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Military Interception Signalling

Military Interception Signalling is defined as “Signals used for communication between intercepting military aircraft and the intercepted aircraft”

 Military aircraft are tasked to intercept unknown aircraft, aircraft which are not in communication with the appropriate ATC agency, and aircraft which are not responding to ATC or have departed from clearance.

A civilian airliner is most likely to be intercepted if it has lost communications with ATC or strays into airspace without appropriate diplomatic clearance and without speaking to the appropriate controlling authority.

Since the events of 11 September 2001, military interception of aircraft which are not responding to communications with ATC has become commonplace. Furthermore, because of the security issues, such intercepts are potentially hazardous and it is important that crews know what to expect when intercepted and are aware of the signals used by military aircraft and how to respond.

Interception and ACAS

If the intercepting aircraft is/are ACAS equipped then the first indication the intercepted aircraft will have of the interception will be on TCAS (expect spurious commands). Upon acquiring the interceptors visually, the intercepted aircraft should set the TCAS to TA.

The Interception

The military interceptors will approach the aircraft from behind.


If there are 2 aircraft, the second will usually adopt a surveillance position while the lead aircraft moves up closer to identify the aircraft.

If the interceptors are not TCAS equipped then the first notification of interception may well come from passengers via the cabin crew.

The intercepting aircraft will slowly move closer but no closer than is necessary to identify the aircraft.

The interceptor aircraft will be careful not to alarm the crew and passengers and will manoeuvre slowly and deliberately. Expect the lead aircraft to adopt a position slightly ahead, higher and to the left.


In IMC or at night, the intercepting aircraft will approach establish themselves in a radar trail comfortably behind the intercepted aircraft and will maintain a safe vertical separation.

Actions on Interception

The flight crew of the intercepted aircraft should follow the instructions given by the interceptor, interpreting and responding to the visual signals (see paragraph on Interception signals below).

The flight crew should notify the appropriate ATC unit and attempt to establish radio communication with the interceptor on 243.0 MHz or 121.5 MHz, giving the identity and position of the aircraft and the nature of the flight. The flight crew should then Squawk emergency (7700) unless otherwise instructed.

If the intercepted aircraft receives intructions from any source which conflict with the instructions given by the intercepting aircraft, they should seek clarification but continue to comply with the instructions given by the intercepting aircraft.

Military Aircraft Performance

The intercepted aircraft crew can expect to see different drag devises deployed by the interceptor as it stabilises its speed and position. Turboprops should anticipate the need to maintain an IAS above 200 kts so as not to cause the fighter any difficulty in maintaining formation.

Signals initiated by intercepting aircraft and responses by intercepted aircraft
Series INTERCEPTING Aircraft Signals Meaning INTERCEPTED Aircraft Responds Meaning
1 DAY-Rocking wings from a position slightly above and ahead of, and normally to the left of, the intercepted aircraft and, after acknowledgement, a slow level turn, normally to the left, on to the desired heading.NIGHT-Same and, in addition, flashing navigational lights at irregular intervals.NOTE 1-Meteorological conditions or terrain may require the intercepting aircraft to take up a position slightly above and ahead of, and to the right of, the intercepted aircraft and to make the subsequent turn to the right.

NOTE 2-If the intercepted aircraft is not able to keep pace with the intercepting aircraft, the latter is expected to fly a series of race-track patterns and to rock its wings each time it passes the intercepted aircraft.

You have been intercepted. Follow me. AEROPLANES:DAY-Rocking wings and following. NIGHT-Same and, in addition, flashing navigational lights at irregular intervals.HELICOPTERS: DAY or NIGHT-Rocking aircraft, flashing navigational lights at irregular intervals and following. Understood, will comply.
2 DAY or NIGHT-An abrupt break-away maneuver from the intercepted aircraft consisting of a climbing turn of 90 degrees or more without crossing the line of flight of the intercepted aircraft. You mayproceed. AEROPLANES:DAY or NIGHT-Rocking wings.HELICOPTERS: DAY or NIGHT-Rocking aircraft. Understood, will comply.
3 DAY-Circling aerodrome, lowering landing gear and overflying runway in direction of landing or, if the intercepted aircraft is a helicopter, overflying the helicopter landing area.NIGHT-Same and, in addition, showing steady landing lights. Land at this aerodrome. AEROPLANES:DAY-Lowering landing gear, following the intercepting aircraft and, if after overflying the runway landing is considered safe, proceeding to land.NIGHT-Same and, in addition, showing steady landing lights (if carried).

HELICOPTERS: DAY or NIGHT-Following the intercepting aircraft and proceeding to land, showing a steady landing light (if carried).

Understood, will comply.


Signals initiated by intercepted aircraft and responses by intercepting aircraft
Series INTERCEPTED Aircraft Signals Meaning INTERCEPTING Aircraft Responds Meaning
4 DAY or NIGHT-Raising landing gear (if fitted) and flashing landing lights while passing over runway in use or helicopter landing area at a height exceeding 300m (1,000 ft) but not exceeding 600m (2,000 ft) (in the case of a helicopter, at a height exceeding 50m (170 ft) but not exceeding 100m (330 ft) above the aerodrome level, and continuing to circle runway in use or helicopter landing area. If unable to flash landing lights, flash any other lights available. Aerodrome you have designated is inadequate. DAY or NIGHT-If it is desired that the intercepted aircraft follow the intercepting aircraft to an alternate aerodrome, the intercepting aircraft raises its landing gear (if fitted) and uses the Series 1 signals prescribed for intercepting aircraft.If it is decided to release the intercepted aircraft, the intercepting aircraft uses the Series 2 signals prescribed for intercepting aircraft. Understood, follow me.  

Understood, you may proceed.

5 DAY or NIGHT-Regular switching on and off of all available lights but in such a manner as to be distinct from flashing lights. Cannot comply. DAY or NIGHT-Use Series 2 signals prescribed for intercepting aircraft. Understood.
6 DAY or NIGHT-Irregular flashing of all available lights. In distress. DAY or NIGHT-Use Series 2 signals prescribed for intercepting aircraft. Understood. 


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