Airline security refers to a set of procedures as well as infrastructure designed to avoid security problems aboard aircraft. A related area is the much more widespread concept of airport security. In fact, traditionally in most countries, security for air travel has been entirely based in airports. An obvious exception, historically speaking, has been security measures aboard aircraft of the Israeli El Al airline. These include undercover armed security guards, as well as secure cargo holds.
The suggestion of increasing security actually aboard aircraft arose after the terrorist attacks of September 11, 2001. A controversial decision in the United States has been to allow pilots to carry handguns for personal safety, and allow flights to carry armed "sky marshals". One suggestion, which may not be accurate, concerning the discharge of firearms inside aircraft, is that the depressurization caused by bullet holes will cause the aircraft to explode. As well as proposals to strengthen airport security, United States Congress spent $250 million to reinforce the cockpit doors on commercial aircraft. However, most of the time these cockpit doors remain open due to restricted ventilation in the cockpit.