The Federal Aviation Administration (FAA) blamed a corrupted database file for a system outage on Wednesday morning, but many questions still remain as airlines deal with the fallout from thousands of delayed and canceled flights.

The FAA ordered airlines to temporarily halt all domestic departures on Wednesday morning as it worked to address a problem with a system that notifies pilots about real-time flight hazards and cautions.

The agency lifted the ground stop after about an hour and a half, but the impacts continued throughout the day, with more than 9,900 U.S. flights delayed and another 1,300 canceled by Wednesday night, according to the flight tracker FlightAware.

Here’s what we know so far:

System initially crashed on Tuesday

The FAA’s Notice to Air Missions (NOTAM) system suffered an outage around 3:30 p.m. on Tuesday, leading officials to temporarily move to a backup system, Transportation Secretary Pete Buttigieg told reporters on Wednesday, per The Washington Post. 

However, ongoing concerns about the accuracy of information coming from the system reportedly led FAA officials to launch a “complete reboot” of the system at around 5 a.m. on Wednesday. 

The FAA ordered the ground stop at 7:21 a.m. as officials remained unsure about whether the system was functioning correctly despite the reboot. Domestic flights were allowed to begin taking off again around 9 a.m. once the issue was resolved.

The agency announced on Wednesday night that the outage was likely the result of a “damaged database file.”

“The FAA is working diligently to further pinpoint the causes of this issue and take all needed steps to prevent this kind of disruption from happening again,” the agency said in a statement.

Airlines scramble to catch up

Thousands of U.S. flights were delayed or canceled in the wake of the ground stop on Wednesday, leaving airlines scrambling to catch up. 

More than half of flights from three major U.S. airlines — Southwest, American and United — were delayed on Wednesday. Delta, the last of the “Big Four” airlines, saw about 40 percent of its flights delayed.

Another 10 percent of Southwest’s flights were canceled, as were seven percent of American’s flights. United and Delta were both able to avoid substantial cancellations, cutting 4 percent and 2 percent of flights, respectively.

All four airlines have said they are offering travelers some form of waiver to rebook flights if needed. Those who had their flights canceled — and, in some cases, those who simply no longer wished to travel — can request refunds through the airlines as well.

It was unclear Wednesday night if delays from the outage would continue into Thursday.

Delta said in a statement, “While potential for additional delays and cancels continue, Delta expects minimal residual impact, if any, on Thursday.”

The other major airlines did not respond to questions about continued delays.

Buttigieg on Wednesday afternoon promised to figure out what went wrong and fix the problem.

“With a government system, we’re going to own it, we’re going to find it, and we’re going to fix it,” Buttigieg told reporters.