There are many factors involved in the communication process. Of all the factors, the most important may be Phraseology as it equips us to communicate rapidly, with desired results, and reduces circumstances for misunderstanding, all without being affected by differences in language.
As indicated in SKYbrary, 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.
ICAO Annex 10 Volume II Chapter 5 and in ICAO Doc 9432 - Manual of Radiotelephony outlines the International standards of phraseology. Many national authorities also publish Radiotelephony manuals which expand ICAO provisions and, in some cases, are altered to address local conditions.
Non-standard phraseology, which is sometimes used by air traffic services in an attempt to reduce problems, can contribute to misunderstandings. A balance is always sought to reduce confusion and uphold the safety of flight.
Non-standard phraseology in Europe: The UK Civil Aviation Authority (CAA) has adopted certain non-standard phraseology designed to reduce the chance of mishearing or misunderstanding radio communications. Although not in accordance with ICAO, the phraseology is based on careful research of the breakdown of pilot/controller communications. Other European countries have adopted similar non-standard phraseology as well.
The following paragraphs taken from the UK Manual of Radiotelephony summarize 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 radio exchange will also include the appropriate QFE or QNH.
- When transmitting messages containing flight levels, each digit shall be transmitted separately. However, in an endeavor to reduce altitude/level deviations 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."