ATC Phraseology
Standard radiotelephony phraseology for pilots — aligned with ICAO Annex 10 and UK CAA CAP 413.
Standard phraseology exists to reduce misunderstandings in radio communications. Pilots must read back specific elements of clearances to confirm receipt. When standard phraseology does not cover a situation, plain language may be used — but always be clear, concise, and unambiguous.
Read-Back Requirements
The following items MUST be read back in full when received from ATC: ATC route clearances, clearances and instructions to enter, land on, take off from, hold short of, cross, or taxi on any runway, runway-in-use information, altimeter settings, SSR codes (squawk), level instructions, heading and speed instructions, transition levels.
General Calling Procedure
Standard call structure: WHO YOU ARE CALLING + WHO YOU ARE + YOUR POSITION/LEVEL + WHAT YOU WANT. Always establish two-way communications before transmitting a full message on first contact with a new unit.
Pre-Flight / Clearance Delivery
| Situation | Pilot Says | ATC Responds |
|---|---|---|
| Request IFR clearance | "[callsign], request clearance to [destination], [aircraft type], [departure time]" | "[callsign], cleared to [dest], [route], climb [level], squawk [code]" |
| Read back clearance | "[Read back full clearance], [callsign]" | "Readback correct" or "Negative, [correction]" |
| Request start-up | "[callsign], request start-up" | "[callsign] start-up approved" or "not yet available, expect [time]" |
| Request ATIS | "[callsign], request ATIS information" | "ATIS information [letter], [time], [conditions summary]" |
| Confirm ATIS received | "[callsign], information [letter]" | "[callsign] roger" |
Ground Movement (Taxi)
| Situation | Example Exchange |
|---|---|
| Request taxi | "Speedbird 123, request taxi, information Charlie." ATC: "Speedbird 123, taxi to holding point Runway 27L via Alpha, Bravo." |
| Read-back (mandatory) | "Taxi holding point Runway 27L via Alpha, Bravo, Speedbird 123." Runway and hold-short instructions must always be read back. |
| Hold position | ATC: "Speedbird 123, hold position." Pilot: "Holding, Speedbird 123." |
| Crossing runway | ATC: "Speedbird 123, cross Runway 09." Pilot: "Cross Runway 09, Speedbird 123." |
| Line-up instruction | ATC: "Speedbird 123, line up Runway 27L." Pilot: "Lining up Runway 27L, Speedbird 123." |
Take-Off
| Situation | ATC | Pilot |
|---|---|---|
| Conditional line-up clearance | "Speedbird 123, behind the landing Boeing 737, line up Runway 27L" | "Behind the Boeing 737, lining up Runway 27L, Speedbird 123" |
| Take-off clearance | "Speedbird 123, wind 270 degrees 12 knots, cleared take-off Runway 27L" | "Cleared take-off Runway 27L, Speedbird 123" |
| Take-off abandoned | "Speedbird 123, stop immediately, stop immediately" | "Stopping, Speedbird 123" — declare MAYDAY and squawk 7700 if emergency |
Departure / En-Route
| Situation | Example Call |
|---|---|
| Initial contact after take-off | "[callsign], airborne [time], passing [level], climbing [cleared level]" |
| Level report | "[callsign], maintaining Flight Level [XXX]" |
| Requesting higher level | "[callsign], request Flight Level [XXX]" |
| Reporting position | "[callsign], [position], [level], estimating [next position] at [time]" |
| Requesting direct routing | "[callsign], request direct [waypoint]" |
| Frequency change | ATC: "Contact [unit] [frequency], [callsign]" Pilot: "Contact [unit] [frequency], [callsign]" — read-back required |
Annotated VFR Departure, Start to Handover
The tables above give you the words. This section gives you the reasoning. Below is a complete VFR departure from Gloucester, a UK aerodrome with an ATZ in Class G airspace, in a PA-28 registered G-BXKL, with a plain-English note after each transmission explaining why it is built the way it is and what the correct response actually commits you to.
Why this shape. Station called, then who you are, then where you are, then what you want. Quoting the ATIS letter and the QNH from it tells the controller you already hold the current information, which saves a whole transmission on a busy frequency. The registration is given in full because no controller has abbreviated it yet.
Verbatim, not "roger". Three separate mandatory read-back items are stacked into one instruction: the taxi routing, the runway in use, and the altimeter setting. All three come back word for word. Note also that the controller has now abbreviated the callsign to Golf Kilo Lima, which is what permits you to do the same.
The conditional clearance. The format is fixed: callsign, the condition, the instruction, then the condition again. Saying "behind" at both ends is deliberate, so that a clipped transmission cannot leave you with a bare "line up runway two seven". The condition has to refer to one aircraft that you can see and identify, and you stay where you are until it has passed in front of you. In the UK a conditional clearance involving the runway in use is only issued when both controller and pilot can see the aircraft concerned.
What comes back and what does not. The clearance and the runway are read back. The surface wind is information, so it is not repeated; adding it just lengthens the transmission. This is also the only point in the entire flight at which the word "take-off" is used, for reasons covered in the next section.
Wilco versus roger versus read-back. The level restriction is a level instruction, so it is read back. "Report leaving the ATZ" asks for a future action rather than issuing a clearance, so it is acknowledged with wilco (will comply). Roger would only confirm you heard it and commits you to nothing, which is why roger is the wrong answer to anything that asks you to do something. Note the time is given as minutes only: "five three", not "one four five three".
Two read-back items and one warning. SSR codes and frequency instructions are both on the UK mandatory read-back list in CAP 413. "Freecall" is the word that matters here: it means no coordination has taken place and Brize is not expecting you. Compare with "contact", which implies the next unit has been told about you. A freecall to a busy LARS unit can be refused.
