory requirements. Any significant problems associated with an aircraft or engine type that we operate, such as design defects, mechanical problems, contractual performance by the manufacturers or adverse perception by the public leading to customer avoidance or adverse actions by the FAA resulting in grounding could have a negative impact on our operations if we are not able to substitute or replace the affected aircraft or engine type and could, in any event, have a material adverse effect on our financial condition and results of operations.

The airline industry is subject to extensive government regulation, which is costly and could materially adversely affect our business.

Airlines are subject to extensive regulatory and legal compliance requirements that result in significant costs and may have material adverse effects on our business. For instance, the FAA from time to time issues directives and other regulations relating to the maintenance and operation of aircraft that necessitate significant expenditures and could carry operational implications. We expect to continue incurring significant expenses to comply with the FAA’s regulations. In addition, a directive or other regulation that has a significant operational impact on us could have a material adverse impact on our financial results.

Other laws, regulations, taxes and airport rates and charges have also been imposed from time to time that significantly increase the cost of airline operations, reduce revenues or otherwise impact our business. The industry is heavily taxed. Additional taxes and fees, if implemented, could negatively impact our results of operations.

Airport slot access is subject to government regulation and changes in slot regulations or allocations could impose a significant cost on the airlines operating in airports subject to such regulations or allocations or otherwise adversely affect an airline’s business. Certain of our hubs are among the most congested airports in the United States and have been, and could in the future be, the subject of regulatory action that might limit the number of flights and/or increase costs of operations at certain times or throughout the day. Air traffic control inefficiencies can also enhance these pressures.

In addition, the failure of the federal government to upgrade the U.S. air traffic control system, which is regulated by the FAA, has resulted in delays and disruptions of air traffic during peak travel periods in certain congested markets. The failure to improve the air traffic control system could lead to increased delays and inefficiencies in flight operations as demand for U.S. air travel increases, having a material adverse effect on our operations. Failure to update the air traffic control system in a timely manner, and the substantial funding requirements of an updated system that may be imposed on air carriers, may have an adverse impact on our financial condition and results of operations.

As an international carrier, we are subject to a wide variety of U.S. and foreign laws that affect trade, including tariff and trade policies, export and import requirements, taxes, monetary policies and other restrictions and charges. In particular, the imposition of significant tariffs with respect to aircraft that we are not able to mitigate could substantially increase our costs, which in turn could have a material adverse effect on our financial results.

In addition, some of our operations are in high-risk legal compliance environments. Failure to comply with trade sanctions and restrictions, the Foreign Corrupt Practices Act (the "FCPA") and similar anti-bribery laws in non-U.S. jurisdictions, as well as other applicable laws or regulations could result in litigation, assessment of damages, imposition of penalties or other consequences, any or all of which could harm our reputation and have an adverse effect on our financial results. In certain circumstances, we also may be subject to consequences of the failure of our airline partners to comply with laws and regulations, including U.S. laws to which they may be subject such as the FCPA.

We and other U.S. carriers are subject to U.S. and foreign laws regarding privacy of passenger and employee data that are not consistent in all countries in which we operate and which are continuously evolving, requiring ongoing monitoring and updates to our privacy and information security programs. Although we dedicate significant resources to manage compliance with global privacy and information security obligations, this challenging regulatory environment may pose material risks to our business, including increased operational burdens and costs, regulatory enforcement, and legal claims or proceedings.

The airline industry is subject to many forms of environmental regulation, including but not limited to increased regulation to reduce emissions and other risks associated with climate change. The cost of compliance with more stringent environmental regulations, failure to comply with existing or future regulations or failure to otherwise manage the risks of climate change effectively could have a material adverse effect on our business.

Many aspects of our operations are subject to evolving and increasingly stringent federal, state, local and international laws governing the protection of the environment. Compliance with existing and future environmental laws and regulations could require capital investment and increase operational costs, and violations can lead to significant fines and penalties and reputational harm.

Future regulatory action concerning climate change, aircraft emissions and noise emissions could have a significant effect on the airline industry. In order to address aircraft carbon dioxide emissions, the International Civil Aviation Organization, a United Nations specialized agency, formally adopted a global, market-based emission offset program known as CORSIA. This program establishes a goal for the aviation industry to achieve carbon-neutral growth in international aviation beginning in 2021 through the use of carbon offsets and/or lower carbon aviation fuel. The baseline for establishing airlines’ offset obligations under CORSIA was originally set as an average of 2019 and 2020 emissions. However, given the COVID-19 pandemic and resulting unprecedented reduction in international travel, ICAO removed 2020 from the baseline calculation for the first phases of CORSIA, from 2021 to 2027. ICAO has yet to decide how to apply the baseline beyond 2027. Some countries and other stakeholders, however, have advocated for reestablishing 2020 in the baseline and for using 2020 for the future baseline calculation, which, if adopted, would significantly increase the airline industry’s projected obligations under the program and the cost of compliance. Certain CORSIA program details remain to be developed and could potentially be affected by political developments in participating countries or the results of the pilot phase of the program, and thus the impact of CORSIA cannot be predicted at this time. However, CORSIA is expected to increase operating costs for airlines that operate internationally.

In addition to CORSIA, we may face a patchwork of regulation of aircraft emissions in the U.S. and abroad and could become subject to further taxes, charges or additional requirements to obtain permits or purchase allowances or emission credits for greenhouse gas emissions in various jurisdictions. For example, in 2021 the European Commission proposed legislation that would expand the reach of the EU ETS to include flights into and out of the European Economic Area beginning in 2027 under certain circumstances, increase the stringency of the program, and establish a sustainable aviation fuel blending mandate for aviation fuel suppliers, among other requirements. Individual EU member states have been developing their own requirements, including for example, a SAF mandate in France that will be phased in at the beginning of 2022. In the United States various exploratory discussions continue around approaches to address climate change, such as carbon pricing, without a clear legislative path forward. Additional regulation could result in taxation, regulatory or permitting requirements from multiple jurisdictions for the same operations and significant costs for the airline industry, including Delta. In addition to direct costs, such regulation could result in increased fuel costs passed through from fuel suppliers affected by any such regulations. While the specific nature of future actions is hard to predict, new laws or regulations related to environmental matters adopted in the U.S. or other countries could impose significant additional costs on or otherwise adversely affect our operations. Certain airports have also adopted, and others could in the future adopt, greenhouse gas emission or climate-related goals and requirements that could impact our operations or require us to make changes or investments in our infrastructure.

In addition to risks from potential changes to environmental regulation and policy, the transition to lower-carbon technologies, such as SAF, or changes in consumer preferences resulting from a negative perception of the environmental impact of air travel could materially adversely affect our business and financial results. For example, lower-carbon technologies such as SAF and direct air capture technologies are currently not available at scale and may take decades to develop, and the cost to transition to them could be prohibitively expensive without appropriate government policies and incentives in place. As more businesses have publicly announced environmental sustainability goals, the cost of carbon offsets has also increased significantly and will likely continue to do so.

Because of the global nature of our business, unfavorable economic or political conditions in the markets in which we operate or volatility in currency exchange rates could have a material adverse effect on our business, financial condition and results of operations.

As a result of the discretionary nature of air travel, the airline industry has been cyclical and particularly sensitive to changes in economic conditions. Because we operate globally, our business is subject to economic and political conditions throughout the world. During periods of unfavorable or volatile economic conditions in the economy in the U.S. or abroad, including as a result of the COVID-19 pandemic and the worldwide response to it, demand for air travel can be significantly impacted as business and leisure travelers choose not to travel, seek alternative forms of transportation for short trips or conduct business using technological alternatives. If unfavorable economic conditions occur, particularly for an extended period, our business, financial condition and results of operations may be adversely affected. In addition, significant or volatile changes in exchange rates between the U.S. dollar and other currencies, and the imposition of exchange controls or other currency restrictions, may have a material adverse effect on our liquidity, financial conditions and results of operations.

Our international operations are an important part of our route network. Political disruptions and instability around the world can negatively impact the demand and network availability for air travel. Additionally, any deterioration in global trade relations, such as increased tariffs or other trade barriers, could result in a decrease in the demand for international air travel.

None.

Our operating aircraft fleet, purchase commitments and options at December 31, 2021 are summarized in the following table. We have been experiencing a recovery in demand from the COVID-19 pandemic, which has led to an increase in our capacity and utilization of our aircraft compared to the year ended December 31, 2020. Accordingly, as of December 31, 2021, all aircraft in our operating fleet are reflected in the table below compared to approximately 10% that were temporarily parked as of December 31, 2020. See Note 15 of the Notes to the Consolidated Financial Statements for additional information on the restructuring charges recorded in 2020 related to our fleet retirement plans.

The following table summarizes the aircraft operated by regional carriers on our behalf at December 31, 2021.

Aircraft Purchase Commitments

As part of a multi-year effort, we have been investing in new aircraft to provide an improved customer experience, greater fuel efficiency and thus reduced carbon emissions, better operating economics and more premium products. Our purchase commitments for additional aircraft at December 31, 2021 are detailed in the following table:

Airline Operations

We lease most of the land and buildings that we occupy. Our largest aircraft maintenance base, various equipment maintenance, cargo, flight kitchen and training facilities and most of our principal offices are located at or near the Atlanta airport on land leased from the City of Atlanta. We lease ticket counters, gate areas, operating facilities and other terminal space in most of the airports that we serve. At most airports, we have entered into use agreements which provide for the non-exclusive use of runways, taxiways and other improvements and facilities; landing fees under these agreements normally are based on the number of landings and weight of aircraft. These leases and use agreements generally run for periods of less than one year to 30 years or more, and often contain provisions for periodic adjustments of lease rates, landing fees and other charges applicable under that type of agreement. We also lease aircraft maintenance, equipment maintenance and air cargo facilities at several airports. Our facility leases generally require us to pay the cost of providing, operating and maintaining such facilities, including, in some cases, amounts necessary to pay debt service on special facility bonds issued to finance their construction. We also lease computer facilities, marketing offices, reservations offices and other off-airport facilities in certain locations for varying terms.

We own our Atlanta reservations center, other real property in Atlanta and reservations centers in Minot, North Dakota and Chisholm, Minnesota.

Refinery Operations

Our Monroe subsidiaries own and operate the Trainer refinery and related assets in Pennsylvania. The facilities include pipelines and terminal assets that allow the refinery to supply jet fuel to our airline operations throughout the Northeastern U.S., including our New York hubs at LaGuardia and JFK.

In July 2015, a number of purported class action antitrust lawsuits were filed alleging that Delta, American, United and Southwest had conspired to restrain capacity. The lawsuits were filed in the wake of media reports that the U.S. Department of Justice had served civil investigative demands upon these carriers seeking documents and information relating to this subject. The lawsuits have been consolidated into a single Multi-District Litigation proceeding in the U.S. District Court for the District of Columbia. We believe the claims in these cases are without merit and vigorously defended these lawsuits. Our summary judgment motion has been fully briefed and pending since May 2021.

Not applicable.

Part II

Our common stock is listed on the New York Stock Exchange ("NYSE") under the trading symbol DAL.

As of January 31, 2022, there were approximately 2,300 holders of record of our common stock.

We made cash dividend payments of $980 million during the year ended December 31, 2019 and $260 million in the March 2020 quarter prior to the COVID-19 pandemic. In March 2020, we suspended dividends due to the impact of the COVID-19 pandemic. The CARES Act and payroll support program extensions restrict the payment of dividends through September 2022. Dividend payments beyond that time will be dependent upon our results of operations, financial condition, cash requirements, future prospects and other factors deemed relevant by the Board of Directors.

The following graph compares the cumulative total returns during the period from December 31, 2016 to December 31, 2021 of our common stock to the Standard & Poor's 500 Stock Index and the NYSE ARCA Airline Index. The comparison assumes $100 was invested on December 31, 2016 in each of our common stock and the indices and assumes that all dividends were reinvested.

The following table presents information with respect to purchases of common stock we made during the December 2021 quarter. The table reflects shares withheld from employees to satisfy certain tax obligations due in connection with grants of stock under the Delta Air Lines, Inc. Performance Compensation Plan (the "Plan"). The Plan provides for the withholding of shares to satisfy tax obligations but it does not specify a maximum number of shares that can be withheld for this purpose. The shares of common stock withheld to satisfy tax withholding obligations may be deemed to be "issuer purchases" of shares that are required to be disclosed pursuant to this Item.

Our business and operating results continue to be significantly impacted by the COVID-19 pandemic. However, as described further below, we have seen improvement in our business beginning in March 2021 and progressing through 2021. Given the drastic and unprecedented impact of the pandemic on our operating results in 2020, we believe that for the financial highlights discussion below, a comparison of our results in 2021 to both 2020 and 2019 allows for a better understanding of the full impact of the COVID-19 pandemic and the progress of our recovery.

This section of Form 10-K, however, does not address certain items regarding the year ended December 31, 2019. Discussion and analysis of 2019 and year-to-year comparisons between 2020 and 2019 not included in this Form 10-K can be found in "Item 7. Management's Discussion and Analysis" of our Annual Report on Form 10-K for the year ended December 31, 2020. The following discussion and analysis of our financial condition and results of operations should be read in conjunction with our audited Consolidated Financial Statements and the related notes and other financial information as well as the material risk factors included elsewhere in this Annual Report on Form 10-K.

Our pre-tax income for 2021 was $398 million, which includes recognition of $4.5 billion in grants from the Payroll Support Program Extension ("PSP2") and Payroll Support Program 3 ("PSP3"). This is a $5.8 billion decrease compared to 2019 primarily due to the impact of the COVID-19 pandemic on our business which resulted in a 36% decrease in revenue, partially offset by a reduction in operating expense, including the government grant recognition. Pre-tax loss, adjusted (a non-GAAP financial measure) which excludes the government grant recognition and other items was $3.4 billion, a decrease of $9.6 billion compared to 2019.

The length and severity of the reduction in travel demand due to the COVID-19 pandemic remains uncertain; however, with continued distribution of effective vaccines and easing of travel advisories and restrictions, we believe customer confidence will continue to grow, leading to increased demand during 2022. We expect domestic leisure travel to exceed 2019 levels in 2022, while we expect business travel to continue to return as many companies are expected to expand "return to office" plans throughout 2022. International demand recovery has been uneven as the COVID-19 variants and related travel restrictions impact various countries within our international network, though we believe demand will begin accelerating in the second half of 2022 as travel restrictions are lifted. We continue to monitor risks to the pace of recovery from COVID-19 variants, the effectiveness of vaccine programs and travel advisories and restrictions. We are planning for our system capacity to be approximately 15% lower in the March 2022 quarter than the March 2019 quarter and approximately 10% lower for the full year of 2022 compared to 2019.

Our total operating cost per available seat mile ("CASM") decreased 2% to 14.40 cents compared to 2019, primarily due to the cost reductions discussed above and partially offset by a 29% decrease in capacity. Non-fuel unit costs ("CASM-Ex", a non-GAAP financial measure) increased 11% to 12.12 cents due to the 29% decrease in capacity, despite a decline in adjusted operating expenses.

Minimizing unit cost increases is important to delivering on our overall financial objectives. During 2022, however, we expect non-fuel unit costs to increase 7%-10% compared to 2019. This expected unit cost increase is primarily due to 2022 capacity projected to be lower than 2019, costs associated with rebuilding our network, investments to support an elevated customer experience and our premium brand focus, and inflation and labor cost escalation in the underlying business. We expect non-fuel unit cost increases compared to 2019 to moderate in future years as we return to and exceed pre-pandemic capacity and benefit from cost reduction measures implemented during 2020 that were structural in nature.

We have experienced, and expect to continue experiencing, increased cost inflation as a result of global macroeconomic trends, actions we took in response to the COVID-19 pandemic and labor shortages at our suppliers. Actions we have taken to mitigate the impact of expected inflation include leveraging scale and efficiency in our underlying business through improved asset utilization and seeking productivity improvements through increased scale efficiencies and technology enhancements.

The non-GAAP financial measures pre-tax loss, adjusted, operating expense, adjusted, CASM-Ex and free cash flow used above are defined and reconciled in "Supplemental Information" below.

Our 2021 pre-tax income improved $16.0 billion compared to 2020. This was primarily due to the restructuring charges, investment impairments and equity method losses recorded during 2020 and a partial recovery in the demand for air travel during 2021, which resulted in a 75% increase in revenue. Pre-tax loss, adjusted (a non-GAAP financial measure) was $3.4 billion, an increase of $5.6 billion compared to 2020.

Our CASM decreased 35% to 14.40 cents compared to 2020, primarily due to a 45% increase in capacity and reduction in operating expense from the reduction in restructuring charges and recognition of the PSP2 and PSP3 grants as noted above. CASM-Ex (a non-GAAP financial measure) decreased 22% to 12.12 cents.

In the near-term and subject to market dynamics, we also expect to continue the purchase and retirement of verified carbon offsets in support of our $1.0 billion airline carbon neutrality goal. During 2021, we incurred $95 million of expense related to carbon offsets. This amount consists of $30 million to address 13 million metric tons of carbon emissions generated by our airline segment from March 1 to December 31, 2020 through carbon offsets, as well as an additional $65 million for the purchase and retirement of carbon offsets related to a portion of our airline segment's 2021 carbon emissions. The cost of carbon offsets increased significantly during 2021 and will likely continue to do so, which could adversely affect our financial results as we purchase such offsets either in support of our $1.0 billion airline carbon neutrality goal or in satisfaction of future obligations under CORSIA, which are described further in Part I, Item 1, "Business - Environmental Regulation."

