12.1 Phonetic Alphabet, Phraseology and CTAF

ICAO Phonetic Alphabet and Numbers

When you transmit on an aeronautical Very High Frequency (VHF) radio, every letter and number must be unambiguous over a noisy link. The International Civil Aviation Organization (ICAO) phonetic alphabet assigns a fixed word to each letter of the English alphabet so that callsigns, waypoints and registrations survive interference and accents.

Remote pilots should learn the full set verbatim — you will hear it on every Common Traffic Advisory Frequency (CTAF) broadcast and read it back when confirming a clearance or callsign.

Numbers are spoken as single digits except where noted, with three pronunciation traps that catch new operators:

• 3 is spoken "Tree" (not "three") — the "th" sound is hard to distinguish on VHF.
• 5 is spoken "Fife" (not "five") — the trailing "v" is dropped.
• 9 is spoken "Niner" — the most important trap, because the English word "nine" can be confused with the German word "nein" (meaning "no") and with "five" on a poor link. Exam questions on this are common.

Whole hundreds are spoken as "Hundred" and thousands as "Thousand" (for example, altitude "Two Thousand Five Hundred"). The decimal point is spoken "Decimal" — used for frequencies such as "One Two One Decimal Five" for 121.5 MHz.

Standard Phraseology

Aviation radio uses a small, fixed vocabulary so that meaning does not depend on tone, idiom or fluency in English. Master these words before you key the microphone:

• Roger — "I have received and understood your last transmission." It does not mean "yes" or "I will comply."
• Wilco — "Will comply." Use it when you accept an instruction you will carry out.
• Say again — "Repeat your last transmission." Never use "repeat" — in military contexts "repeat" can mean "fire again."
• Stand by — "Wait, I will call you back." It is not a refusal, just a pause.
• Affirm / Negative — Yes / No. "Affirmative" is discouraged because it can be confused with "negative" on a poor link.
• Confirm — "I am checking — is this what you said or intend?"
• Over — "My transmission is ended and I expect a reply."
• Out — "My transmission is ended and I expect no reply." Never combine as "over and out" — they contradict each other.

Standard Call Format

Every routine call follows the same four-part shape so the called station knows who is being asked and who is asking:

1. Called station first — for example, "Brisbane Tower."
2. Calling station second — for example, "Remote Pilot Alpha Bravo Charlie Delta."
3. Message — position, intention or request.
4. "Over" if you expect a reply, or "Out" if you do not.

Putting the called station first lets the receiver know the call is for them before they hear a stranger's callsign.

Read-Back of Safety-Critical Instructions

Controllers and other pilots expect you to read back any safety-critical instruction so they can catch a misunderstanding before it becomes an incident. For a remote pilot, the items that must be read back include:

• ATC clearances (for example, "cleared to enter controlled airspace")
• Runway instructions (cleared to land, take-off, cross, backtrack)
• QNH altimeter settings
• Taxi instructions
• Squawk codes (transponder codes)
• Frequency changes

A read-back is not a parrot echo — it is a confirmation. If the read-back does not match what was said, the controller will correct you with "Negative, I said…"

CTAF at Non-Controlled Aerodromes

The Common Traffic Advisory Frequency (CTAF) is the VHF frequency used at non-controlled (Class G) aerodromes for pilots to self-sequence their traffic. There is no tower controller issuing instructions; instead, each pilot broadcasts position and intent so everyone can build a mental traffic picture and deconflict.

For a Remote Pilot Aircraft (RPA) operator, the rules are:

• Monitor the CTAF whenever you are operating within the vicinity of a non-controlled aerodrome (generally within about 5 NM and below the circuit height), even if you do not intend to transmit.
• Broadcast on CTAF when your operation could affect other traffic — for example launching or recovering near the circuit, crossing the approach path, or operating on the aerodrome. If you hold an Aeronautical Radio Operator Certificate (AROC) you may transmit; without one you may only monitor.
• Keep calls short, standard and in the same format towered calls use — position first, then intention.

Standard CTAF calls for a manned aircraft are made at inbound 5 NM, joining downwind, base, final, and clear of the runway. A remote pilot launching near the circuit should mirror this discipline: call before launch, state position and intent, and call again when clear.

Sample CTAF Call

A sample inbound call from a manned aircraft, which a remote pilot should emulate:

"Cashmore Traffic, Cessna Foxtrot Sierra Golf, inbound five nautical miles, estimating circuit at time two five, runway Two One, Cashmore Traffic."

Note the structure: [location] Traffic (CTAF calls are addressed to all traffic at that aerodrome), [callsign], [position], [intent], and close with the location again so listeners know the call is finished and who it referred to.

For an RPA, an equivalent launch call might be:

"Cashmore Traffic, Remote Pilot Alpha Bravo Charlie Delta, operating remotely one nautical mile north of the field, below 400 feet, runway Two One, Cashmore Traffic."