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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:
- A319 / AS32, vicinity Marseille France, 2016 (On 27 June 2016, an Airbus A319 narrowly avoided a mid-air collision with an AS532 Cougar helicopter whose single transponder had failed earlier whilst conducting a local pre-delivery test flight whilst both were positioning visually as cleared to land at Marseille and after the helicopter had also temporarily disappeared from primary radar. Neither aircraft crew had detected the other prior to their tracks crossing at a similar altitude. The Investigation attributed the conflict to an inappropriate ATC response to the temporary loss of radar contact with the helicopter aggravated by inaccurate position reports and non-compliance with the aerodrome circuit altitude by the helicopter crew.)
- CRJ2, en-route, Jefferson City USA, 2004 (On October 14, 2004, a Bombardier CRJ-200 being operated by Pinnacle Airlines on a non revenue positioning flight crashed into a residential area in the vicinity of Jefferson City Memorial Airport, Missouri after the flight crew attempted to fly the aircraft beyond its performance limits and a high altitude stall, to which their response was inappropriate, then followed.)
- B773, vicinity Houston TX USA, 2014 (On 3 July 2014, a Boeing 777-300 departing Houston came within 200 feet vertically and 0.61nm laterally of another aircraft after climbing significantly above the Standard Instrument Departure Procedure (SID) stop altitude of 4,000 feet believing clearance was to FL310. The crew responded to ATC avoiding action to descend and then disregarded TCAS 'CLIMB' and subsequently LEVEL OFF RAs which followed. The Investigation found that an inadequate departure brief, inadequate monitoring by the augmented crew and poor communication with ATC had preceded the SID non-compliance and that the crew should have followed the TCAS RAs issued.)
- A319 / A320, Paris CDG France, 2014 (On 25 November 2014, the crew of an Airbus A320 taking off from Paris CDG and in the vicinity of V1 saw an A319 crossing the runway ahead of them and determined that the safest conflict resolution was to continue the takeoff. The A320 subsequently overflew the A319 as it passed an estimated 100 feet agl. The Investigation concluded that use of inappropriate phraseology by the TWR controller when issuing an instruction to the A319 crew had led to a breach of the intended clearance limit. It was also noted that an automated conflict alert had activated too late to intervene.)
- B734, Sharjah UAE, 2015 (On 24 September 2015, a Boeing 737-400 cleared for a night take-off from Sharjah took off from the parallel taxiway. The controller decided that since the taxiway was sterile and the aircraft speed was unknown, the safest option was to allow the take-off to continue. The Investigation noted that the taxiway used had until a year previously been the runway, becoming a parallel taxiway only when a new runway had been opened alongside it. It was noted that the controller had "lost visual watch" on the aircraft and regained it only once the aircraft was already at speed.)
- 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: