The Federal Aviation Administration (FAA) defines a threat as an attempt by an airline passenger to interfere with a flight crew. Incidents are categorized under four threat levels that escalate from disruptive behavior to violence.
The first threat level involves suspicious or threatening behavior. Next is physical aggression, followed by a credible terrorist threat or hijacking attempt. The most serious threat is a breach or attempted breach of the flight deck.
The threats were defined to prevent air-related terror attacks by training flight crews on how to manage and report incidents of passenger interference with crew members.
The goal of immediately reporting instances of passenger interference is to determine whether the event is part of larger, coordinated terrorist attack.
Flight crews must report any incident to the nearest air traffic control facility. The report must contain the threat level, time, whether priority handling is necessary and the flight deck is secure.
The Aviation Safety Reporting System has found that most threats to commercial airline safety are caused by drunk or mentally unstable passengers who assault or intimidate the flight crew.
