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 Chapter 12 and in ICAO Doc 9432 - Manual of Radiotelephony and in Amendment 4 to the Acceptable Means of Compliance and Guidance Material to Regulation (EU) No 923/2012. Many national authorities also publish radiotelephony manuals which amplify ICAO provisions, and in some cases modify them to suit local conditions.
Non-standard phraseology 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.
The dedicated SID/STAR phraseology allows ATC and aircrew to communicate and understand detailed clearance information that would otherwise require long and potentially complex transmissions. Over time, these benefits have been eroded through the development of non-harmonised practices and different meanings being attached to certain elements of the SID/STAR phraseology. Consequently, a mismatch between ATC and aircrew understanding of SID/STAR phraseology presents a safety risk that requires a renewed effort to adopt and apply strictly harmonised SID/STAR phraseology.
In June 2016 ICAO published Amendment 7-A to PANS-ATM, applicable as from 10 November 2016, which includes harmonised phraseologies for issuing standard clearances to arriving and departing aircraft, including clearances to aircraft on a SID or STAR. The phraseology can be consulted in "Further Reading" below. The period over which the changes should be introduced has been notified by ICAO as 12 months commencing 10 November 2016, i.e. implementation date will vary from state to state depending on the NAA. The transition period will likely affect pilots making international IFR flights. Also, controllers from ATC Units in States which have not begun using the new procedures themselves should be aware that pilots from other States which have done so are likely to use them.
The introduction of radiotelephony (RT) phraseologies for the provision of FIS/AFIS is necessary to ensure unambiguous air–ground voice communication between air traffic services (ATS) units and pilots, thus increasing safety. It is of particular importance for cross-border flights which receive FIS/AFIS services, and should considerably reduce the possibility for misinterpretations in air–ground voice communications between ATS units and pilots.
In November 2021 EASA adopted an amendment to the Acceptable Means of Compliance (AMC) and Guidance Material (GM) to Commission Regulation (EU) No 923/2012 on Standardised European Rules of the Air (the SERA IR) introducing:
- a comprehensive set of AFIS RT phraseologies for air–ground voice communications between pilots and AFIS units;
- some additional RT phraseologies applicable to both FIS and AFIS to address specific operational situations; and
- structural amendments to clearly indicate which RT phraseologies are applicable when different ATS (air traffic control (ATC) service and/or FIS, including AFIS) are provided, thus supporting their harmonised use in a safe manner.
Failure to use standard phraseology can lead to misunderstanding, breakdown of the communication process and eventually to loss of separation.
- Adoption by National Civil Aviation Authorities of the ICAO standardised phraseology.
- Improved training in standard phraseology for pilots and ATCOs.
- Insistence by managers and aircraft commanders on the use of standard phraseology.
- Obtaining confirmation or clarification whenever doubt exists as to the content or meaning of a message.
Related Accidents and Incidents
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.
The investigation found that “Had the revised ICAO (SID R/T phraseology) procedures been adopted by the UK, it is likely that this incident would have been prevented because (the Cessna) would have leveled off at 3000 ft regardless of its cleared altitude.”
Whilst a light aircraft was lined up for departure, a vehicle made an incorrect assumption about the nature of an ambiguously-phrased ATC TWR instruction and proceeded to enter the same runway. There was no actual risk of conflict since, although LVP were still in force after earlier fog, the TWR controller was able to see the vehicle incursion and therefore withhold the imminent take off clearance.
The subsequent Investigation noted that it was imperative that clearance read backs about which there is doubt are not made speculatively in the expectation that they will elicit confirmation or correction.
AGC Safety Letters:
EUROCONTROL Action Plan for Air-Ground Communications Safety: