and station rents. The $0.9 million, or 5.1%, increase in airport-related expenses for the three months ended September 30, 2023, compared to the three months ended September 30, 2022, was primarily due to an increase in station rents and associated costs.
Aircraft rentals. The $14.0 million, or 87.0%, decrease in aircraft rentals was primarily related to a decrease in our leased aircraft since the three months ended September 30, 2022 as a result of our acquisition of 26 CRJ700 aircraft, eight CRJ200 aircraft and one CRJ900 aircraft under early lease buyouts during 2023.
Other operating expenses. Other operating expenses primarily consist of property taxes, hull and liability insurance, simulator costs, crew per diem and crew hotel costs. The $1.3 million, or 2.0%, increase was primarily related to an increase in crew hotel rates and training costs during the three months ended September 30, 2023, compared to the three months ended September 30, 2022.
Summary of interest expense, interest income, other income (loss), net and provision for income taxes
Interest Expense. The $0.7 million, or 2.2%, decrease in interest expense was primarily related to a decrease in outstanding debt from $3.4 billion at September 30, 2022 to $3.1 billion at September 30, 2023, partially offset by higher fixed interest rates on debt issued since September 30, 2022.
Interest income. Interest income increased $4.9 million, from $6.3 million for the three months ended September 30, 2022, to $11.2 million for the three months ended September 30, 2023. The increase in interest income was primarily related to an increase in average interest rates attributed to our marketable securities for the three months ended September 30, 2023, compared to the three months ended September 30, 2022.
Other income (loss), net. Other income (loss), net decreased $11.7 million during the three months ended September 30, 2023, compared to the three months ended September 30, 2022. Other income (loss), net primarily consists of the realized and unrealized gains on our investments in other companies, income related to our investment in a joint venture with a third party and gains or losses on the sale of assets. The decrease in other income (loss), net was primarily a result of a decrease in unrealized gains on our investments in other companies, partially offset by gains from the sale of assets for the three months ended September 30, 2023, compared to the three months ended September 30, 2022.
Provision for income taxes. For the three months ended September 30, 2023 and 2022, our effective income tax rates were 3.6% and 14.8%, respectively, which included the statutory federal income tax rate of 21% and other reconciling income tax items, including state income taxes and the impact of non-deductible expenses. The decrease in the effective tax rate primarily related to lower pre-tax income for the three months ended September 30, 2023, compared to the three months ended September 30, 2022 and a partial release of the valuation allowance on state net operating losses anticipated to be utilized prior to expiration for the three months ended September 30, 2023, compared the three months ended September 30, 2022.
Net income. Primarily due to the factors described above, we generated net income of $23.5 million, or $0.55 per diluted share, for the three months ended September 30, 2023, compared to net income of $48.4 million, or $0.96 per diluted share, for the three months ended September 30, 2022.
Nine Months Ended September 30, 2023 and 2022
Operational Statistics
The following table sets forth our major operational statistics and the associated percentage changes for the periods identified below. The decrease in block hours, departures and passengers carried during the nine months ended September 30, 2023, compared to the nine months ended September 30, 2022, was primarily due to labor constraints, including a smaller number of available captains during the nine months ended September 30, 2023, compared to the nine months ended September 30, 2022.