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|Category:||Air Ground Communication|
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:
- B763, en-route, Northern France, 1998 (On 9 January 1998, a Boeing 767-300 operated by United Airlines experienced an electrical systems malfunction subsequently attributed to arcing in a faulty electrical loom. The crew elected to divert to London Heathrow where emergency evacuation was carried out on a taxiway upon landing.)
- BN2P / B763, vicinity Kagoshima Japan, 2015 (On 10 October 2015, a Britten-Norman BN2 instructed to join final behind a Boeing 767 instead joined in front of it which obliged the 767 crew to make a go around. The Investigation was unable to establish why the BN2 pilot failed to follow their conditional clearance but noted that the 'follow' clearance given onto final approach had not been accompanied by a sequence number, and when giving the aircraft type to be followed so that its sighting could be reported, the controller had not challenged the incomplete readback or repeated the aircraft type when subsequently issuing the clearance.)
- B744 / MD90, New Chitose Japan, 2008 (On 16 February 2008, during daylight and in poor visibility, a Boeing 747-400, operated by Japan Airlines, was holding on a taxiway next to runway 01R of New Chitose Airport, Japan. A Douglas MD-90-30 operated by the same airline landed on the same runway and was still on the runway when the B747 was cleared to line up and wait. Shortly after lineup the B747 began its takeoff roll without receiving such clearance and subsequently was instructed to abort the takeoff. The crew of the B747 successfully rejected the takeoff.)
- AS32 / B734, Aberdeen UK, 2000 (For reasons that were not established, a Super Puma helicopter being air tested and in the hover at about 30 feet agl near the active runway at Aberdeen assumed that the departure clearance given by GND was a take off clearance and moved into the hover over the opposite end of the runway at the same time as a Boeing 737 was taking off. The 737 saw the helicopter ahead and made a high speed rejected take off, stopping approximately 100 metres before reaching the position of the helicopter which had by then moved off the runway still hovering.)
- 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.)
- ALLCLEAR? Toolkit
- SAY AGAIN phraseology guide
- Communication Guide for General Aviation VFR Flights
- Safety Reminder Message, 20090421, Missed Approach RTF Communications
AGC Safety Letters:
EUROCONTROL Action Plan for Air-Ground Communications Safety: