DFW AIRPORT — We now know a software glitch — a "system failure" — caused Tuesday's shutdown of American Airlines.
The system had recovered by Tuesday night, but hours earlier, the tarmac at Dallas/Fort Worth International Airport was littered with jets delayed for hours when the carrier's computer network went offline.
Passengers crammed inside airport terminals in Texas and around the nation, waiting and hoping to re-book canceled flights.
"We have no idea when we're going to get home," said passenger Christine Barrow.
The backlog was slowly unwinding on Tuesday evening. American canceled 260 flights at DFW — 14 percent of the airline's regular schedule.
American CEO Tom Horton bypassed reporters and issued a statement on YouTube, blaming a software problem for the sudden shutdown.
"We don't like to let you down. Again, we're very sorry for that," Horton said in the video. "As you's imagine, we do have redundancies in our systems, but unfortunately — in this case — we had a software issue that impacted both our primary and backup systems."
Nationwide, American was forced to cancel more than 700 flights, with hundreds more delayed.
Aircraft couldn't take off. And many couldn't even taxi to gates that were occupied by other planes.
Reservations couldn't be accessed; agents were unable to help passengers.
"They told us not to check our bags just yet because they weren't sure they would be able to find our bags later," Barrow said.
Paper signs were affixed to blacked-out computer message boards at one DFW gate.
American's problems so far-reaching, it came as a surprise to cyber security consultant Bill Morgan.
"It's a pretty mature company to have something that large happen," he said. "For something this systemic to occur means there were compromises in many different areas."
Many passengers connected to Facebook, Twitter and Instragram to vent their frustration.
American was tweeting apologies every minute to weary passengers who were coping with delays long after the computer problem was fixed.
"Somebody needs to be calling the head of American Airlines," one woman said.
It remained unclear late Tuesday what triggered the problem. The airline made a point of saying the disruption was not related to Monday's attacks in Boston.
American promised the delays should be largely solved by Wednesday.