Aircraft rentals. The $19.5 million decrease in aircraft rentals was primarily due to the acquisition of 52 CRJ aircraft under an early lease buyout arrangement during the three months ended March 31, 2019 and through a reduction of our fleet size that was financed through leases because of scheduled lease expirations subsequent to June 30, 2018.
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 $7.3 million decrease in other operating expenses was primarily related to the sale of ExpressJet and the related decrease in crew costs associated with the decrease in expenses associated with that operation.
Interest Expense. The $4.0 million increase in interest expense was primarily related to the additional interest expense associated with the 25 E175 aircraft added to our fleet subsequent to June 30, 2018, which were debt financed.
Total airline expenses. The $74.6 million decrease in total airline expenses was primarily related to the sale of ExpressJet and the related expenses associated with ExpressJet’s prior operations, partially offset by additional operating expenses at SkyWest Airlines and SkyWest Leasing that resulted from new, additional aircraft we placed into service since June 30, 2018.
Summary of interest income, other income (expense) and provision for income taxes:
Interest income. Interest income increased $2.0 million, or 118.8%, during the three months ended June 30, 2019, compared to the three months ended June 30, 2018. The increase in interest income was primarily related to an increase in interest rates subsequent to June 30, 2018, and an increase in interest earned from loans to third parties.
Other income (expense). During the three months ended June 30, 2019, we had other income of $0.3 million primarily related to investments in joint ventures with third parties. During the three months ended June 30, 2018, we had other expenses of $1.2 million primarily related to a mark-to-market loss on trading securities sold.
Income taxes. Our provision for income taxes was 23.7% and 22.9% for the three months ended June 30, 2019 and 2018, respectively. The increase in the effective tax rate primarily relates to a tax benefit that was recorded in for the three months ended June 30, 2018 related to the release of a valuation allowance for capital loss carryforwards.
Net income. Primarily due to the factors described above, we generated net income of $88.1 million, or $1.71 per diluted share, for the three months ended June 30, 2019, compared to net income of $75.9 million, or $1.43 per diluted share, for the three months ended June 30, 2018.
Six Months Ended June 30, 2019 and 2018
Operational Statistics. The following table sets forth our major operational statistics and the associated percentage changes for the six months ended June 30, 2019 and 2018:
| | | | | | | |
| | For the six months ended June 30, | |
| | 2019 | | 2018 | | % Change | |
SkyWest Airlines block hours | | 720,171 | | 673,228 | | 7.0 | % |
ExpressJet block hours | | 16,904 | | 202,313 | | (91.6) | % |
Total block hours | | 737,075 | | 875,541 | | (15.8) | % |
| | | | | | | |
SkyWest Airlines Only | | | | | | | |
Departures | | 408,527 | | 385,065 | | 6.1 | % |
Passengers carried | | 20,998,133 | | 19,317,005 | | 8.7 | % |
Passenger load factor | | 81.4 | % | 80.8 | % | 0.6 | pts |
Average passenger trip length (miles) | | 501 | | 490 | | 2.2 | % |
During the six months ended June 30, 2018, ExpressJet had 118,623 departures and 4,342,856 passengers carried. The number of ExpressJet departures and passengers carried was not significant for the six months ended June