Operating Revenue

Our operating revenue increased $12.8 billion, or 75%, compared to the year ended December 31, 2020 due primarily to increased demand in 2021 as a result of the continued recovery from the COVID-19 pandemic. The increase in operating revenue, on a 45% increase in capacity, generated a 21% increase in total revenue per available seat mile ("TRASM") and a 16% increase in TRASM, adjusted (a non-GAAP financial measure) compared to 2020.

See "Refinery Segment" below for additional details on the refinery's operations, including third-party refinery sales recorded in other revenue, during each period.

We have historically generated cargo revenues in domestic and international markets through the use of cargo space on regularly scheduled passenger aircraft. In 2020, following the onset of the COVID-19 pandemic, reduced industry cargo capacity drove a significant increase in our cargo yield, and we also generated cargo revenue through the operation of cargo-only charter flights (i.e., using aircraft in our fleet not being utilized for passenger travel to fly cargo internationally). This trend continued in 2021, and we would expect capacity constraints and elevated market yields to continue through 2022 while the industry rebuilds international networks to pre-pandemic levels. Compared to 2020, we flew additional cargo volume as international networks returned, coupled with a continued increase in yield driven by a combination of constrained capacity and increased demand.

Passenger Revenue by Geographic Region

Domestic passenger unit revenue ("PRASM") for the year ended December 31, 2021 increased 27% with capacity up 45% compared to the year ended December 31, 2020 as a result of the low levels of capacity and demand during 2020 due to the COVID-19 pandemic and the ongoing recovery throughout 2021.

Beginning in the latter half of the March 2021 quarter, we began to see bookings, primarily leisure, improve from the low levels of 2020. Throughout 2021, demand continued to improve, with some variability in periods of rising COVID-19 cases attributable to variants of the virus. We remain optimistic about the ultimate recovery of business travel which has been recovering at a slower pace than consumer. We expect this demand to continue to be led by small- and medium-sized businesses and accelerate in the first half of 2022 as more corporate offices reopen; we are, however, unable to fully predict the pace of that recovery.

International passenger revenue for the year ended December 31, 2021 increased 43% with capacity up 45% compared to the year ended December 31, 2020 as travel to certain destinations has resumed or increased. Additionally, while some countries have removed or eased travel restrictions, many countries maintained or reinstituted international testing requirements and travel restrictions, which have restrained demand in the short term but are expected to support the long-term recovery of international air travel.

In November 2021, travel restrictions on most fully vaccinated foreign visitors to the United States were lifted. This action made travel to the U.S. by many foreign nationals possible for the first time in 18 months. Despite this policy change, we expect the significantly lower international demand environment to continue through at least the beginning of 2022, with the recovery pace continuing to trail domestic travel.

The Atlantic and Pacific regions continue to be the most impacted by the restrictions described above. However, during 2021, we began, resumed or increased our service to certain countries in the Atlantic region based on their lifting or easing of travel restrictions. Travel in the Pacific region is largely limited to essential travel, and we expect only small demand improvements until government restrictions ease with minimal improvement until at least the second half of 2022. We will continue to be agile in the restoration of our international network based on changes in government restrictions and consumer demand.

The Latin America region has shown the most recovery of the international regions, with continued demand improvement for leisure destinations in the Caribbean, Mexico and Central America. We expect this trend to continue through 2022 with the recovery in the Atlantic and Pacific regions lagging behind Latin America.

In order to provide our customers more flexibility and time to plan or rebook their travel, we made the following changes to our ticket and travel credit expiration dates.

In the March 2021 quarter, we announced the extension of the validity of all passenger tickets and travel credits purchased or expiring in 2021 to December 31, 2022, which allowed for tickets to be rebooked through December 31, 2022 for travel through 2023.

In January 2022, we announced that all existing travel credit holders will have until December 31, 2023 to rebook their ticket for travel throughout 2024. Additionally, all Delta customers with upcoming 2022 travel or who purchase a ticket in 2022 will also have the flexibility to rebook their ticket through December 31, 2023, and travel throughout 2024.

During 2020, with the exception of Basic Economy, we eliminated change fees for all tickets originating in North America and waived change fees for tickets originating outside of North America. We also implemented a temporary waiver that allowed Basic Economy tickets with travel for 2021, which are normally non-changeable, to be changed without paying a fee regardless of origin or destination. Starting January 1, 2022, Basic Economy tickets may be cancelled for a fee to receive a partial ticket credit. We do not expect the updated change fee policies to materially affect our revenue in future periods; however, our estimates of revenue that will be recognized for tickets that expire unused ("ticket breakage") may vary in future periods due to the extension of the validity of passenger tickets and travel credits.

In response to the reduced demand and related reduction in revenue following the onset of the COVID-19 pandemic in early 2020, we quickly reduced capacity to more closely align with demand, implemented cost saving initiatives related to our fleet and operations, offered employees voluntary separation programs and delayed or eliminated nearly all discretionary spending.

During 2021, distribution of vaccines continued, travel restrictions and advisories eased and customer confidence continued to grow despite the negative impact of COVID-19 virus variants in the second half of 2021. As a result, we saw revenue and capacity return and related operating expense line items increase. The continued restoration of our operations was the primary driver for the increases in contracted services, landing fees and other rents, passenger commissions and other selling expenses, passenger service and other expense. Other year-over-year fluctuations are discussed below.

Beginning in March 2020 and continuing through December 2020, we reduced salaries by 100% for our CEO and 50% for our officers. In addition, we reduced work hours by 25% for all other management and most front-line employee work groups. On January 1, 2021, employees were restored to full work hours, officer salaries were restored and during 2021 we recalled approximately 1,700 pilots from inactive status back to active service. Additionally, we offered voluntary unpaid leaves of absence for periods ranging from 30 days up to 12 months and approximately 50,000 and 20,000 of our employees elected to take a leave of absence at various times throughout 2020 and 2021, respectively. These actions resulted in higher salaries and related costs in 2021 compared to 2020.

Additionally, during 2021, we purchased and retired $95 million of carbon offsets, of which $30 million relates to 13 million metric tons of carbon emissions generated by our airline segment from March 1 to December 31, 2020 as well as $65 million which relates to a portion of 2021 carbon emissions generated by our airline segment. In the table below, these costs are shown in the carbon offset costs line item.

Until 2021, we allocated certain costs (such as landing fees and other rents, salaries and related costs and contracted services) to regional carrier expense in our Consolidated Statements of Operations ("income statement") based on relevant statistics (such as passenger counts). Beginning in 2021 we ceased performing this allocation and have reclassified the costs presented in prior periods to align with this presentation. This reclassification better reflects the nature of, and how management views, these regional carrier related expenses. This allocation was approximately $900 million in 2020. The amounts in regional carrier expense under the current presentation represent the accrual of payments to our regional carriers under capacity purchase agreements, maintenance costs related to our regional fleet and the expenses of our wholly owned regional subsidiary, Endeavor Air, Inc.

For more information about our income taxes, see Note 11 of the Notes to the Consolidated Financial Statements.

The refinery operated by our wholly-owned subsidiary Monroe primarily produces gasoline, diesel and jet fuel. Monroe has agreements in place to exchange the non-jet fuel products the refinery produces with third parties for jet fuel consumed in our airline operations. Historically, the jet fuel produced and procured through exchanging gasoline and diesel fuel produced by the refinery provided approximately 200,000 barrels per day, or approximately 75% of our pre-COVID-19 pandemic consumption, for use in our airline operations.

The refinery’s production has also been altered by the dramatic change in economic conditions caused by the COVID-19 pandemic. During 2021, the refinery progressively increased operations, ending the year at near pre-pandemic levels.

Refinery revenues increased from $3.1 billion in 2020 to $6.1 billion in 2021, primarily driven by the increase in third-party refinery sales. The increase in third-party refinery sales resulted from the refinery's shift to producing and selling more non-jet fuel products due to the lower level of demand for jet fuel compared to historical levels, in addition to higher pricing during 2021. The refinery decreased its operating loss from $216 million in 2020 to $2 million in 2021 mainly due to the increased production and pricing, partially offset by higher Renewable Identification Numbers ("RINs") compliance costs discussed below.

At December 31, 2021, we had a net fair value obligation of $497 million. Our obligation as of December 31, 2021 was calculated using the EPA's proposed Renewable Fuel Standard ("RFS") volume requirements for 2020 and 2021, which were issued in December 2021. The EPA has not finalized the compliance deadlines to retire our obligations for 2020 and 2021, but we expect those deadlines to be within one year of the effective date of the new RFS volume requirements.

For more information regarding the refinery's results, see Note 14 of the Notes to the Consolidated Financial Statements.

As of December 31, 2021, we had $14.2 billion in cash, cash equivalents, short-term investments and aggregate principal amount committed and available to be drawn under our revolving credit facilities. We expect to meet our liquidity needs for the next twelve months with cash and cash equivalents, short-term investments, restricted cash equivalents and cash flows from operations. We expect to meet our long-term liquidity needs with cash flows from operations and financing arrangements. We are continuing to evaluate the appropriate level of liquidity to maintain following the COVID-19 pandemic though, at least in the near term, we expect this level to be higher than the liquidity maintained prior to the pandemic. By 2024, we expect liquidity to be between $5 billion and $6 billion as we work to reduce our financial obligations and reinvest in the business.

Sources and Uses of Liquidity

Operating Activities

Operating activities in 2021 provided $3.3 billion, including funds received from the government support programs described in "Financing Activities" below, compared to using $3.8 billion in 2020. We expect to continue generating positive cash flows from operations during 2022.

Our operating cash flow is impacted by the following factors:

We expect our commitment to environmental sustainability to depend on increased use of SAF, which is not presently available at scale or at prices competitive to jet fuel. While we do not expect a material adverse effect on our Consolidated Financial Statements in the near-term from the use of SAF, we are unable to predict the financial impact of increased use of SAF on our Consolidated Financial Statements over the longer term as government policies and incentives for, and sufficient third-party investment in, SAF are necessary to make its use in larger quantities commercially and economically feasible.

In addition, we have employee benefit obligations relating primarily to projected future benefit payments from our unfunded postretirement and postemployment plans. See Note 9 of the Notes to the Consolidated Financial Statements for more information on our employee benefit obligations.

To recognize the extraordinary efforts of our employees through the pandemic, we will make a special profit-sharing payment to eligible employees in February 2022, based on the adjusted pre-tax profit earned during the second half of 2021. We will pay $108 million in profit sharing in February 2022.

We continue to plan for further expansion of Terminal 4 and during 2021, the Port Authority approved modified project plans to renovate Terminal 4 and add 10 new gates enabling us to move out of Terminal 2 and consolidate our operations at Terminal 4. The project is estimated to cost approximately $1.5 billion, and we expect to amend the Sublease in the March 2022 quarter. Construction started in late 2021 with the project estimated to be complete by the end of 2023.

We have committed to future aircraft purchases and have obtained, but are under no obligation to use, long-term financing commitments for a substantial portion of the purchase price of the aircraft. Excluding the New York-LaGuardia airport project discussed below, our expected 2022 capital expenditures of approximately $6.0 billion, which may vary depending on financing decisions, will be primarily for aircraft, including deliveries and advance deposit payments, as well as fleet modifications and technology enhancements. As described in Part I, Item 1. "Business - Environmental Sustainability," aircraft fleet renewal is an important component of our environmental sustainability strategy and the path to achievement of our ambitious climate goals, which will continue to require extensive capital investment in future periods. See Note 10 of the Notes to the Consolidated Financial Statements for additional information regarding our aircraft purchase commitments, which totaled approximately $16.2 billion as of December 31, 2021.

