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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:
- A320, vicinity Lyons Saint-Exupéry France, 2012 (On 11 April 2012, a Hermes Airlines A320 commanded by a Training Captain who was also in charge of Air Operations for the airline was supervising a trainee Captain on a night passenger flight. The aircraft failed to establish on the Lyons ILS and, in IMC, descended sufficiently to activate both MSAW and EGPWS 'PULL UP' warnings which eventually prompted recovery. The Investigation concluded that application of both normal and emergency procedures had been inadequate and had led to highly degraded situational awareness for both pilots. The context for this was assessed as poor operational management at the airline.)
- 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.)
- C525 / B773, vicinity London City UK, 2009 (On 27 July 2009, a Cessna 525 departing from London City failed to comply with the initial 3000 ft QNH SID Stop altitude and at 4000 ft QNH in day VMC came into close proximity on an almost reciprocal heading with a Boeing 777-300ER. Actual minimum separation was approximately 0.5nm laterally and estimated at between 100 ft and 200 ft vertically.)
- A139 / A30B, Ottawa Canada, 2014 (On 5 June 2014, an AW139 about to depart from its Ottawa home base on a positioning flight exceeded its clearance limit and began to hover taxi towards the main runway as an A300 was about to touch down on it. The TWR controller immediately instructed the helicopter to stop which it did, just clear of the runway. The A300 reached taxi speed just prior to the intersection. The Investigation attributed the error to a combination of distraction and expectancy and noted that the AW139 pilot had not checked actual or imminent runway occupancy prior to passing his clearance limit.)
- A343, Changi Singapore, 2007 (On 30 May 2007, at about 0555 hours local time, the crew of an Airbus A340-300 had to apply (Take-off Go Around) power and rotate abruptly at a high rate to become airborne while taking off from Runway 20C at Singapore Changi Airport, when they noticed the centreline lights were indicating the impending end of the available runway. The crew had calculated the take-off performance based on the full TORA (Take-off Run Available) of 4,000 m because they were unaware of the temporary shortening of Runway 20C to 2,500 m due to resurfacing works.)
- 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: