Unlawful Interference: Guidance for Controllers

Unlawful Interference: Guidance for Controllers


This article provides guidance for controllers on what might be expected from a hijacked aircraft. It details some of the considerations which will enable the controller, not only to provide as much support as possible to the aircraft concerned, but also to maintain the safety of other aircraft in the vicinity and that of the ATC service provision in general.

Useful To Know

Unlawful interference (aircraft hijacking) has been recognized as a considerable danger to the safety of aviation. The international community has witnessed the disastrous potential of such acts in a number of accidents. As early as 1969, the Tokyo Convention on Offences and Certain Other Acts Committed On Board Aircraft entered into force and was ratified by 185 countries. The act provided the pilot in command with some special powers to counteract the commitment of unlawful acts.

Several other documents have come into force over subsequent years. As individuals or groups used aircraft hijacking to pursue political, economic or individual goals, so governments and the aviation industry upgraded security regulations and requirements. More recent incidents brought changes to aircraft design, some of which were publicly announced and others logically concealed from public view.


Acts of unlawful interference do not follow any specific scenario - sometimes even the confirmation of that such action is in progress proves to be a challenge. The outcome and the effects might vary significantly depending on the situation:

  • Hindered or complete loss of communication with the crew;
  • Immediate descent and landing, if cockpit security and safety of passengers is not affected;
  • Single or multiple, unannounced, flight path deviations - vertical/horizontal;
  • Diversion to an airport, not listed in the flight plan;
  • Possible on-board bomb threat;
  • Selective compliance to instructions;
  • Runway blockage after landing;
  • Medical help might be required.

Anticipated Impact On Crew

In all cases, the hijacking dramatically increases the stress level for the entire crew. Amongst other implications are:

  • Possible injuries to, or death of, one or more crew members;
  • Injuries to, or death of, passengers or hijackers;
  • Incompatibility between hijacker demands and flight safety;
  • Complications due to diversion from planned route or altitude - fuel deficiency, Airspace Infringement, landing at unsuitable airport;
  • Prolonged hostage situation with additional complications such as lack of water, food and medical supplies.

Suggested Controller's Actions

Best practice embedded in the ASSIST principle could be followed: (A - Acknowledge; S - Separate, S - Silence; I - Inform, S - Support, T - Time)

A - exercise utmost caution when acknowledging the observed crew’s actions, do NOT ask for the crews’ intentions

S - separate the aircraft from other traffic, prioritise it for landing (allow long final if requested), keep the active runway clear of departures, arrivals and vehicles

S - silence the non-urgent calls (as required) and use separate frequency where possible

I - inform the airport emergency services and all concerned parties according to the local procedures

S - support the flight being hijacked with any information requested and deemed necessary (e.g. type of approach, runway length and aerodrome details, etc.)

T - provide time for the crew to assess the situation, don’t press with non-urgent matters

What to Expect

  • Broken or incomplete communication
  • Sudden course changes
  • Non-adherence to instructions

What to Provide

  • Increased separation
  • Any required information about the airport for landing
  • Compliance with pilot’s requests as far as possible
  • All available information for the sector, the affected aircraft is about to enter


  • Additional specific information regarding response, counter-measures and local protocols should be sought via the local ANSP sources of information. Local procedures addressing such events and the State’s law enforcement agencies should also be consulted.

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