ICAO English Level 4, known as Operational Level 4, is the minimum operational proficiency level under ICAO's language proficiency requirements. For an air traffic controller, the practical question is whether you can understand work-related information, make your meaning clear, and keep communicating when something unexpected happens. Native-like pronunciation is not the goal, and memorising standard phraseology does not demonstrate the full range of skills involved. See ICAO's licensing FAQ and Doc 9835.

If you are preparing for an assessment, understanding the standard helps you decide what to practise. If you already work as a controller, it offers a useful question to ask yourself: when a familiar exchange turns into an unexpected explanation or follow-up question, can you still get your meaning across?

Language proficiency and operational competence

ICAO's framework concerns the language used in radiotelephony communications. This article focuses on English. A language rating alone does not establish that someone is qualified to perform all the duties of an air traffic controller. Licensing, operational qualifications and recognition of test results remain matters for the relevant authority.

Doc 9835, paragraph 4.5.5, explains that the scale assesses speaking and listening in an aviation work context, including voice-only communication. It does not assess reading and writing. Reading manuals is valuable, but preparation also needs to involve speaking and responding to what you hear.

What Level 4 means across the six skills

The following is a brief explanation of the six areas, rather than a reproduction of the full descriptors. Read the complete wording in the ICAO Personnel Licensing FAQ, under “Guidance on the evaluation of language proficiency.”

  • Pronunciation: An accent is acceptable; its effect on intelligibility matters. Pronunciation features should only occasionally make understanding harder.
  • Structure: Basic grammar is generally controlled. Errors, including under unexpected conditions, should seldom obscure meaning.
  • Vocabulary: You generally have enough language for familiar, concrete work topics and can often explain around a missing word.
  • Fluency: Speech proceeds at a suitable pace. Moving beyond rehearsed language may cause hesitation without derailing communication.
  • Comprehension: Understanding is generally accurate for familiar work topics and intelligible accents. Complications may require clarification or extra processing time.
  • Interactions: Replies are generally prompt, relevant and useful. You sustain exchanges through surprises and resolve misunderstandings.

Words such as “generally” and “occasionally” matter. Level 4 allows some imperfection. A momentary search for a word followed by a clear explanation is a different performance from being unable to explain the problem at all.

Your lowest skill rating determines the overall result

Doc 9835, paragraph 4.5.5, states that the overall rating is the lowest of the six individual ratings, not their average.

For example, suppose the six ratings are 5, 4, 4, 4, 3 and 4. The overall result is Level 3. This is a hypothetical example to illustrate the method, not an actual candidate's result.

That has a practical consequence for study time. If comprehension is your main difficulty, saying familiar instructions faster may do little to address it. A more useful exercise would be to listen to an unfamiliar explanation, identify what you have understood, and state what still needs clarification.

Standard phraseology is part of the picture

Use standard phraseology where it is specified. When it cannot convey the intended message, plain language is needed. ICAO Circular 323, section 3.8.3, explains that relationship; sections 1.1.2–1.1.4 discuss communication practice and coverage of all six skills.

A trainee may handle familiar level and heading exchanges confidently, yet struggle when a crew explains that it cannot continue climbing while it checks a problem. The language task now includes understanding an explanation, noticing an information gap and asking a relevant question. Rehearsed expressions provide a foundation, but learners also need opportunities to respond without a script.

What clarification looks like in a short exchange

The following passage is an original ATCBase language-learning example. Callsigns and the full procedural context are omitted; it is not an operational phraseology template.

Pilot: We cannot continue the climb at the moment. We are checking a problem.

Controller: Do you mean you need to stop climbing now?

Pilot: Yes. We need a few minutes to complete the checks.

Notice what the controller's question does. It makes an interpretation explicit and gives the pilot a chance to confirm it. The reply then adds information about the time needed. Both speakers contribute to a shared understanding.

A vague “OK” would leave it unclear exactly what had been understood. Checking a particular meaning can expose a misunderstanding while there is still an opportunity to correct it. Doc 9835, section 4.6.7, discusses checking, confirmation and clarification as aspects of interaction.

These three sentences cannot establish a speaker's ICAO level. Written dialogue does not reveal pronunciation, listening performance, hesitation or response time. A formal rating needs sufficient evidence of the person's language performance.

Turn the standard into a practice task

Our suggestion is to start with a familiar work-related topic, such as a weather deviation or a technical problem reported by a crew. Listen to a short account without reading a transcript. Explain what you understood and identify anything you would need to clarify.

Next, ask a practice partner to rephrase the situation and add a question you have not prepared for. Use the vocabulary you have. If a word will not come to mind, try describing the function, condition or effect you mean. Your partner should be able to follow the explanation.

Listen back to the recording and choose one specific improvement. Was a sentence ambiguous? Did you answer the question that was actually asked? Did a pause make the exchange difficult to continue? Repeat the task with that point in mind. This is a way to organise practice, not a substitute for a formal assessment.

You can use the same approach when reviewing an ATCBase training session: choose one explanation or clarification and check whether your response addressed what the other speaker said. ATCBase practice and feedback support learning; they do not constitute an authority-recognised language proficiency examination.

Check the reassessment rules that apply to you

The ICAO FAQ explains that proficiency below Level 6 requires periodic formal reassessment. Authorities set the intervals; ICAO recommends three years for Level 4 and six for Level 5. Check your authority's current requirements when planning a test or reassessment.

For your next practice session, set a concrete goal: when the other speaker rephrases something or adds an unexpected detail, can you follow it, explain your understanding and clarify what remains uncertain? That gives you a useful way to identify what to work on next.

Sources and further reading

Last reviewed: September 30, 2026. This is an independent ATCBase explanation. The dialogue and practice suggestions are our own. Refer to the source documents for the official wording and to your licensing authority for applicable national requirements.