Abbreviation resets. New unit, full registration again. Brize has not abbreviated your callsign and has no idea whether another Golf Kilo Lima is already on frequency. The same applies on a go-around or after any change of controlling agency.
The distinction to hold on to: anything that changes where the aircraft is allowed to be (runway, route, level, heading, speed, squawk, frequency, altimeter setting) is read back in the controller's own words. Anything that is information (wind, traffic, weather) or a request for a future report is acknowledged with roger or wilco. If you find yourself reading back the surface wind, you are padding; if you find yourself saying "roger" to a level, you are making a mistake that has caused level busts.
Why the Phraseology Is Shaped This Way
Standard phraseology looks arbitrary until you know which accident produced each rule. Most of the wording in CAP 413 was written after something went wrong.
The word "take-off" and Tenerife, 1977
On 27 March 1977 two Boeing 747s collided on the runway at Los Rodeos, Tenerife, killing 583 people. The KLM crew, waiting at the end of a fog-bound runway, transmitted "we are now at take-off" while beginning the roll. The controller, taking it as a statement of position, replied "OK, stand by for take-off, I will call you". The second half of that reply was blocked by a simultaneous transmission from the Pan Am crew reporting that they were still backtracking on the same runway. Both aircraft heard a squeal instead of the words that would have prevented the accident.
Three rules came out of it, and they are the reason the exchange above reads the way it does:
- The word "take-off" appears only in the clearance itself and in its cancellation. At every other point, including position reports and requests, the word is "departure". "Ready for departure", never "ready for take-off".
- "Cleared for take-off" is read back in full, so the controller hears confirmation that the clearance reached the correct aircraft.
- Conditional clearances carry the condition twice and are never used to imply a take-off clearance.
The blocked transmission problem has not gone away. Two aircraft transmitting at once on the same VHF frequency produce a heterodyne squeal or, worse, one clear transmission with the other completely masked. If a read-back sounds wrong, sounds like it came from the wrong aircraft, or you hear a carrier without words, ask. "Confirm cleared for take-off, Golf Kilo Lima" costs three seconds.
"Line up and wait" replacing "position and hold"
US controllers said "taxi into position and hold" until 30 September 2010, when the FAA adopted the ICAO phrase "line up and wait". The old wording had two problems. It contained the word "hold", which in every other context means stop and do not proceed, sitting in an instruction that told you to move onto an active runway. And it named no runway, so a crew at an intersection with two runways in front of them had nothing in the clearance to check against. "Line up and wait runway two seven" identifies the surface you are entering and separates the movement from the waiting.
The missing word "to"
Level instructions omit the word "to" before the figure: "climb altitude two thousand four hundred feet", not "climb to two thousand four hundred feet". Spoken quickly, "to two" and "two two" are the same sound, and levels have been misread as a result. The same instinct removed "yes" (replaced by "affirm", because "affirmative" and "negative" share their ending) and removed "repeat" in favour of "say again", since "repeat" is a live artillery command in joint civil and military operations.
Why the callsign moves
On a request the callsign goes first, because the controller needs to know who is speaking before deciding whether to listen. On a read-back it goes last, because by then the controller is checking the content and needs the identity as the final confirmation of whose read-back was correct. Getting this backwards is harmless in itself, but it is the clearest single marker of an inexperienced voice on frequency.
Approach & Landing
| Situation | ATC | Pilot |
|---|---|---|
| Descent for approach | "[callsign] descend to [level], expect ILS Runway 27L" | "Descend [level], expect ILS Runway 27L, [callsign]" |
| Speed control | "[callsign] reduce speed to 180 knots" | "Reducing to 180 knots, [callsign]" |
| ILS approach clearance | "[callsign] cleared ILS approach Runway 27L" | "Cleared ILS approach Runway 27L, [callsign]" |
| Landing clearance | "[callsign] wind 270/10, cleared to land Runway 27L" | "Cleared to land Runway 27L, [callsign]" |
| Go-around | "[callsign] go around" | "Going around, [callsign]" — execute published missed approach immediately |
Common Standard Phrases
| Phrase | Meaning |
|---|---|
Roger | I have received all of your last transmission |
Wilco | I understand and will comply (implies "Roger" — do not say "Roger Wilco") |
Affirm | Yes (never use "affirmative" or "yes") |
Negative | No / that is not correct |
Say again | Repeat your last transmission (never use "repeat" — reserved for artillery) |
Stand by | Wait — I will call you (no reply required; not a clearance to act) |
Confirm | Have I correctly received the following… / Is that correct? |
Correct | That is correct |
Approved | Permission granted for the proposed action |
Unable | Cannot comply with the instruction or request |
Words twice | Communication difficult — transmit each phrase twice |
Check | Examine a system or procedure (no reply expected) |
Transponder / Squawk Instructions
| Instruction from ATC | Pilot Action & Read-Back |
|---|---|
| "Squawk [code]" | Set transponder to given 4-digit code. Read back: "Squawk [code], [callsign]" |
| "Squawk IDENT" | Press the IDENT button once. Read back: "Ident, [callsign]" |
| "Squawk standby" | Select transponder standby mode (no reply is transmitted) |
| "Squawk Charlie" | Select Mode C — enable altitude reporting |
| "Stop squawk Charlie" | Turn off Mode C altitude reporting |
Distress and Urgency
MAYDAY MAYDAY MAYDAY — Distress call. Transmit the word three times before the message. Indicates grave and imminent danger requiring immediate assistance. Squawk 7700.
PAN PAN PAN PAN PAN PAN — Urgency call. Transmit three times before the message. Indicates an urgent situation not requiring immediate assistance but needing priority handling.
See Emergency Procedures for full guidance on distress calls, emergency squawk codes, and lost communications procedures.
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