At least 800 more flights were canceled on Monday after a chaotic travel weekend

Participate (VALLEY) alone canceled at least 224 flights on Monday, or 7% of operations, while united (UAL) canceled 128 flights and American Airlines (EEL) nixed 67. CNN has contacted the three airlines to comment on the flight cancellations.

“Delta teams continue to steer safely through complex factors affecting our operations this weekend, including higher than planned unplanned absences in some of our workgroups, weather and air traffic control constraints,” a Delta Air Lines spokesman said Sunday. “Canceling a flight is always our last resort, and we strongly apologize to our customers for any disruption to their travel plans.”

It’s going to be a summer of travel hell, experts warn. Although airlines received $ 54 billion in federal assistance under Covid’s summit to avoid involuntary redundancies, they now have fewer employees than before the pandemic – especially pilots – after offering acquisitions and early retirement packages to trim employees and save money. As a result, operations can quickly fall apart in bad weather, understaffed air traffic control centers or sick employees.

Atlanta’s Hartsfield-Jackson International Airport and the Newark City area’s Newark Liberty International were most affected by Monday’s cancellations, with Newark alone accounting for more than 100 canceled flights.

United – which canceled 56 flights on Saturday and 70 flights on Sunday – had said last Thursday that it would cut 12% of its daily domestic flights from the busy Newark hub. The cuts start in July and amount to about 50 daily flights.

According to FlightAware, there were 634 US flight cancellations on Saturday and 868 canceled on Sundays.

“More than ever in our history, the various factors that currently affect our operations – weather and air traffic control, supplier staffing, increased Covid case numbers that contribute to higher than planned unplanned absences in some workgroups – result in an operation that is inconsistent up to the standards Delta has set for the industry in recent years, “said Delta Chief Customer Experience Officer Allison Ausband in an online post.

But critics say airlines should have anticipated these problems before the summer travel season.

“When you stress test the airline’s operating model, that’s when you see the same results,” said Captain Dennis Tajer, spokesman for the Allied Pilots Association, the pilot association at American Airlines, earlier this month.

With flights already booked to capacity, “a flight that is canceled not only causes a cascade effect, it causes a tidal wave of problems. It’s déjà vu again,” Tajer added, referring to the chaotic holiday season late last year.

CNN Business’ Chris Isidore contributed to this report.