A U.S. Airways employee was being questioned by authorities this morning after a bag containing an unloaded gun apparently circumvented security and made it onto a plane at Philadelphia International Airport, police said.

A passenger waiting to board Flight 1195, destined for Phoenix, noticed another passenger handing a carry-on bag directly to the airline employee, said Officer Christine O'Brien, a Philadelphia police spokeswoman.

The bag was not sent through normal secuity screening, O'Brien said, making the waiting passenger suspicious. The passenger alerted officials with the Transportation Security Administration.

A TSA employee boarded the plane, located the suspect bag in an overhead compartment, and found that it contained an unloaded handgun, O'Brien said.

The incident took place at about 7:40 a.m., she said.

The owner of the bag and the U.S. Airways worker were being questioned this morning, police said.

The flight, which was originally scheduled to depart at 7:10 a.m., was delayed almost four hours, finally taking off shortly after 11.

Instead of arriving in Phoenix at shortly after 9 a.m., it was scheduled to reach Phoenix after 1 p.m., according to USAir's website.

Spokespersons for U.S. Airways and the TSA declined to comment on specifics of the incident, saying the FBI had taken over the investigation.

"Safety and security is our first and foremost priority in everything we do," Morgan Durrant, senior manager of corporate communications for the airline, said in an e-mailed statement. "We are cooperating with investigators fully and take security considerations very seriously. Further comment right now is not appropriate out of respect to the ongoing investigation."