A flight from Los Angeles to London was diverted to New York City's JFK airport after the crew reported a suspicious passenger, US officials have said.
Police boarded American Airlines Flight 136 after it made an emergency landing at 0352 (0752 GMT) and detained a man of Middle Eastern descent, CNN TV said.
US Homeland Security Secretary Michael Chertoff said the man was an employee who was flying in a private capacity.
Mr Chertoff told CNN it may have simply have been a "misunderstanding".
"I think the good news here, of course, is an alert crew sees something that's anomalous or seems questionable and they take action," he said.
According to Homeland Security official, the flight from Los Angeles LAX airport to London Heathrow was diverted at 0153 (0553 GMT) while it was over Newfoundland because of the questionable boarding circumstances of a passenger.
A flight attendant was reportedly concerned that a passenger had used the employee shuttle bus at LAX to board the plane and bypass security controls.
The pilot then diverted the flight to JFK airport, telling passengers the plane needed to refuel.
The plane landed without incident and the man was taken off by security officials.
However, after questioning, it emerged the man was an American Airlines employee who had purchased a legitimate return ticket to London.