Acts of unlawful interference. These are acts or attempted acts such as to jeopardize the safety of civil aviation and air transport, i.e.:
- unlawful seizure of aircraft in flight,
- unlawful seizure of aircraft on the ground,
- hostage-taking on board aircraft or on aerodromes,
- forcible intrusion on board an aircraft, at an airport or on the premises of an aeronautical facility,
- introduction on board an aircraft or at an airport of a weapon or hazardous device or material intended for criminal purposes,
- communication of false information such as to jeopardize the safety of an aircraft in flight or on the ground, of passengers, crew, ground personnel or the general public, at an airport or on the premises of a civil aviation facility.
Source: ICAO Annex 17: Security
Unlawful interference is considered a serious hazard to aviation because the consequences of such acts may impact not only the aircraft and those onboard but also potentially high number of people or critical installations on the ground. Therefore, a variety of countermeasures have been developed.
Most efforts against acts of unlawful interference are aimed at their prevention.
At national level, each State must establish an aviation security body for the purpose of coordinating security activities between the stakeholders concerned with or responsible for the implementation of various aspects of the national civil aviation security programme. Additionally, aircraft and airport operators are required to establish and maintain a security programme covering their activities. These programs are subject to quality control and regular audits.
Additionally, measures are taken in order to prevent unlawful interference that address specific circumstances, e.g.:
- access control. These include security measures (e.g. perimeter fences, ID systems) that separate the airside of airports and restrict access to security-critical areas, e.g. the apron and the manoeuvring area.
- aircraft security. This includes preventing entry into the aircraft by unauthorized persons and making sure no personal items are left behind by passengers. Another example of these is the rule for a lockable flight deck door that is able to resist penetration by small arms fire and grenade shrapnel as well as complementary procedures that define the circumstances under which the door may be open.
- cabin baggage. An example of this is the hand baggage and passenger screening before departure.
- hold baggage. This baggage is also subject to screening and also operators would not normally transport baggage of a person that is not on board of the aircraft. An exception to the latter is the case where the baggage is declared as "unaccompanied" but in this case it will be subject to additional screening.
- cargo, mail and other goods. Special security procedures are developed in case such goods are to be transported on passenger aircraft.
- special categories of passengers. These include security measures for transporting potentially disruptive passsengers, i.e. persons that are subject of judicial or administrative proceedings. For example, special provisions about the carriage of weapons onboard are defined and also the flight crew must be duly informed about the situation.
Mitigation measures are aimed at reducing the impact of unlawful interference should there be a security breach that would allow such a situation to happen. Examples of such measures are:
- The crew of a flight that has been subject to unlawful interference would try to notify the appropriate ATS unit of the situation using appropriate methods (e.g. call on the frequency, deviation from the current flight plan, transponder code 7500, CPDLC message, etc.). Such actions would be taken if it is considered that they would not exacerbate the situation.
- Air traffic controllers are trained to recognize the signs of possible unlawful interference and to inform the authorities who would trigger appropriate procedures (e.g. military interception). The controller would likely provide increased separation in such situations.
- Military interception is not uncommon when unlawful interference is suspected (or has been confirmed). These missions may vary from information gathering (as for example in the case of B733, en-route, northwest of Athens Greece, 2005) to accompanying the aircraft or forcing it to land. As a last resort there is the option to use weapons against the aircraft subject to unlawful interference although such a decision is only to be made under extreme circumstances.
- On some airports there are parts of the apron designated to be used in case of an aircraft subject to unlaful interferece. These are usually located at a safe distance from the airport critical facilities, other aircraft and passenger terminals and are used when e.g. there is a (suspected) bomb threat.
ICAO Annex 17: Security