Declaring an emergency would be one of the most critical conversations, however it would be limited to something like this:
Pilot: MAYDAY, MAYDAY, MAYDAY, Metro Control, Big Jet 345, main electric failure, request immediate landing at Metro, position 35 miles north
west of Metro, heading 120 flight level 80 descending, 150 persons on board, endurance three hours. ATC: Big Jet 345, Roger the MAYDAY, turn left heading 090, radar vectors ILS runway 27. Pilot: Big Jet 345 request runway 09. ATC: Big Jet 345, roger, turn right heading 140 for radar vectoring runway 09, descend to 3000 feet, QNH 995, report established. Pilot: Big Jet 345, heading 140, descend to 3000 feet QNH 995, report established localiser runway 09.
The vocabulary and the grammar used are very simple and the exchange takes advantage of the prescribed phraseology.
ICAO Chicago Convention, Annex 10. recommends using English and the local language. For both languages, local dialects are accepted as the norm. So for English there is indeed no reference to British or American, or any other variation.
Since 2003, ICAO recommends to member States to check for languages proficiency, setting the minimum acceptable level to 4. Actual and detailed requirements are found in Appendix 1 of Annex 1.
Annex 1, Appendix 1
Describes two types of criteria used to evaluate proficiency: An overall understanding, and explicit details.
- To meet the language proficiency requirements contained in Chapter 1, Section 1.2.9, an applicant for a licence or a licence holder shall
demonstrate, in a manner acceptable to the Licensing Authority,
compliance with the holistic descriptors at Section 2 and with the
ICAO Operational Level (Level 4) of the ICAO Language Proficiency
Rating Scale in Attachment A.
Overall criteria allows for different dialects and accents:
- 2. Holistic descriptors. Proficient speakers shall: [...] e) use a dialect or accent which is intelligible to the aeronautical
Detailed scale is found in Attachment A, ICAO language proficiency rating scale. I show here only levels 4 to 6, as 4 is the minimum expected for operational personnel.
1.1 Expert, extended and operational levels
ICAO member States have agreed on a set of standard phrases that must be used instead of plain language, plain language is used only when this phraseology is not effective. There is no requirement, for crew and controllers, to study the language like an interpreter would do, they just need to be understandable.
To understand the type of conversation used in regular communications:
Chicago Convention is used at national level by member States. When recommendations are not exactly followed, this is mentioned in the local AIP, section GEN 1.7 Differences from ICAO Standards, Recommended Practices and Procedures. AIPs links can be found on this Wikipedia page.
The next paragraphs just provide the references in ICAO documentation. You may skip them if not interested.
ICAO documents can be downloaded from the the Switzerland Federal Office of Civil Aviation, on this page (in French).
Standardized phraseology must be used before plain language.
- 18.104.22.168 ICAO standardized phraseology shall be used in all situations
for which it has been specified. Only when standardized
phraseology cannot serve an intended transmission, plain language
shall be used. [...] Detailed language proficiency requirements appear
in the Appendix to Annex 1.
Samples of ICAO standard phraseology found in Annex 10 (standard phrases are uppercase):
- 22.214.171.124.8 The following words and phrases shall be used in radiotelephony communications as appropriate and shall have the
meaning ascribed hereunder: [...]
- CONFIRM • “I request verification
of: (clearance, instruction, action, information).”
- CONTACT • “Establish communications with...”
- CORRECT • “True” or “Accurate”.
- CORRECTION • “An error has been made in this transmission (or
message indicated). The correct version is...”
- DISREGARD • “Ignore.”
- HOW DO YOU READ • “What is the readability of my
- I SAY AGAIN • “I repeat for clarity or emphasis.”
- MAINTAIN • “Continue in accordance with the condition(s) specified”
or in its literal sense, e.g. “Maintain VFR”.
- NEGATIVE • “No” or
“Permission not granted” or “That is not correct” or “Not capable”.
For the crews, two languages are available.
126.96.36.199.1 The air-ground radiotelephony communications shall be conducted in the language normally used by the station on the ground
or in the English language.
188.8.131.52.2 The English language shall be available, on request from any
aircraft station, at all stations on the ground serving designated
airports and routes used by international air services.
Pronunciation differences are taken into account, and there is a standardized pronunciation to be used for critical elements, like when spelling words and numbers, including when using English.
184.108.40.206 Word spelling in radiotelephony. [...] The pronunciation of the words in the alphabet as well as numbers may vary according to the
language habits of the speakers. In order to eliminate wide variations
in pronunciation, posters illustrating the desired pronunciation are
available from ICAO.
220.127.116.11.3.1 When the language used for communication is English, numbers shall be transmitted using the following pronunciation [...]
In 2003 ICAO adjusted its Annex 1 to the Chicago Convention to add language proficiency requirements:
Amendment of definitions; new provisions requiring language
proficiency for aeroplane and helicopter pilots, navigators using
radiotelephony, air traffic controllers and aeronautical station
operators; introduction of a Note on qualification and training for
aeronautical meteorology personnel; amendment to the Human Factors
knowledge requirements for Aircraft Maintenance Engineer.
This includes a requirement to demonstrate language proficiency, both for crews...
- 18.104.22.168 Aeroplane, airship, helicopter and powered-lift pilots and those flight navigators who are required to use the radio telephone
aboard an aircraft shall demonstrate the ability to speak and
understand the language used for radiotelephony communications.
and for ATCO.
- 22.214.171.124 Air traffic controllers and aeronautical station operators shall demonstrate the ability to speak and understand the language
used for radiotelephony communications.
This proficiency has to be evaluated against a common scale.
- 126.96.36.199 As of 5 March 2008, aeroplane, airship, helicopter and powered-lift pilots, air traffic controllers and aeronautical station
operators shall demonstrate the ability to speak and understand the
language used for radiotelephony communications to the level specified
in the language proficiency requirements in Appendix 1.
Those that don't match the highest level will be checked again and again...
- 188.8.131.52 Recommendation.— The language proficiency of aeroplane, airship, helicopter and powered-lift pilots, flight navigators
required to use the radiotelephone aboard an aircraft, air traffic
controllers and aeronautical station operators who demonstrate
proficiency below the Expert Level (Level 6) should be formally
evaluated at intervals.
But the natives and assimilated won't be bothered. They just need to show they are understandable by the international aeronautical community.
- Formal evaluation is not required for applicants who demonstrate expert language proficiency, e.g. native and very proficient
non-native speakers with a dialect or accent intelligible to the
international aeronautical community.