The travel chaos continues for an eighth consecutive day Friday, with more than 1,600 U.S. cancellations as of 8:30 p.m. ET. The airlines have been grappling with the one-two punch of bad winter weather and a surge in crew COVID cases that have left them short-staffed, and forced airlines to cancel nearly 10,000 flights since Christmas Eve.
Now the Federal Aviation Administration is warning of staffing issues of its own, such as sick air traffic controllers. In addition, the FAA warned on Thursday that weather, holiday traffic and COVID-19 "are likely to result in some travel delays in the coming days."
"Like the rest of the U.S. population, an increased number of FAA employees have tested positive for COVID-19," the FAA said in a statement. "To maintain safety, traffic volume at some facilities could be reduced, which might result in delays during busy periods."
The travel turbulence couldn't have come at a worse time as millions of Americans travel during what could be the busiest travel period since the start of the pandemic. Roughly 8.5 million fliers are expected to pass through U.S. airports from now until Jan.3, according to estimates from the Transportation Security Administration.
Seattle-Tacoma International Airport has been hit particularly hard this week -- holding the No. 1 spot for the most cancellations in the world for three days in a row. Denver International took its place on Friday morning, topping the list with more than 250 cancellations.
Carriers are trying to proactively cancel flights to give travelers time to rebook.
JetBlue Airways, which has seen sick calls in some departments up 200-300% more than average, canceled more than 1,200 flights over the next few weeks.
"We expect the number of COVID cases in the northeast -- where most of our crewmembers are based -- to continue to surge for the next week or two," the airline said in a statement. "This means there is a high likelihood of additional cancellations until case counts start to come down."
Delta Air Lines is already planning to cancel 200 to 300 daily flights for the upcoming weekend, citing "increasing winter weather and the omicron variant."
Thousands of travelers who have had to call the airlines to change their flights have been met with long wait times.
Alaska Airlines was reporting hold times of up to 20 hours on Thursday.
Delta and JetBlue are quoting hold times of one hour and 35 minutes and two hours and 16 minutes, respectively.
On Monday, airlines got their first sign of possible relief when the CDC shortened the isolation period for asymptomatic and fully vaccinated individuals who contract COVID-19 from 10 days to five.
United said Friday it would pay pilots triple their salary for picking up extra flights, according to a letter acquired by ABC News. United canceled more than 200 flights on Friday. Spirit Airlines, which had canceled 99 flights as of Friday night, announced it would offer double pay to flight attendants through Jan. 4.
JetBlue CEO Robin Hayes told CNBC Thursday that the new guidelines are definitely going to help, but that "the size of the problem really is just the number of people contracting it."
"Things are likely to get worse before it gets better," he said.
ABC News' Sam Sweeney contributed to this report.