Airport-related expenses. Airport-related expenses include airport-related customer service costs such as outsourced airport gate and ramp agent services, airport security fees, passenger interruption costs, deicing, landing fees and station rents (our employee customer service labor costs are reflected in salaries, wages and benefits). The decrease in airport-related expenses was primarily due to a decrease in deicing events partially offset by an increase in airport terminal rents and subcontract airport services related to our prorate operations during the three months ended March 31, 2020.
Aircraft rentals. The $3.1 million decrease in aircraft rentals was primarily related to a reduction of our fleet size that was financed through leases as a result of scheduled lease expirations subsequent to March 31, 2019.
Special Items. The $21.9 million special items expense for the three months ended March 31, 2019 related to a non-cash write-off of $18.5 million in aircraft manufacturer part credits that we forfeited to settle future lease return obligations with the aircraft manufacturer. The $18.5 million of expense was included in the SkyWest Airlines segment. The special items expense also included $3.4 million of expense associated with a cash payout of certain ExpressJet employees stock equity grants as part of the sale of ExpressJet, which was reflected in the ExpressJet segment. We did not have a comparable special items expense during the three months ended March 31, 2020.
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 $6.3 million increase in other operating expenses was primarily related to credit loss reserves recorded, resulting from our adoption of Accounting Standards Update 2016-13, “Financial Instruments – Credit Losses (Topic 326), Measurement of Credit Losses on Financial Instruments” (“Topic 326”) during the three months ended March 31, 2020.
Interest Expense. The $2.3 million increase in interest expense was primarily related to the additional interest expense associated with the nine new E175 aircraft added to our fleet subsequent to March 31, 2019, which were debt financed.
Total airline expenses. The $34.0 million increase in total airline expenses was primarily related to additional operating expenses at SkyWest Airlines and SkyWest Leasing that resulted from new, additional aircraft we placed into service since March 31, 2019, partially offset by the sale of ExpressJet and the related expenses associated with ExpressJet’s prior operations during the three months ended March 31, 2019.
Summary of interest income, other income (expense) and provision for income taxes:
Interest income. Interest income decreased $1.2 million, or 32.7%, during the three months ended March 31, 2020, compared to the three months ended March 31, 2019. The decrease in interest income was primarily related to a decrease in interest rates subsequent to March 31, 2019.
Other income (expense), net. During the three months ended March 31, 2020, we had other income, net of $0.4 million primarily related to income earned from our investment in a joint venture with a third party. During the three months ended March 31, 2019, we had other income of $46.7 million primarily related to the gain on sale of ExpressJet.
Income taxes. Our provision for income taxes was 23.3% and 23.0% for the three months ended March 31, 2020 and 2019, respectively. The increase in the effective tax rate primarily relates to a lower discrete tax benefit from excess tax deductions generated from employee equity transactions that occurred during the three months ended March 31, 2020 compared to the three months ended March 31, 2019.
Net income. Primarily due to the factors described above, we generated net income of $30.0 million, or $0.59 per diluted share, for the three months ended March 31, 2020, compared to net income of $88.2 million, or $1.69 per diluted share, for the three months ended March 31, 2019.