(NewsNation) — The weather is good. The plane is at the gate. The flight crew is ready. But flights are still getting delayed and even canceled.

Pilot shortages are part of the problem, but now, a shortage of air traffic controllers has travelers facing a new disruption at the airport.

“I didn’t know … until after I landed, that was the reason. That is a little scary. We had to circle for an hour,” said air traveler Nestle Danisman.

On Sunday, more than 9,000 flights were delayed and 800 were canceled. That’s about 20% of all flights.

And the shortage of air traffic controllers is becoming more common, according to Dennis Tajer, spokesman for the Allied Pilots Association.

In a statement to NewsNation, the Federal Aviation Administration said, in part:

“The FAA does not have a system-wide air traffic controller shortage. Numerous factors are contributing to air travel delays and cancellations in Florida. The number one cause for delays and cancellation of flights by airlines is convective weather in Florida. Second is demand for travel to Florida.”

But an air traffic hub in Jacksonville, Florida, has seen shortages causing delays. Pilot and airline crew shortages can make a small air traffic control delay into a big problem because crews “time out” and can’t keep working. A half an hour delay can turn into a cancellation because pilots and crew are already spread so thin.

“If you are operating at the maximum with very little buffer, you are going to find flights canceling that would not normally cancel because the pilots have a maximum of flight and on duty” time, Tajer said.

According to The Points Guy, the shortage of controllers has been ongoing, following a wave of retirements. It takes years to properly train an air traffic controller and the pandemic has affected the supply of new controllers.

This time of year can be especially difficult for controllers in Florida and the southeast because of thunderstorms and other extreme weather.

“The weather issues and resulting downline impacts were exacerbated by staffing shortages at the Jacksonville Air Traffic Control Center, which controls airspace over the northern two-thirds of Florida,” Frontier CEO Barry Biffle said during his company’s first-quarter earnings call.

Experts don’t expect airline staffing problems to get better anytime soon, predicting relief is at least a year away.

Editor’s Note: This story has been updated with a statement from the FAA.