Travelers across the country are facing mass flight delays today after a computer problem at the Federal Aviation Administration crippled flight plans.
The FAA has two systems that process flight plans -- one located in Atlanta and another in Salt Lake City. The Atlanta system went down at 1:30 p.m., and all flight plans are now being handled out of Salt Lake City.
As a result, delays of up to 90 minutes are already surfacing at several airports and more could pile up at airports across the country.
"Currently my flight is delayed 25 minutes," one passenger said. "Generally that's optimistic. I expect that it will be delayed further."
"This was a failure mode we have not seen before," said FAA chief operating officer Hank Krakowski this afternoon.
According to the FAA, about 6,500 airplanes are in the FAA system. The aviation agency has not said how many were in the sky and how many were on the ground when the problem occurred.
Krakowski said most of the delays were happening in the eastern portion of the United States, with none reported west of Dallas or Chicago. With a heavy volume of air traffic converging on the East Coast, delays could spread depending on how much time it takes to iron out the problem.
Chicago's Midway Airport and Atlanta's Hartsfield-Jackson were still experiencing problems late in the day, though part of the problem in Atlanta was due to weather, according to the FAA.
In Chicago, the city's aviation department is recommending that travelers check the status of their flights before heading to the airport.
At the City of Chicago's Department of Aviation, media relations coordinator Gregg Cunningham reported this afternoon that outbound flights from Midway were delayed by 90 minutes.
At Reagan National airport near Washington, D.C., no major delays were apparent this afternoon. Ticket counters and screening areas did not have out of the ordinary lines, and just a handful of flights were delayed by 15 minutes or more.
Both Atlanta and New York are experiencing weather delays.
While the FAA said it can still see all the planes in the sky and it can communicate with all the planes in flight, the system will still experience delays. The computer problem will not affect safety, according to the FAA.
The FAA said this is not a radar issue.
Still, airplanes can't take off without flight plans. Instead of having two facilities processing those plans, only one is currently up and running.
"They're working with an antique system that's overloaded by high traffic growth," said Richard Aboulafia, commercial aviation analyst.
The FAA is focusing on clearing the backlog from the planes that were in the system when it failed. There is not yet an estimate on when the problem in Atlanta will be fixed.
In Salt Lake City, the system still accepting and processing flight plans, operators were working "fast and furiously," according to the FAA. Airline dispatchers are manually inputting flight plans instead of the plans automatically entering into the system.
ABC News' Dennis Powell and Matt Hosford contributed to this report.