Jernnard, who was a ticketed passenger, was wearing a white shirt with an Air France logo and had a black jacket with epaulets on the shoulders, police said. Officer Christine O'Brien said police found him in possession of a counterfeit Air France crew member ID card.
Air France said Jernnard is not one of its employees and was not wearing the airline's uniform.
It's not clear how Jernnard got into the cockpit, but one security expert said he didn't view it as a breach.
Pilots can typically ride for free in the jump seat of another airline, but they must make arrangements ahead of time and their presence would be noted on a passenger manifest. That manifest is reviewed by the pilot before takeoff — meaning that Jernnard didn't have a chance of remaining, said Douglas Laird, former security director for Northwest Airlines.
"The guy can't do any harm sitting up there. He has no access to the controls sitting there. I think the system worked," said Laird, who now runs an airline security consultancy in Reno, Nev.
Police said there's no indication Jernnard meant any harm. A US Airways spokeswoman referred questions to the FBI, which confirmed it is investigating but declined to comment Friday.
O'Brien said Jernnard initially became upset at the gate when he asked to be upgraded to business class.
"The (US Airways) employee gate agent told the male there was no space left in business class. He became irate," O'Brien said.
Jernnard then boarded the plane and made his way to the jump seat.
He was charged with criminal trespass, forgery, records tampering, false impersonation of a person privately employed, and providing false identification to law enforcement. He was jailed on $1 million bail pending a preliminary hearing scheduled for April 5. Federal charges are also expected.
Jernnard is represented by the Philadelphia public defender's office, which did not immediately respond to a request for comment.
In France, police in La Rochelle as well as the national police declined to comment, saying they are not allowed to disclose information about individuals.
Jernnard's stunt mirrored one by con man Frank Abagnale Jr., whose exploits were chronicled in the 2002 hit film "Catch Me If You Can." In the movie, Abagnale, played by Leonardo DiCaprio, is able to make his way into a plane's cockpit, bluffing his way past security and distracting the FBI by donning a pilot's uniform.
Laird said he can recall a few other cases before the Sept. 11 attacks in which civilians talked their way into the cockpit and were not discovered until the planes had actually taken off.
"If you are civilian, you can't pass yourself off as an Air France pilot because within about 30 seconds the pilots go, 'This guy has not a clue,'" Laird said. "It would be like you and I passing ourselves off as surgeons."
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