Radio Discipline

Radio Discipline


Communication between pilots and air traffic controllers is a process that is vital for the safe and efficient control of air traffic. Pilots must report their situation, intentions and requests to the controller in a clear and unambiguous way; and the controller must respond by issuing instructions that are equally clear and unambiguous. The process of communication is important and must be successful even in the most difficult conditions. Good radio discipline is essential to this process.

Aspects of Radio Discipline


Poor radio discipline is the most common cause of breakdown in the RTF communication process.

Typical Scenarios

  • Not listening out before transmitting. An ATC clearance for another aircraft is read back incorrectly but the error is not appreciated by ATC because of interference from the simultaneous initial call.
  • Non-standard phraseology. The pilot of Rushair 1234 requests descent clearance as follows: “34, request FL120”. The ATCO mistakes the caller for Jetair 314 and responds: “314 descend FL120”. Rushair takes this clearance as intended for him and a level bust results.
  • Message format and content. The ATCO issues a clearance: “Rushair 1234, climb FL240 heading 260”. The pilot climbs to FL260.
  • Language. The ATCO clears a locally-based aircraft to climb using the local language. The clearance creates a conflict with another flight whose pilots do not undestand the local language and are thus unaware of the impending circumstance. Loss of separation results.
  • Timeliness of communication. A pilot about to commence an approach to a runway is instructed to change to the parallel runway. The clearance is issued too late for the pilots to carry out a thorough re-brief but they proceed anyway having failed to assimilate the go-around procedure for this runway.
  • Read-back/hear-back. The pilot mis-hears a clearance but instead of reading the clearance back responds “Roger”. ATC do not challenge this response and a level bust results.
  • Inappropriate use of the frequency. An ATSB Study of congestion on GND frequencies contains examples of this problem (See: Further Reading).

Related Accidents and Incidents

On 3 May 2017, an Airbus A330 and an Airbus A319 lost prescribed separation whilst tracking in opposite directions on a radar-controlled ATS route in eastern Myanmar close to the Chinese border. The Investigation found that the response of the A330 crew to a call for another aircraft went undetected and they descended to the same level as the A319 with the lost separation only being mitigated by intervention from the neighbouring Chinese ACC which was able to give the A319 an avoiding action turn. At the time of the conflict, the A330 had disappeared from the controlling ACCs radar.

On 4 April 2016, a Boeing 737-800 crew taking off in normal night visibility from Jakarta Halim were unable to avoid an ATR 42-600 under tow which had entered their runway after ambiguity in its clearance. Both aircraft sustained substantial damage and caught fire but all those involved escaped uninjured. The Investigation concluded that contributory to the accident had been failure to use a single runway occupancy frequency, towing of a poorly lit aircraft, the potential effect on pilot detection of an obstruction of embedded approach lighting ahead of the displaced landing threshold and issues affecting controller traffic monitoring effectiveness.

On 17 August 2016, a Fokker F50 crossed an active runway at Adelaide ahead of an A320 which was about to land after both its pilots and the controller involved had made assumptions about the content of radio transmissions they were aware they had not fully heard. The Investigation found that the A320 crew had responded promptly to the potential conflict by initiating a low go around over the other aircraft and noted that stop bars were not installed at Adelaide. In addition, aircraft taxiing across active runways were not required to obtain their crossing clearances on the runway control frequency.

On 3 October 2013, a vehicle entered an active runway without clearance after partial readback of a potentially confusing clearance was not challenged by the controller. A different controller then cleared a Boeing 777-300 to land without taking all available action to ensure that the runway was clear. The aircraft crew saw the vehicle near the edge of the runway after touchdown and manoeuvred their aircraft away from it, although the aircraft wing still passed over it. At the time of the incident, vehicles with clearance were permitted to cross red stop bars, a policy which has since been changed.

On 13 April 2007 in day VMC, an Air France A320 departing Sofia lined up contrary to an ATC Instruction to remain at the holding point and be ready immediate. The controller did not immediately notice and after subsequently giving a landing clearance for the same runway, was obliged to cancel it send the approaching aircraft around. An Investigation attributed the incursion to both the incorrect terminology used by TWR and the failure to challenge the incomplete clearance read back by the A320 crew.

Contributory Factors


Related Articles

Further Reading

AGC Safety Letters

EUROCONTROL Action Plan for Air-Ground Communications Safety:


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