After a half hour, maintenance workers opened the door and were stunned to find him inside.
"They said, 'Where's your badge?''' Wagner said. "I said, 'Dude, I don't work here, I'm a passenger on this airplane.' And he said 'Hold on, hold on.' He didn't believe it."
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"It's obvious in this case that the crew exiting the airplane did not do a sweep,'' aviation expert Michael Boyd told TODAY. "Whatever they say, you can't miss this."
United offered him $250 and a hotel room in Houston for the night, according to Wagner. ExpressJet, the company that operated the United flight, issued a statement to TODAY.
"ExpressJet is investigating to determine how this occurred. We sincerely apologize for the inconvenience this caused for the passenger."
Wagner was puzzled as to why no one tried to wake him.
"I just don't know how it happened, I really don't,'' he said. "I mean, passengers get off, you'd think somebody would have rubbed me or pushed me and said, 'Hey buddy, we're here.'''
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Wagner is set to return to Louisiana on United next week. This time, he said, he'll get a good night's sleep before the flight.
—By Scott Stump, TODAY contributor