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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:
- 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.)
- 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.)
- 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.)
- A320 / B739, Yogyakarta Indonesia, 2013 (On 20 November 2013, an A320 misunderstood its taxi out clearance at Yogyakarta and began to enter the same runway on which a Boeing 737, which had a valid landing clearance but was not on TWR frequency, was about to touch down from an approach in the other direction of use. On seeing the A320, which had stopped with the nose of the aircraft protruding onto the runway, the 737 applied maximum manual braking and stopped just before reaching the A320. The Investigation faulted ATC and airport procedures as well as the A320 crew for contributing to the risk created.)
- 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.)
- 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: