We rely on maintaining a high daily aircraft utilization rate to implement our low-cost structure, which makes us especially vulnerable to flight delays, flight cancellations, aircraft unavailability or unplanned reductions in demand such as has been caused by the COVID-19 pandemic.
We have maintained a high daily aircraft utilization rate prior to the COVID pandemic and expect our utilization rate to increase as the U.S. market begins to recover from the pandemic. Our average daily aircraft utilization was 12.3 hours, 12.2 hours and 8.0 hours for the years ended December 31, 2018, 2019, and 2020, respectively. Aircraft utilization is the average amount of time per day that our aircraft spend carrying passengers. Part of our business strategy is to maximize revenue per aircraft through high daily aircraft utilization, which is achieved, in part, by quick turnaround times at airports so we can fly more hours on average in a day. Aircraft utilization is reduced by delays and cancellations caused by various factors, many of which are beyond our control, including air traffic congestion at airports or other air traffic control problems or outages, labor availability, adverse weather conditions, increased security measures or breaches in security, international or domestic conflicts, terrorist activity, or other changes in business conditions. A significant portion of our operations are concentrated in markets such as Denver, the Northeast and northern Midwest regions of the United States, which are particularly vulnerable to weather, airport traffic constraints and other delays, particularly in the winter months. In addition, pulling aircraft out of service for unscheduled and scheduled maintenance may materially reduce our average fleet utilization and require that we re-accommodate passengers or seek short-term substitute capacity at increased costs. Further, an unplanned reduction in demand such as has been caused by the COVID-19 pandemic reduces the utilization of our fleet and result in a related increase in unit costs, which may be material. Due to the relatively small size of our fleet, our point-to-point network and high daily aircraft utilization rate, the unexpected unavailability of one or more aircraft and resulting reduced capacity or even a modest decrease in demand could have a material adverse effect on our business, results of operations and financial condition.
It has only been a limited period since our current business and operating strategy has been implemented.
Following our acquisition by an investment fund managed by Indigo, an affiliate of Indigo Partners, in 2013 and the implementation of our current business and operating strategy in 2014, we recorded net income of $80 million and $251 million for the years ended December 31, 2018 and 2019, and net loss of $225 million for the year ended December 31, 2020, respectively, which, with respect to 2018 and 2019, are higher levels of net income than we had achieved prior to our acquisition. While we recorded an annual profit for the years ended December 31, 2018 and 2019, we recorded a net loss for the year ended December 31, 2020 and we cannot assure you that we will be able to sustain or increase profitability on a quarterly or an annual basis in future periods. In turn, this may cause the trading price of our common stock to decline and may materially adversely affect our business.
We are subject to various environmental and noise laws and regulations, which could have a material adverse effect on our business, results of operations and financial condition.
We are subject to increasingly stringent federal, state, local and foreign laws, regulations and ordinances relating to the protection of the environment and noise, including those relating to emissions to the air, discharges (including storm water discharges) to surface and subsurface waters, safe drinking water and the use, management, disposal and release of, and exposure to, hazardous substances, oils and waste materials. We are or may be subject to new or proposed laws and regulations that may have a direct effect (or indirect effect through our third-party specialists or airport facilities at which we operate) on our operations. In addition, U.S. airport authorities are exploring ways to limit de-icing fluid discharges. Any such existing, future, new or potential laws and regulations could have an adverse impact on our business, results of operations and financial condition.
Similarly, we are subject to environmental laws and regulations that require us to investigate and remediate soil or groundwater to meet certain remediation standards. Under certain laws, generators of waste materials, and current and former owners or operators of facilities, can be subject to liability for investigation and remediation
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