ICAO (The International Civil Aviation Organisation) demands that ..... all airline and helicopter pilots who fly internationally, and all air traffic controllers who provide services to international flights..... .....  must have a minimum level of English. This level of English is known as ICAO Operational Level 4. ICAO has developed a rating scale with Level 4 considered the minimum acceptable level (’Operational Level’)


Pronunciation:     (Assumes a dialect and/or accent intelligible to the aeronautical community) Pronunciation, stress, rhythm, and intonation are influenced by the first language or regional variation but only sometimes interfere with ease of understanding. Pronunciation, stress, rhythm, and intonation are influenced by the first language or regional variation but only sometimes interfere with ease of understanding.  Structure: (Relevant grammatical structures and sentence patterns are determined by language functions appropriate to the task)   Basic grammatical structures and sentence patterns are used creatively and are usually well controlled. Errors may occur, particularly in unusual or unexpected circumstances, but rarely interfere with meaning. Vocabulary: Vocabulary range and accuracy are usually sufficient to communicate effectively on common, concrete, and work- related topics. Can often paraphrase successfully when lacking vocabulary in unusual or unexpected circumstances. Fluency: Produces stretches of language at an appropriate tempo. There may be occasional loss of fluency on transition from rehearsed or formulaic speech to spontaneous interaction, but this does not prevent effective communication. Can make limited use of discourse markers or connectors. Fillers are not distracting. Comprehension:  Comprehension is mostly accurate on common, concrete, and work-related topics when the accent or variety used is sufficiently intelligible for an international community of users. When the speaker is confronted with a linguistic or situational complication or an unexpected turn of events, comprehension may be slower or require clarification strategies. Interactions: Responses are usually immediate, appropriate, and informative. Initiates and maintains exchanges even when dealing with an unexpected turn of events. Deals adequately with apparent misunderstandings by checking, confirming, or clarifying.
ICAO has developed the following “Holistic Descriptors”. Proficient speakers shall: communicate effectively in voice-only (telephone/radiotelephone) and in face-to-face situations communicate on common, concrete and work-related topics with accuracy and clarity use appropriate communicative strategies to exchange messages and to recognize and resolve misunderstandings (e.g. to check, confirm, or clarify information) in a general or work-related context handle successfully and with relative ease the linguistic challenges presented by a complication or unexpected turn of events that occurs within the context of a routine work situation or communicative task with which they are otherwise familiar use a dialect or accent which is intelligible to the aeronautical community The full ICAO language proficiency descriptors can be found here.