Thousands of flights across the country were canceled or delayed early this morning after the Federal Aviation Administration’s real-time safety communication system, known as NOTAM, went down overnight. The system is used to tell pilots and air traffic controllers about things like “closed runways, large flocks of birds, a plume of volcanic ash, ice on a runway” and more, according to NPR.

NPR reports more than 4,300 flights within, into or out of the U.S. had been delayed and more than 750 others canceled as of 9 a.m.

The system went down at about 6:30 a.m. and was back up by 9:00 a.m. Officials are still investigating the cause of the outage.

https://twitter.com/FAANews/status/1613171400801394688

All major airports in the country have been affected by the outage, but disruptions are heaviest in the eastern half of the country. Flight delays and cancelations at D.C.’s three largest airports are comparable to other major airports of a similar size. Locally, more than 70 flights out of the region’s three airports are canceled today. More than 300 were delayed this morning.

Reagan National had about 10% of its flights canceled and BWI saw nearly half its flights delayed.

Here are the stats as of 11 a.m., per FlightAware.com.

Reagan National Airport

49 flights canceled (10%)

128 flights delayed (28%)

American Airlines and its subsidiaries have the most delays and cancellations.

At Dulles International Airport

8 flights canceled (2%)

62 flights delayed (17%)

United Airlines has the most delays at Dulles.

At Baltimore/Washington International Airport

19 flights canceled (6%)

128 flights delayed (44%)

Southwest Airlines has the most delays at BWI.

All three local airports have resumed service and urged travelers to check with their airlines for updates on their scheduled flights.

This is the second major air traffic disruption in the last month. In late December, Southwest Airlines had staffing and computer issues that conspired with bad weather, leading to thousands of flights being cancelled and delayed around the country.