MaxSez. The Police Officer was in violation of Federal Law. USC Title18#92C, A&B.Off-duty municipal or State police officers are not allowed to carry firearms onto a commercial airplane.
In Summery: In order to fly while armed, an officer’s employing agency must submit an armed travel request/notification through the National Law Enforcement Telecommunications System (NLETS) computer network. The message must include the name of the officer, the destination of the flight, and the reason why the officer needs to have his/her firearm available immediately upon landing (prior to being able to retrieve checked luggage). This might include picking up a prisoner at the destination airport, being involved in a surveillance operation while following a suspect on the airplane to the destination, or as part of a special security detail for a person who is traveling. All of these situations would be considered “on-duty,” so off-duty officers are bound by the same constraints as any other member of the traveling public.
Some Federal officers may be required to be armed, even while traveling off-duty, so they may be able to fly armed even while not on duty. The Federal agency, however, must have a general policy requiring its officers to be armed.