This story was updated on Wednesday, January 11 at 9:46 a.m. EST.
Normal air traffic operations are resuming across the United States following an overnight outage to the Notice to Air Missions system that provides safety info to flight crews, the U.S. Federal Aviation Administration (FAA) says.
The FAA announced that a ground stop had been lifted at around 8:50 a.m. and that operations were resuming gradually.
Earlier this morning, flights were grounded and delayed across the U.S. after the FAA said its Notice to Air Missions, or NOTAM, system had "failed."
Sharing updates via Twitter, the FAA spent the morning performing validation checks and reloading its system, which saw its National Airspace System affected by the glitch.
NOTAM alerts span from mundane information about construction at airports to urgent hazards or malfunctioning equipment.
Thousands of flights impacted
More than 4,500 flights within, to and out of the U.S. were delayed as of around 9:30 a.m. Wednesday, according to flight tracker FlightAware.
The full extent of the delays was not entirely clear, but Toronto Pearson took to Twitter early Wednesday to acknowledge the outage.
"Given an FAA system outage, we advise all U.S.-bound passengers to check the status of their flight before heading to the airport," the airport wrote.
All flights that were in the sky during the outage were still safe to land, the FAA said.
U.S. President Joe Biden instructed the Department of Transportation on Wednesday to conduct a full investigation into the causes of the flight delays.
In a statement posted to Twitter, White House Press Secretary Karine Jean-Pierre said there is no evidence that the outage was caused by a cyberattack.
Air Canada told the Canadian Press on Wednesday that it is not possible to determine the extent of the delays at this point.
The airline is implementing a goodwill policy for affected customers to change their travel plans.
WestJet said six flights were delayed Wednesday morning because of the outage, but no flights were cancelled.