Early in the pandemic, there was a glut of empty flights as airlines were surprised by how quickly people decided to cancel trips and forgo new bookings. Flight schedules are set weeks in advance and airlines didn’t know how many passengers would actually board planes.

Over time, however, airlines have slashed their schedules. United, for example, cut flights in May by about 90 percent. Delta Air Lines has cut 85 percent of its flights over the three months ending in June.

“That means that people who are on four individual flights are now on one — the single flight that remains,” said Robert Mann, an industry analyst and consultant.