A crew member recognized and questioned a person from the employee shuttle and determined the passenger was not an American Airlines employee, causing Flight 136 to Heathrow to be diverted to the New York airport.
The flight attendant on the plane apparently became suspicious of a male passenger because there was "some confusion as to whether the man was properly security screened" before boarding at Los Angeles International Airport, a law enforcement official said.
Authorities were questioning the passenger Thursday morning at Kennedy International Airport, said the official, who spoke on condition of anonymity because the person was not authorized to speak to the media.
Homeland Security Secretary Michael Chertoff said the incident may have been a miscue.
"The individual in question was, in fact, an employee who was traveling in a private capacity," Chertoff told a cable news network, saying he had gotten information from airline representatives. "It may very well turn out that this is nothing more than a misunderstanding with an employee."
The scare followed on the heels of a new threat assessment and Chertoff's comment earlier this week that he had a "gut feeling" the United States faced a heightened risk of attack this summer. The new threat assessment from U.S. counterterrorism analysts said Al Qaeda restored its operating capabilities to a level unseen since the months before the Sept. 11, 2001, attacks.
The diverted plane, carrying 230 passengers, landed in New York about 3:30 a.m., said Alan Hicks, a spokesman for the Port Authority of New York and New Jersey, which operates the airport. He said the agency was told about an hour earlier that Flight 136 was being diverted.
The plane’s cabin was to be searched and passengers were to be screened and reassigned flights at JFK.
The plane was still at the airport later Thursday morning, Hicks said.
The Department of Homeland Security told FOX News that the situation had been resolved and that the passenger had a valid round-trip ticket purchased on April 19.
A message left with an after-hours contact number at AMR Corp.'s American Airlines in Fort Worth, Texas, was not immediately returned.
The Associated Press contributed to this report.