In 2019, we opened Concourse G, the first of four new concourses, housing seven of the 37 new gates. Not only did the new Concourse G provide the first direct impact to the Delta passenger experience, it also represented the first major phasing milestone. The next major milestone will be the opening of the headhouse and Concourse E, which is scheduled for the second quarter of 2022.

Given reduced passenger volumes resulting from the COVID-19 pandemic, we accelerated the construction schedule for this project in 2020. Additionally, in 2020, we enhanced the project’s scope to include a more customer-friendly design of Terminal 3, an expanded Delta Sky Club and baggage system upgrades designed to increase the terminals’ operational efficiency going forward. Construction is expected to be completed in 2023.

The project is expected to cost approximately $2.3 billion. A substantial majority of the project costs are being funded through the Regional Airports Improvement Corporation ("RAIC"), a California public benefit corporation, using a revolving credit facility provided by a group of lenders. The credit facility was executed in 2017 and amended in 2020, and we have guaranteed the obligations of the RAIC under the credit facility. The revolving credit facility agreement was amended again in January 2022, increasing the revolver capacity from $800 million to $1.1 billion. Loans made under the credit facility are being repaid with the proceeds from the City’s purchase of completed project assets. Under the lease agreement and subsequent project component approvals by the City's Board of Airport Commissioners, the City has appropriated to date approximately $1.8 billion to purchase completed project assets, representing the maximum allowable reimbursement by the City. Costs incurred in excess of the $1.8 billion maximum will not be reimbursed by the City. We currently expect our net project costs to be approximately $500 million, of which approximately $250 million has been reflected as investing activities in our cash flows statement since the project started in 2017.

In 2021, $487 million was spent on this project, with $450 million paid by the credit facility and $37 million paid directly by Delta. Approximately $500 million is expected to be spent on the project during 2022, with $325 million to be paid by the credit facility and $175 million to be paid directly by Delta.

Financing Activities

The principal amount of our debt and finance leases was $27.1 billion at December 31, 2021.

Our current ratings from the three major credit rating agencies are summarized in the table below:

Our critical accounting estimates are those estimates made in accordance with GAAP that involve a significant level of estimation uncertainty and have had or are reasonably likely to have a material impact on our consolidated results of operations or financial condition. Accordingly, the actual results may differ materially from these estimates. For a discussion of our significant accounting policies, see Note 1 of the Notes to the Consolidated Financial Statements, unless otherwise noted below.

Loyalty Program

Our SkyMiles loyalty program generates customer loyalty by rewarding customers with incentives to travel on Delta. This program allows customers to earn mileage credits ("miles") by flying on Delta, Delta Connection carriers and other airlines that participate in the loyalty program. When traveling, customers earn miles primarily based on the passenger's loyalty program status, fare class and ticket price. Customers can also earn miles through participating companies such as credit card companies, hotels, car rental agencies and ridesharing companies. Miles are redeemable by customers in future periods for air travel on Delta and other participating airlines, access to our Sky Club and other program awards. To facilitate transactions with participating companies, we sell miles to non-airline businesses, customers and other airlines.

The loyalty program includes two types of transactions that are considered revenue arrangements with multiple performance obligations (1) passenger ticket sales earning miles and (2) sale of miles to participating companies.

At December 31, 2021, the aggregate deferred revenue balance associated with the SkyMiles program was $7.6 billion. A hypothetical 10% change in the number of outstanding miles estimated to be redeemed would result in an impact of approximately $140 million on total operating revenue recognized for the year ended December 31, 2021.

We defer revenue for the miles when earned and recognize loyalty travel awards in passenger revenue as the miles are redeemed and transportation is provided. We record the air transportation portion of the passenger ticket sales in air traffic liability and recognize passenger revenue when we provide transportation or if the ticket goes unused. A hypothetical 10% increase in our estimate of the ETV of a mile would have decreased total operating revenue by approximately $60 million for the year ended December 31, 2021, as a result of an increase in the amount of revenue deferred associated with the miles earned.

Our most significant contract to sell miles relates to our co-brand credit card relationship with American Express. Our agreements with American Express provide for joint marketing, grant certain benefits to Delta-American Express co-branded credit card holders ("cardholders") and American Express Membership Rewards program participants, and allow American Express to market its services or products using our customer database. Cardholders earn miles for making purchases using co-branded cards, and certain cardholders may also check their first bag for free, are granted discounted access to Delta Sky Club lounges and receive priority boarding and other benefits while traveling on Delta. Additionally, participants in the American Express Membership Rewards program may exchange their points for miles under the loyalty program. We sell miles at agreed-upon rates to American Express which are then provided to their customers under the co-brand credit card program and the Membership Rewards program.

We account for marketing agreements, including those with American Express, by allocating the consideration to the individual products and services delivered. We allocate the value based on the relative selling prices of those products and services, which generally consist of award travel, priority boarding, baggage fee waivers, lounge access and the use of our brand. We determine our best estimate of the selling prices by using a discounted cash flow analysis using multiple inputs and assumptions, including (1) the expected number of miles awarded and number of miles redeemed, (2) ETV for the award travel obligation adjusted for mileage breakage, (3) published rates on our website for baggage fees, discounted access to Delta Sky Club lounges and other benefits while traveling on Delta, (4) brand value (using estimated royalties generated from the use of our brand) and (5) volume discounts provided to certain partners.

