Thousands of flight delays and cancellations were widespread across the United States early Wednesday after a computer glitch led to a grounding order for all departing aircraft by the Federal Aviation Administration.
The FAA was working for several hours to restore what is known as the Air Mission Notification System.
Before beginning a flight, pilots must consult NOTAMs, or Notices to Air Missions, which list potential adverse impacts on flights, from runway construction to the possibility of icing. The system used to be telephone-based, with pilots calling dedicated flight service stations for information, but has now moved online.
While the White House initially said there was no evidence of a cyber attack, U.S. President Joe Biden said "we don't know" and told reporters he ordered the Department of Transportation to investigate the cause of the outage.
The FBI did not immediately respond to a request for comment.
The suspension order was lifted just before 9 a.m., but delays and cancellations are expected to increase. Boarding gates at major airports are full of planes that were ordered to stay on the ground for hours.
More than 21,000 flights were scheduled to take off in the U.S. today, mostly domestic travel, and about 1,840 international flights were expected to fly to the U.S., according to aviation data firm Cirium.
Nearly 5,000 flights were delayed and nearly 900 were canceled around 10 a.m.
The FAA's suspension order affected nearly all cargo and passenger airline flights.