Making money in the summer is not as easy as it used to be for airlines.

Airlines have drawn down their schedules in August for a variety of reasons. Some travelers are opting to fly earlier, in June or even May, as schools let out sooner than they used to. Demand for flights to Europe has also been moving from the sweltering, crowded summer to the fall, airline executives have said, especially for travelers with more flexibility, like retirees.

Carriers still make the bulk of their money in the second and third quarters. But as travel demand has shifted, and in some cases customers have become altogether unpredictable, making the third quarter less of a shoo-in moneymaker for airlines.

Airline planners have been forced to get more surgical with schedules in August as leisure demand tapers off from the late spring and summer peaks. Labor and other costs have jumped after the pandemic, so getting the mix of flights right is essential.

Carriers across the industry have been taking flights off the schedule after an overhang of too much capacity pushed down fares this summer. But the capacity cuts are set to further drive up airfares, which rose 0.7% in July from last year, and a seasonally adjusted 4% jump from June to July, according to the latest U.S. inflation read.