We defer the amount allocated to award travel as part of loyalty program deferred revenue and recognize loyalty travel awards in passenger revenue as the miles are redeemed and transportation is provided. Revenue allocated to services performed in conjunction with a passenger’s flight, such as baggage fee waivers, is recognized as travel-related services in passenger revenue when the related service is performed. Revenue allocated to access Delta Sky Club lounges is recognized as miscellaneous in other revenue as access is provided. Revenue allocated to the remaining performance obligations, primarily brand value, is recorded as loyalty program in other revenue as miles are delivered.

The timing of mile redemptions can vary widely; however, the majority of new miles have historically been redeemed within two years of being earned. The loyalty program deferred revenue classified as a current liability represents our current estimate of revenue expected to be recognized in the next twelve months based on projected redemptions, while the balance classified as a noncurrent liability represents our current estimate of revenue expected to be recognized beyond twelve months. Compared to pre-pandemic levels, a larger portion of mile redemptions is projected to occur beyond twelve months and is therefore reflected as a noncurrent liability as of December 31, 2021. We will continue to monitor redemptions as the situation evolves.

For additional information on our significant accounting policies related to the loyalty program, see Note 2 of the Notes to the Consolidated Financial Statements.

Passenger Ticket Sales

We defer sales of passenger tickets to be flown by us or that we sell on behalf of other airlines in our air traffic liability. Passenger revenue is recognized when we provide transportation or when the ticket expires unused ("ticket breakage"). For tickets that we sell on behalf of other airlines, we reduce the air traffic liability when consideration is remitted to those airlines. The air traffic liability primarily includes sales of passenger tickets with scheduled departure dates in the future and credits which can be applied as payment toward the cost of a ticket ("travel credits"). Travel credits are typically issued as a result of ticket cancellations prior to their expiration dates. We periodically evaluate the estimated air traffic liability and may record adjustments in our income statement. These adjustments relate primarily to refunds, exchanges, ticket breakage, transactions with other airlines and other items for which final settlement occurs in periods subsequent to the sale of the related tickets at amounts other than the original sales price.

We have experienced significant ticket cancellations, particularly in the early months of the pandemic in 2020. During 2020, with the exception of Basic Economy, we eliminated change fees for all tickets originating in North America and waived change fees for tickets originating outside of North America. In the March 2021 quarter, we announced the extension of the validity of all passenger tickets and travel credits purchased or expiring in 2021 to December 31, 2022, which allowed for tickets to be rebooked through December 31, 2022 for travel through 2023. In January 2022, we announced that all existing travel credit holders will have until December 31, 2023 to rebook their ticket for travel throughout 2024. Additionally, all Delta customers with upcoming 2022 travel or who purchase a ticket in 2022 will also have the flexibility to rebook their ticket through December 31, 2023, and travel throughout 2024.

We estimate the value of ticket breakage and recognize revenue at the scheduled flight date. Our ticket breakage estimates are primarily based on historical experience, ticket contract terms and customers’ travel behavior. Given the impact of the COVID-19 pandemic on customer behavior and changes made in ticket validity terms, as well as the elimination of change fees for most tickets, our estimates of revenue that will be recognized from the air traffic liability for unused tickets may vary in future periods. Travel credits represented approximately 45% of the air traffic liability as of December 31, 2021. This compares to approximately 65% as of December 31, 2020 and approximately 20% prior to the onset of the COVID-19 pandemic.

For additional information on our significant accounting policies related to passenger ticket sales, see Note 2 of the Notes to the Consolidated Financial Statements.

Long-Lived Assets

Our long-lived lived assets, including flight equipment, which consists of aircraft and associated engines and parts, operating lease right-of-use ("ROU") assets and other long-lived assets, which have a recorded value of approximately $36.0 billion at December 31, 2021, are recorded in property and equipment, net and operating lease right-of-use assets on our balance sheets. This value is based on various factors, including the assets' acquisition costs, estimated useful lives, salvage values, discounted lease payments and lease terms. We review flight equipment, ROU assets and other long-lived assets used in operations for impairment losses when events and circumstances indicate the assets may be impaired. Factors which could be indicators of impairment include, but are not limited to (1) a decision to permanently remove flight equipment or other long-lived assets from operations, (2) significant changes in the estimated useful life, (3) significant changes in projected cash flows, (4) permanent and significant declines in fleet fair values and (5) changes to the regulatory environment. For long-lived assets held for sale, we discontinue depreciation and record impairment losses when the carrying amount of these assets is greater than the fair value less the cost to sell.

To determine whether impairments exist for aircraft used in operations, we group assets at the fleet type level or at the contract level for aircraft operated by third-party regional carriers (i.e., the lowest level for which there are identifiable cash flows) and then estimate future cash flows based on projections of capacity, passenger mile yield, fuel and labor costs and other relevant factors. If an asset group is impaired, the impairment loss recognized is the amount by which the asset group's carrying amount exceeds its estimated fair value. We estimate aircraft fair values using published sources, appraisals and bids received from third parties, as available.

As a result of the COVID-19 pandemic and our response, we made decisions to remove certain aircraft from active service and to early retire certain fleets. We evaluated our fleet during 2020 and determined that only the fleet types discussed in Note 15 of the Notes to the Consolidated Financial Statements were impaired, as the future cash flows from the operation of other fleet types through the respective retirement dates exceeded the carrying value. This resulted in impairment and other related charges of $4.4 billion, recorded in restructuring charges in our income statement. These charges were calculated using Level 3 fair value inputs based primarily upon recent market transactions and third-party bids, which were corroborated with published pricing guides and our assessment of existing market conditions based on industry knowledge. The effects of the COVID-19 pandemic created additional estimation uncertainty as there was a limited market for aircraft and limited data on how the COVID-19 pandemic affected the fair value of aircraft.

Due to the recovery in demand that we have experienced throughout 2021, we decided not to retire any additional aircraft and returned to service a majority of the aircraft that were temporarily parked in 2020. We recorded no further impairments during 2021. As we gained updated information during the year, we updated estimates to the 2020 fleet-related impairment charges and recorded adjustments of $19 million to certain of the restructuring charges during 2021.

