Thousands of travelers were left stranded on Monday after two of the country's largest airlines canceled almost 1,000 flights.
American Airlines canceled or delayed 1,500 flights on Monday - more than half of their scheduled itinerary - with its Dallas/Fort Worth hub bearing the brunt.
The airline canceled 562 flights on Monday, representing 18 per cent of all their departures, and saw a further 32 per cent - 979 flights - delayed, according to FlightAware.com.
Spirit canceled 400 on Sunday and Monday, with Spirit's toll accounting for 30 percent of its scheduled flights nationwide. Orlando and Fort Lauderdale were hard hit, with 40 per cent of Orlando's flights canceled or delayed on Monday, and 37 per cent of Fort Lauderdale's.
Despite rising numbers of coronavirus infections fueled by the delta variant, the U.S. set another recent high mark for air travel Sunday, with more than 2.2 million people going through airport checkpoints, according to the Transportation Security Administration.
That is nearly 11,000 more people screened than July 18, and the highest number since Feb. 28, 2020, before the U.S. felt the full brunt of the pandemic.
However, air travel was still down 17 per cent on Sunday from the same Sunday in 2019.
The resurgence of leisure travel, coupled with some bad weather, has led to delays and flight cancellations at airlines struggling to ramp up after being crushed by the pandemic.
Airlines have thousands fewer workers than they did before the pandemic, and at times they have been caught short-staffed even though they received $54 billion in taxpayer money to keep employees on the payroll.
San Juan international airport in Puerto Rico was hard-hit by Spirit's cancelations, with many people now stuck on the island for days
One Instagram user posted a photo on Sunday of a sign jokingly reading: 'Pilot wanted'
Passengers were left lying on airport floors for hours as Spirit and American Airlines canceled hundreds of flights
Monday's cancellations came one day after 7,400 U.S. flights arrived at least 15 minutes behind schedule on Sunday — the government's definition of late — and more than 900 were canceled, according to tracking service FlightAware.
Nearly half of Sunday's cancellations were at Dallas/Fort Worth International Airport, American's largest hub, which was hit with afternoon and evening thunderstorms.
There have been at least 5,000 delayed flights on most days since early July, according to FlightAware figures.
Southwest, American and Spirit are among airlines with the biggest problems.
For Sunday and Monday combined, Southwest delayed more than 2,500 flights and American more than 1,600.
A key senator is quizzing several airlines to explain the high numbers of flight delays and cancellations.
Senator Maria Cantwell, chair of the Senate Commerce Committee, said airlines did a poor job of managing their workforces and might have failed to live up to the purpose of the taxpayer funding.
'I am deeply concerned by recent reports highlighting…workforce shortages that have caused flight cancellations and generated delays for passengers,' she wrote in a July 16 letter to the CEOs of American Airlines, Delta Air Lines, JetBlue Airways, Southwest Airlines, Republic Airways, and Allegiant Airlines.
'These shortages come in the wake of unprecedented federal funding that Congress appropriated, at the airlines' request, to support the airline industry during the COVID-19 pandemic.
'As passenger travel has boomed in recent weeks, new reports also suggest that some airlines are now unprepared to meet the increased demand that they scheduled for, and have resorted to delaying or canceling flights,' the Senator continued.
'This reported workforce shortage runs counter to the objective and spirit of the PSP, which was to enable airlines to endure the pandemic and keep employees on payroll so that the industry was positioned to capture a rebound in demand.'
Cantwell asked each airline to account for its utilization of federal funds and provide further information on current and projected workforce shortages.
Ed Bastian, CEO of Delta, said earlier in July that 'the challenges of getting our airline fully back to the service level our customers expect and deserve is
