RTR(A) phraseology

Core RT rules

Radio checks, callsigns and numbers, read-back rules, and the phrases that keep a frequency workable.

Affirm, Negative, Roger, Wilco

The four single-word acknowledgements used to keep RT exchanges short and unambiguous. AFFIRM means yes; NEGATIVE means no; ROGER means "I have received your last transmission" but does NOT imply compliance; WILCO combines understanding with intent to comply.

Pilot

AFFIRM / NEGATIVE / ROGER / WILCO, [Callsign]

ATC

[Callsign] [confirmation or further instruction]

ATC

Akasa Air 1532, confirm FL320

Pilot

Affirm, FL320, Akasa Air 1532

ATC

Akasa Air 1532, expect descent in five minutes

Pilot

Wilco, Akasa Air 1532

ICAO Doc 9432 specifies AFFIRM, not "affirmative", "affirmative" is non-standard despite common informal usage.
ROGER alone is never enough for read-back items. A verbatim read-back is required for level, heading, frequency, runway, squawk, taxi, hold-short and QNH.
WILCO already includes ROGER, never say "roger wilco".

Reference: ICAO Doc 9432 §2.6

Cancel IFR Flight / Change to VFR

Used in flight when the pilot can continue VMC and wants to release the IFR clearance, freeing controller workload and removing IFR airspace restrictions.

Pilot

[Station] [Callsign] CANCELLING IFR, CONTINUING VFR

ATC

[Callsign] IFR CANCELLED AT [time], SQUAWK [VFR conspicuity code 7000]

Pilot

Delhi Approach, Akasa Air 1532, cancelling IFR, continuing VFR

ATC

Akasa Air 1532, Delhi Approach, IFR cancelled at 43, squawk 7000, frequency change approved

Pilot

IFR cancelled 43, squawk 7000, frequency change approved, Akasa Air 1532

Cancelling IFR is a statement, not a request. ATC will accept it and assign the appropriate VFR squawk code.
You cannot re-enter IFR by simply asking, you'd need a fresh IFR clearance.

Reference: ICAO Doc 9432

File Airborne Flight Plan

Used in flight to file a flight plan that was not filed before departure, common when a VFR flight decides to extend cross-country or when an aircraft diverts to an unplanned destination. The relevant FIS or FIC station accepts the plan over the radio.

Pilot

[Station] [Callsign] REQUEST FILE AIRBORNE FLIGHT PLAN

ATC

[Callsign] PASS YOUR DETAILS

Pilot

Delhi Information, Akasa Air 1532, request file airborne flight plan

ATC

Akasa Air 1532, Delhi Information, pass your details

Pilot

Delhi Information, Akasa Air 1532 Delhi to Jaipur via Rohtak, FL055, endurance 4 hours, 3 persons on board, departed Delhi at 1015

ATC

Akasa Air 1532, Delhi Information flight plan filed, time 0842

Have all 19 ICAO flight plan items ready before you press the PTT, call sign, type, route, level, ETD, endurance, POB, etc.
Note the time the plan is accepted; that becomes the official filing time.

Reference: ICAO Doc 9432

How Do You Read

Used during established two-way communications when the pilot suspects readability has degraded, typical triggers are a missed transmission, an unusually weak reply, or stepped-on traffic. Unlike RADIO CHECK there is no frequency stated, because contact has already been established and the channel is implicit.

Pilot

[Station] HOW DO YOU READ [Callsign]

ATC

[Callsign] READING YOU [readability 1-5]

Pilot

Mumbai Control, Akasa Air 1532, how do you read

ATC

Akasa Air 1532, reading you 5

Pilot

Reading you 5, Akasa Air 1532

Same readability 1-5 scale as RADIO CHECK, the difference is when you use which phrase, not how the reply is structured.
Do NOT include a frequency with HOW DO YOU READ. The frequency is implicit because two-way contact is already established, and stating it suggests you mean the initial-contact form (RADIO CHECK), which would be marked down in the viva.
If two consecutive HOW DO YOU READ checks return readability below 3, treat it as a comms degradation and consider transferring to the back-up frequency before the link fails entirely.

Reference: ICAO Doc 9432 §2.3 / §2.4

Numbers and callsign conventions

For every transmission containing callsigns, levels, headings, runways, frequencies or altimeter settings.

Pilot

{RECIPIENT}, {CALLSIGN}, {MESSAGE_WITH_NUMBERS}.

ATC

{CALLSIGN}, {MESSAGE_WITH_NUMBERS}.

Pilot

Delhi Ground, Skyline 345, request taxi, information Charlie, QNH one zero zero nine.

ATC

Skyline 345, taxi via Alpha to holding point runway two niner left, QNH one zero zero nine.

Pilot

Taxi via Alpha to holding point runway two niner left, QNH one zero zero nine, Skyline 345.

Transmit most numbers digit by digit: runway two seven, heading zero eight zero, squawk four two one three.
Say DECIMAL in a frequency, for example one two one decimal seven five zero.
Keep your aircraft callsign at the end of a readback and at a point where identification matters.
Use your assigned radiotelephony callsign every time. A registration may be used only where that is the assigned callsign.

Reference: ICAO Doc 9432, Chapter 2

Radio Check

Used to test the quality and readability of a radio transmission before departure, when establishing contact on a new frequency, or whenever the pilot suspects a radio malfunction. The pilot states the frequency being used so the ground station can confirm it is receiving on the correct channel.

Pilot

[Station] [Callsign] RADIO CHECK [frequency]

ATC

[Callsign] READING YOU [readability 1-5]

Pilot

Delhi Ground, Akasa Air 1532, radio check 121.9

ATC

Akasa Air 1532, Delhi Ground, reading you 5

Pilot

Reading you five, Akasa Air 1532

Readability is reported on a 1-5 scale: 1 (unreadable), 2 (readable now and then), 3 (readable but with difficulty), 4 (readable), 5 (perfectly readable).
If readability is below 3, switch to the back-up frequency or request a different channel rather than continuing on a marginal link.
Pilot read-back closes the loop, always end with your own readability assessment.
RADIO CHECK is for INITIAL contact (you state the frequency so the station can confirm tuning). Once contact is established, the established-contact variant is HOW DO YOU READ, see the next topic.

Reference: ICAO Doc 9432 §2.3

Read-Back of Clearance

Mandatory verbatim read-back of safety-critical clearances so ATC can verify the pilot has copied them correctly. Items requiring read-back are clearance limit, route, level, heading, speed, transponder code, frequency, runway in use, taxi instructions, hold-short instructions and altimeter setting.

Pilot

[full read-back of all read-back items], [Callsign]

ATC

[Callsign] [Station] [clearance] → [Callsign] READBACK CORRECT

Pilot

Delhi Delivery, Akasa Air 1532 Stand 24, request clearance Mumbai information Bravo

ATC

Akasa Air 1532, Delhi Delivery, cleared to Mumbai via direct BUBKO flight planned route, climb FL320, squawk 5271

Pilot

Cleared to Mumbai via direct BUBKO flight planned route, climb FL320, squawk 5271, Akasa Air 1532

ATC

Akasa Air 1532, readback correct

Read back the items, not a paraphrase. "Cleared as filed" is not a substitute for the level and route.
Always end the read-back with your callsign so ATC can match it to the right aircraft.
ATC includes its station name in the FIRST reply (initial contact rule, ICAO Doc 9432 §2.4.1). On subsequent transmissions on the same frequency, the station name may be omitted, note how the "readback correct" confirmation drops the "Delhi Delivery".
Acknowledgement of read-back ("readback correct") closes the loop. Do not assume your read-back was correct just because ATC went silent.

Reference: ICAO Annex 10 Vol II §5.2.1.7

Request Time Check

Requested before departure or in flight to synchronise the cockpit clock with UTC. Time is given to the nearest minute unless half-minute precision is specifically requested.

Pilot

[Station] [Callsign] REQUEST TIME CHECK

ATC

[Callsign] TIME [hours and minutes UTC]

Pilot

Delhi Ground, Akasa Air 1532, request time check

ATC

Akasa Air 1532, Delhi Ground, time 0743

Pilot

Time 0743, Akasa Air 1532

Time is always UTC, never local, and read as hours and minutes ("zero seven four three", not "seven forty-three").
If you need seconds, append "and a half" (e.g. "time zero seven four three and a half").

Reference: ICAO Doc 9432

Request Words Twice

Used during periods of poor radio quality when individual words are difficult to copy. It asks ATC to repeat each significant element twice in a single transmission, reducing the risk of mishearing.

Pilot

[Station], [Callsign], TRANSMISSION GARBLED, WORDS TWICE

ATC

[message with each significant group repeated twice]

Pilot

Delhi Approach, Akasa Air 1532, transmission garbled, words twice

ATC

Akasa Air 1532, Delhi Approach, descend descend, FL one five zero one five zero, QNH1013 1013

Request "words twice", never "say again" repeatedly, when reception is poor; it is a single solution rather than several round-trips.
When you are the one transmitting in poor conditions, you can also offer "I will say my words twice".

Reference: ICAO Doc 9432

Say Again

Used to ask ATC to repeat their last transmission, in part or in full, when something was missed, garbled, or stepped on by another transmission.

Pilot

SAY AGAIN [or SAY AGAIN ALL AFTER / ALL BEFORE / BETWEEN], [Callsign]

ATC

[acknowledgement and repetition of requested portion]

ATC

Akasa Air 1532, climb FL320, contact Mumbai Control 132.05

Pilot

Say again all after climb, Akasa Air 1532

ATC

Akasa Air 1532, all after climb: FL320, contact Mumbai Control 132.05

"Say again all after [word]" and "say again all before [word]" are precise, use them instead of asking for a full repeat when you only missed part.
"Say again" alone means repeat the entire previous transmission.
If two stations transmit simultaneously you'll hear a squeal, that's your cue to ask for a repeat.

Reference: ICAO Doc 9432

Speak Slower

Used when ATC's transmission rate is too fast to copy accurately, common with short clearances at busy hubs. It is not an admission of weak English; it is a safety request and ATC will comply without comment.

Pilot

SPEAK SLOWER, [Callsign]

ATC

[acknowledgement and slower repetition]

ATC

Akasa Air 1532, Mumbai control, cleared to Mumbai via flight planned route, climb FL350, squawk 5271

Pilot

Speak slower, Akasa Air 1532

ATC

Akasa Air 1532, Mumbai Control ... cleared to Mumbai ... via flight planned route ... climb FL350 ... squawk 5271

Always include your callsign with the request so ATC knows who is asking, at the end of the transmission, after the request itself.
It is preferable to say "speak slower" once than to read back incorrectly and force a full re-issue.

Reference: ICAO Doc 9432

Standby

Used by ATC to instruct the pilot to wait while the controller handles other traffic or sources information. "Standby" is not approval, the pilot continues with the current clearance and waits for the next call. Pilots may also use "standby" to delay a transmission they are not yet ready to make.

Pilot

STANDBY, [Callsign]

ATC

[Callsign] STANDBY

Pilot

Mumbai Control, Akasa Air 1532, request descent

ATC

Akasa Air 1532, Mumbai Control, standby

Pilot

Standby, Akasa Air 1532

"Standby" never authorises an action, do not begin the requested manoeuvre until the cleared call is received.
If standby exceeds about two minutes, prompt with "[Callsign] confirm standby", controller workload may have caused the call to slip.

Reference: ICAO Doc 9432

Unable to Comply

Used when an instruction cannot be safely or legally complied with, e.g. requested level is above the aircraft's certified ceiling, requested heading would penetrate weather, or the speed is below clean configuration speed.

Pilot

UNABLE [the instruction], [brief reason], REQUEST [alternative], [Callsign]

ATC

[Callsign] ROGER, [revised instruction]

ATC

Akasa Air 1532, Mumbai Control, climb FL410

Pilot

Unable FL410 due weight, request FL390, Akasa Air 1532

ATC

Akasa Air 1532 roger, climb FL390

"Unable" must be followed by a brief reason and, where possible, an alternative, ATC needs the picture to plan the next move.
"Unable" overrides the original instruction the moment you transmit; do not begin compliance and then call unable.

Reference: ICAO Doc 9432

What you must read back

After every safety-related clearance or instruction.

Pilot

{CALLSIGN} readback of {ROUTE_OR_INSTRUCTION}, followed by your callsign.

ATC

{CALLSIGN}, {CORRECTION_OR_READBACK_CHECK}.

ATC

Skyline 345, climb flight level two zero zero.

Pilot

Climb flight level two zero zero, Skyline 345.

ATC

Skyline 345, correction, climb flight level two five zero.

Pilot

Climb flight level two five zero, Skyline 345.

Always read back route clearances, runway entry, landing, take-off, backtrack, cross and hold-short instructions.
Also read back runway in use, altimeter settings, transponder codes, level, heading, speed and transition-level instructions.
Acknowledge other instructions so the controller knows you understood and will comply.
If any part is unclear, say SAY AGAIN or CONFIRM. Never guess a number.

Reference: ICAO Doc 9432, 2.8.3