Following the impairment charges, the aggregate net book value of these aircraft as of December 31, 2021 and December 31, 2020 was approximately $340 million and $500 million, respectively, with the reduction in 2021 primarily due to aircraft sales. See Note 15 of the Notes to the Consolidated Financial Statements for additional details regarding these impairments and related charges.

Goodwill and Indefinite-Lived Intangible Assets

We apply a fair value-based impairment test to the carrying value of goodwill and indefinite-lived intangible assets on an annual basis (as of October 1) and, if certain events or circumstances indicate that an impairment loss may have been incurred, on an interim basis. We assess the value of our goodwill and indefinite-lived assets under either a qualitative or quantitative approach. Under a qualitative approach, we consider various market factors, including certain of the key assumptions listed below. We analyze these factors to determine if events and circumstances have affected the fair value of goodwill and indefinite-lived intangible assets. If we determine that it is more likely than not that the asset may be impaired, we use the quantitative approach to assess the asset's fair value and the amount of the impairment. Under a quantitative approach, we calculate the fair value of the asset incorporating the key assumptions listed below into our calculation.

When we evaluate goodwill for impairment using a quantitative approach, we estimate the fair value of the reporting unit by considering both comparable public company multiples (a market approach) and projected discounted future cash flows (an income approach). When we perform a quantitative impairment assessment of our indefinite-lived intangible assets, fair value is estimated based on (1) recent market transactions, where available, (2) the royalty method for the Delta tradename (which assumes hypothetical royalties generated from using our tradename) or (3) projected discounted future cash flows (an income approach).

Changes in certain events and circumstances could result in impairment or a change from indefinite-lived to definite-lived. Factors which could cause impairment include, but are not limited to (1) negative trends in our market capitalization, (2) reduced profitability resulting from lower passenger mile yields or higher input costs (primarily related to fuel and employees), (3) lower passenger demand as a result of weakened U.S. and global economies, global pandemics or other factors, (4) interruption to our operations due to a prolonged employee strike, terrorist attack or other reasons, (5) changes to the regulatory environment (e.g., changes in slot access and/or availability, additional Open Skies agreements or changes to antitrust approvals), (6) competitive changes by other airlines and (7) strategic changes to our operations leading to diminished utilization of the intangible assets.

In 2021, we performed qualitative assessments of our goodwill and indefinite-lived intangible assets, including applicable factors noted in "Key Assumptions" above, and determined that there was no indication that the assets were impaired. Our qualitative assessments include analyses and weighting of all relevant factors, which impact the fair value of our indefinite-lived intangible assets.

For additional information on our goodwill and indefinite-lived intangible assets' significant accounting policies and the related fair values and book values, see Note 5 of the Notes to the Consolidated Financial Statements.

Defined Benefit Pension Plans

We sponsor defined benefit pension plans for eligible employees and retirees. These plans are closed to new entrants and frozen for future benefit accruals. As of December 31, 2021, the unfunded benefit obligation for these plans recorded on our Consolidated Balance Sheets ("balance sheets") was $1.6 billion. We had no minimum funding requirements in 2020 or 2021, and have no such requirements in 2022. However, we voluntarily contributed $1.5 billion to these plans during 2021. The most critical assumptions impacting our defined benefit pension plan obligations and net periodic benefit cost are the discount rate, the expected long-term rate of return on plan assets and life expectancy of plan participants.

The investment strategy for our defined benefit pension plan assets is to earn a long-term return that meets or exceeds our annualized return target while taking an acceptable level of risk and maintaining sufficient liquidity to pay current benefits and other cash obligations of the plan. Based on our current level of funding, we have modified, and continue to evaluate, the asset allocation mix to reduce the investment risk of the portfolio. The lower risk profile of the portfolio is projected to result in a lower expected long-term rate of return on plan assets in 2022.

The impact of a 0.50% change in weighted average discount rate and 1.00% change in expected long-term rate of return on assets are shown in the table below:

While this recent legislation makes our funding obligations for these plans more predictable, factors outside our control continue to have an impact on the funding requirements. Estimates of future funding requirements are based on various assumptions and can vary materially from actual funding requirements. Assumptions include, among other things, the actual and projected market performance of assets, statutory requirements and demographic data for participants.

For additional information on our significant accounting policies related to defined benefit pension plans, see Note 9 of the Notes to the Consolidated Financial Statements.

Income Tax Valuation Allowance

Our federal net operating loss carryforwards generated before 2018 do not begin to expire until 2029. Under current tax law, federal net operating losses generated after 2017 do not expire. Therefore, we have not recorded a valuation allowance on our deferred tax assets other than the capital loss carryforwards and certain state net operating losses that have short expiration periods.

For additional information on our significant accounting policies related to income taxes, see Note 11 of the Notes to the Consolidated Financial Statements.

Recent Accounting Standards

We sometimes use information ("non-GAAP financial measures") that is derived from the Consolidated Financial Statements, but that is not presented in accordance with GAAP. Under the U.S. Securities and Exchange Commission rules, non-GAAP financial measures may be considered in addition to results prepared in accordance with GAAP, but should not be considered a substitute for or superior to GAAP results. Reconciliations below may not calculate exactly due to rounding.

Included below are reconciliations of non-GAAP measures used within this Form 10-K to the most directly comparable GAAP financial measures. These reconciliations include certain adjustments to GAAP measures, which are directly related to the impact of COVID-19 and our response. These adjustments are made to provide comparability between the reported periods, if applicable, as indicated below:

We also regularly adjust certain GAAP measures for the following items, if applicable, for the reasons indicated below:

Free Cash Flow

The following table shows a reconciliation of net cash provided by/(used in) operating activities (a GAAP measure) to free cash flow (a non-GAAP financial measure). We present free cash flow because management believes this metric is helpful to investors to evaluate the company's ability to generate cash that is available for use for debt service or general corporate initiatives. Adjustments include: