Thousands of flights across the U.S. were canceled or delayed Wednesday after a government system that offers safety and other information to pilots broke down, stranding some planes on the ground for hours.

The Federal Aviation Administration had ordered airlines to pause all domestic departures until 9 a.m. after its Notice to Air Missions system - which sends pre-flight safety alerts to pilots - failed.

The White House said there was no evidence that a cyberattack triggered the outage, which upended travel plans for millions of passengers. President Joe Biden said he directed the Department of Transportation to investigate.

Islip's MacArthur Airport reported many arrival and departure delays Wednesday because of the FAA computer outage. However, flights scheduled for midday and this afternoon were still on time. Airlines are urging passengers to check their flight status before heading out.

Merrick resident Liz Condon's flight from Fort Lauderdale to Ronkonkoma was one of more than 1,000 flights canceled.

"I would rather be home today and I'm sure it changed a lot of people's plans," Condon said.

Other travelers at MacArthur Airport say they canceled out of fear of what exactly was going on.

Professor of aviation at Farmingdale College Michael Canders says the system failure sends a clear signal to the FAA.

"This may be a good heads up for the FAA to maybe update their technology for this system," Canders said.

Experts say planes that were in the air when the FAA called for a ground stop were not affected by the computer glitch and were safe since planes already in flight were guided by air traffic controllers.

The agency said normal air traffic operations were resuming gradually across the U.S.

Transportation Secretary Pete Buttigieg said on Twitter that he had ordered an "after-action process to determine root causes and recommend next steps."