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Non-Standard Phraseology

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Category: Air Ground Communication Air Ground Communication
Content source: SKYbrary About SKYbrary


Of the many factors involved in the process of communication, phraseology is perhaps the most important because it enables us to communicate quickly and effectively despite differences in language and reduces the opportunity for misunderstanding.

Standard phraseology reduces the risk that a message will be misunderstood and aids the read-back/hear-back process so that any error is quickly detected. Ambiguous or non-standard phraseology is a frequent causal or contributory factor in aircraft accidents and incidents.

International standards of phraseology are laid down in ICAO Annex 10 Volume II Chapter 5 and in ICAO Doc 9432 - Manual of Radiotelephony. Many national authorities also publish radiotelephony manuals which amplify ICAO provisions, and in some cases modify them to suit local conditions.

This article deals with non-standard phraseology, which is sometimes adopted unilaterally by national or local air traffic services in an attempt to alleviate problems; however, standard phraseology minimises the potential for misunderstanding.


Where non-standard phraseology is introduced after careful consideration to address a particular problem, it can make a positive contribution to flight safety; however, this must be balanced with the possibility of confusion for pilots or ATCOs not familiar with the phraseology used.

Non-standard phraseology in Europe

The UK CAA has adopted certain non-standard phraseology designed to reduce the chance of mishearing or misunderstanding RTF communications. This phraseology is not in accordance with ICAO but is based on careful study of the breakdown of pilot/controller communications. Some other European countries have also adopted similar non-standard phraseology.

The following paragraphs taken from the UK Manual of Radiotelephony summarise the main differences.

  • The word ‘to’ is to be omitted from messages relating to FLIGHT LEVELS.
  • All messages relating to an aircraft’s climb or descent to a HEIGHT or ALTITUDE employ the word ‘to’ followed immediately by the word HEIGHT or ALTITUDE. Furthermore, the initial message in any such RTF exchange will also include the appropriate QFE or QNH.
  • When transmitting messages containing flight levels each digit shall be transmitted separately. However, in an endeavour to reduce ‘level busts’ caused by the confusion between some levels (100/110, 200/220 etc.), levels which are whole hundreds e.g. FL 100, 200, 300 shall be spoken as “Flight level (number) HUNDRED”. The word hundred must not be used for headings.
  • Examples of the above are:
    • “RUSHAIR G-BC climb flight level wun too zero.”
    • “RUSHAIR G-BC descend to altitude tree tousand feet QNH 1014.”
    • “RUSHAIR G-BC climb flight level wun hundred.”
    • “RUSHAIR G-BC turn right heading wun wun zero.”

Non-standard North American phraseology

A particular example of non-standard phraseology which is in regular use in North America is the instruction “taxi into position and hold”, (which has the same meaning as the ICAO standard phrase “line up and wait”).This can be confused with the old ICAO phraseology “taxi to holding position” (which means taxi to, and hold at, a point clear of the runway).

Use of this non-ICAO standard phraseology is fail-safe in North America, but in Europe can lead to an aircraft taxiing onto the runway when not cleared to do so. To overcome this problem ICAO has amended its phraseology to "taxi to holding POINT".

Non-standard Phraseology in Abnormal/Emergency Situations

Is is often necessary for pilots and controllers to revert to non-standard phraseology in abnormal and emergency situations. The extent to which this occurrs, and leads to effective communication, will depend upon the quality of the both speech delivery and language proficiency of those involved.

Accidents and Incidents

The following events include "Phraseology" as a contributing factor:

  • A320, en route, north of Marseilles France, 2013 (On 12 September 2013, pressurisation control failed in an A320 after a bleed air fault occurred following dispatch with one of the two pneumatic systems deactivated under MEL provisions. The Investigation found that the cause of the in-flight failure was addressed by an optional SB not yet incorporated. Also, relevant crew response SOPs lacking clarity and a delay in provision of a revised MEL procedure meant that use of the single system had not been optimal and after a necessary progressive descent to FL100 was delayed by inadequate ATC response, and ATC failure to respond to a PAN call required it to be upgraded to MAYDAY.)
  • B735, vicinity London Heathrow UK, 2007 (On 7 June 2007, a Boeing 737-500 operated by LOT Polish Airlines, after daylight takeoff from London Heathrow Airport lost most of the information displayed on Electronic Flight Instrument System (EFIS). The information in both Electronic Attitude Director Indicator (EADI) and Electronic Horizontal Situation Indicators (EHSI) disappeared because the flight crew inadvertently mismanaged the Flight Management System (FMS). Subsequently the crew had difficulties both in maintaining the aircraft control manually using the mechanical standby instruments and communicating adequately with ATC due to insufficient language proficiency. Although an emergency situation was not declared, the ATC realized the seriousness of the circumstances and provided discrete frequency and a safe return after 27 minutes of flight was achieved.)
  • B738/B738, vicinity Queenstown New Zealand, 2010 (On 20 June 2010, a Boeing 737-800 being operated by New Zealand company Pacific Blue AL on a scheduled passenger flight from Auckland to Queenstown lost IFR separation assurance against a Boeing 737-800 being operated by Qantas on a scheduled passenger flight from Sydney to Queenstown whilst both aircraft were flying a go around following successive but different instrument approaches at their shared intended destination. There were no abrupt manoeuvres and none of the respectively 88 and 162 occupants of the two aircraft were injured.)
  • B742 / B741, Tenerife Canary Islands Spain, 1977 (On 27 March 1977, a KLM Boeing 747-200 began its low visibility take-off at Tenerife without requesting or receiving take-off clearance and a collision with a Boeing 747-100 backtracking the same runway subsequently occurred. Both aircraft were destroyed by the impact and consequential fire and 583 people died. The Investigation attributed the crash primarily to the actions and inactions of the KLM Captain, who was the Operator's Chief Flying Instructor. Safety Recommendations made emphasised the importance of standard phraseology in all normal radio communications and avoidance of the phrase "take-off" in ATC Departure Clearances.)
  • A320, en-route, Denver CO USA, 2009 (On 21 October 2009, an Airbus 320-200 being operated by Northwest Airlines on a scheduled passenger flight from San Diego to Minneapolis-St Paul, with the Captain as PF, overflew its destination at cruise level in VMC at night by more than 100 nm, after the two pilots had become distracted in conversation and lost situational awareness. They failed to maintain radio communications with a series of successive ATC units for well over an hour. After a routine inquiry from the cabin crew as to the expected arrival time, the flight crew realised what had happened and re-established ATC contact after which the flight was completed without further incident.)

Further Reading

AGC Safety Letters:

EUROCONTROL Action Plan for Air-Ground Communications Safety: