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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, ICAO Doc 4444 PANS-ATM Chapter 12 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
Regulation 2016/1185 introduces some deviations from the standard ICAO phraseology at EU level:
- Flight levels which are whole hundreds (e.g. FL 100, FL 200, FL 300, etc.) are to be pronounced as "Flight level (number) hundred".
- Altimeter setting of 1000 hPa is to be pronounced as "One thousand".
- Transponder codes containing whole thousands are to be pronounced as "(number) thousand".
- For transfers of communication within one ATS unit, the call sign of the ATS unit may be omitted, when so authorised by the competent authority.
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.
Neither Standard, Nor Approved
Sometimes controllers and pilots use phraseology that is neither standard, nor approved by a national civil aviation authority. The reasons for this may be various, e.g. poor knowledge or training, phrase that is rarely used, personal experience or preference, etc. The main difference betweeen approved and non-approved phraseology is that the latter has not undegrone any safety impact assessment.
There are several major risks associated with such phraseology:
- The other party may not hear the message correctly. When dtandard phraseology was developed, special attention was given to choosing words and phrases that sound distinctly different and therefore cannnot be confused under any readability circumstances. When replacing standard phraseology with their own people do not perform thorough research as to whether their custom phrase may sound similarly to another one.
- The other party may not understand the message. This may be due to e.g. using phrasal verbs or other words that are not commonly known. The different levels of knowledge of the English language contributes to this as well.
- The message may be ambiguous, i.e. the transmitting person may mean one thing and the other one may understand something else, as was the case with the vehicle incursion at Perth in 2012 or in an incident at Toronto in 2016.
Examples of unofficial "phraseology" (the list is not exclusive):
- Ten/eleven thousand (instead of one zero thousand or one one thousand). This was considered by the investigation to be the cause of an incident in 2011
- Read you five by five (or any other X by Y combination) instead of Read you (number)
- ARL10 pronounced as Airline ten (instead of Airline one zero)
- Light chops, smooth ride, what's the ride, instead of phrases containing the word turbulence
- Affirmative instead of affirm (note that affirmative may, under certain low-readability circumstances, be confused with negative due to having the same ending)
- Double and tripple (instead of pronouncing each digit separately)
- Keep heading, speed, etc. (instead of continue or maintain)
- Up and down instead of climb and descend
- Pronouncing 9 as nine instead of niner which may lead to confusion with 5
- Amending clearance staring with While we wait (which can be undestood as line up and wait), which was considered as a contributor in a runway incursion event
- Using take-off instead of departure in situations where no take-off clearance is issued or cancelled. This has caused a number of occurrences, e.g. an accident in 1977 and an incident in 2008
- A description of an ACAS manoeuvre instead of the standard TCAS RA. Such a description may be lengthy, unstructured, incorrect or incomplete, and therefore the controller may request a repetition or clarification
Note that in all the above cases there is a standard alternative to the words and phrases used.
Accidents and Incidents
The following events include "Phraseology" as a contributing factor:
- B738 / AT46, Jakarta Halim Indonesia, 2016 (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.)
- GLEX/F2TH, vicinity Ibiza Spain, 2012 (On 21 September 2012, two aircraft came into conflict in Class 'A' airspace whilst under radar control at night and loss of separation was resolved by TCAS RA responses by both aircraft. Investigation found that one of the aircraft had passed a procedurally-documented clearance limit without ATC clearance or intervention and that situational awareness of its crew had been diminished by communications with the conflicting aircraft being conducted in Spanish rather than English. A Safety Recommendation on resolving the "persistent problem" of such language issues was made, noting that a similar recommendation had been made 11 years earlier.)
- 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 / F50, Adelaide Australia, 2016 (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.)
- E190 / A320, Toronto ON Canada, 2016 (On 30 January 2016, an Embraer 190-100 crew lined up on their assigned departure runway in good visibility at night without clearance to do so just as an Airbus A320 was about to land on it. The Investigation attributed the incursion to crew error arising from misinterpretation by both pilots of a non-standard Ground Controller instruction to position alongside another aircraft also awaiting departure at the hold when routinely transferring them to Tower as an instruction to line up on the runway. The failure to use the available stop bar system as a basis for controller incursion alerting was identified.)
- ALLCLEAR? Toolkit
- SAY AGAIN phraseology guide
- Communication Guide for General Aviation VFR Flights
- Safety Reminder Message, 20090421, Missed Approach RTF Communications
- CAP 413 Radiotelephony Manual, UK CAA, 23rd edition, effective 17 August 2020
- CAP 413 Radiotelephony Manual, UK CAA, 22nd edition, valid until 17 August 2020
- EU Regulation 2016/1185
AGC Safety Letters:
EUROCONTROL Action Plan for Air-Ground Communications Safety: