🎧

🎧 Communications

The words, numbers and procedures that keep pilots and controllers talking about the same thing — and the physics of the radio wave that carries them. Each chapter opens with the one idea to hold on to, then the phrases, the comparisons that cause most mistakes, and worked examples you can open.

7 chapters 634 linked questions 🧮 Quick tools 📋 Cheat sheet Aircraft-independent

✈️ How to use this guide Each chapter carries the same number as its practice topic. When you get a question wrong, jump to that chapter, read the key idea and the examples, then go back and practise. Radiotelephony is precise wording: the cheat sheet collects the codes and numbers that come up most.

🧰 Quick tools & cheat sheet play with the numbers

Five small helpers for what radiotelephony asks again and again — how far VHF reaches, how a frequency or a call sign is spoken — and a one-screen list of the essentials.

📡 VHF range

Aircraft altitude (ft) Ground aerial height (ft, 0 if not given)

🗣️ Say a frequency

Frequency (MHz)

🔤 Spell a call sign

Registration or call sign

🧭 QDM ⇄ QDR

Bearing given (°) It is a QDM or a QDR

〰️ Wavelength

Frequency (MHz)

📋 Cheat sheet — essentials

Idea	Number / rule
🆘 Distress / urgency	MAYDAY ×3 · PAN PAN ×3
🚨 Transponder	7700 emergency · 7600 radio failure · 7500 unlawful interference
📻 Emergency frequency	121.5 MHz
🔊 Readability	1 unreadable … 5 perfectly readable
📶 Voice band	118–136.975 MHz · AM · 8.33 / 25 kHz
📡 VHF range	1.23 × (√h aerial + √h aircraft) NM
⏱️ Second call	wait at least 10 s
🛬 Final / long final	4 NM · beyond 4 NM (8 NM straight-in)
📵 IFR radio failure	7 min (radar) · 20 min (no radar) · land within 30 min of ETA/EAT
☁️ CAVOK	vis ≥ 10 km · no cloud below 5000 ft or MSA · no CB · no weather
🧭 DF bearing classes	A ±2° · B ±5° · C ±10° · D worse
🕰️ Time	UTC, 24-hour clock, digit by digit

1 Definitions Chapter 1

Radio is a narrow, noisy channel. The alphabet, the way numbers are spoken and the exact meaning of each word are what make a message survive it.

🎯 Phonetic alphabet🎯 Numbers digit by digit🎯 Six-digit frequencies🎯 Frequency bands🎯 Message priority🎯 VHF range

💡 Key idea

Every digit is spoken on its own. 10 is "wun zero", never "ten". Each digit then stands or falls on its own, and one misheard sound cannot change the whole number.

How numbers sound

Digit	Say	Digit	Say
0	ZE-RO	5	FIFE
1	WUN	6	SIX
2	TOO	7	SEV-en
3	TREE	8	AIT
4	FOW-er	9	NIN-er

Decimal is "DAY-SEE-MAL"; hundred and thousand are used for round altitudes, heights and cloud ("wun tousand fife hundred").

Frequencies

📶 Channels were 25 kHz apart; in busy airspace they are split three ways to 8.33 kHz.
🔢 All six digits are passed (132.835), unless the last two are both zero.

Bands

Band	Range
MF	300–3000 kHz
HF	3–30 MHz
VHF	30–300 MHz
UHF	300–3000 MHz

Message priority

Distress (MAYDAY)
Urgency (PAN PAN), including medical transports
Direction finding
Flight safety
Meteorological
Flight regularity

Service hours

H24 continuous · HJ sunrise to sunset · HN sunset to sunrise · HS scheduled hours · HO as needed · HX no fixed hours.

Worked example — VHF range

An aircraft at 10 000 ft talks to an aerial 400 ft high. Range ≈ 1.23 × (√400 + √10 000) = 1.23 × (20 + 100) ≈ 148 NM. Ignoring the aerial gives 123 NM.

2 General Operating Procedures Chapter 2

Technique, call signs, standard words, read-back and the radar instructions every pilot hears.

🎯 Speaking technique🎯 Time🎯 Standard words🎯 Call sign types🎯 Read-back🎯 Conditional clearances

💡 Key idea

Read back anything that, if misheard, could put the aircraft in the wrong place — clearances, levels, headings with the direction of turn, speeds, runways, frequencies and squawks — and end the read-back with your call sign.

Technique

🗣️ About 100 words per minute; slower when the other station must write it down.
⏳ Listen before transmitting; wait at least 10 seconds before calling again.
🕰️ UTC, 24-hour clock: 0803 is "zero tree" or "zero ait zero tree".

Words that mean exactly one thing

ROGER

I have received all of your last transmission. Never an answer to a question.

WILCO

I understand and will comply.

AFFIRM / NEGATIVE

Yes / no (or permission not granted).

STANDBY

Wait and I will call you. Not an approval or a refusal.

Call signs

Type	Full	Abbreviated
A	Registration: G-BODA, N57826	First character + at least last two: G-DA, N26
B	Telephony designator + last four of registration	Designator + last two
C	Telephony designator + flight number: Northwind 937	Not abbreviated

Only the ground station may abbreviate first; the pilot follows.

Direction finding

🧭 QDM: magnetic heading to steer to the station (zero wind). QDR: magnetic bearing from it. They differ by 180°.
🎯 Bearing classes: A ±2°, B ±5°, C ±10°, D worse.

Radar and conditional clearances

↩️ "Left heading 300" — the direction of turn is part of the read-back.
🔁 "Orbit right" means keep orbiting until told; "one orbit right" means one 360°.
⚡ "Avoiding action" means turn now: there is a risk of collision.
⏸️ Conditional clearance: call sign, condition, clearance, condition again — "behind the landing Airbus, line up and wait, behind".

🧠 Memory hook ROGER says "heard it", WILCO says "doing it". Never say both — WILCO already includes ROGER.

3 Phraseology Chapter 3

The standard words for each phase of a flight, from the start-up call to the vacated runway.

🎯 Levels🎯 Position reports🎯 Taxi and take-off🎯 Circuit calls🎯 Approach clearances🎯 ACAS reports

💡 Key idea

"Take-off" is said only when the aircraft is cleared to take off (or the clearance is cancelled). Everywhere else the word is "departure", so a stray "take-off" can never be mistaken for a clearance.

Levels

⬆️ "Climb to FL120", "descend to altitude 3000 feet".
🚀 "Expedite climb" — best practicable rate.
📍 "Cross KELBY at or above FL110" — any level from FL110 upwards.
🛰️ ACAS: report "TCAS RA" when manoeuvring, then "clear of conflict, returning to …".

On the ground

🚜 Request start-up and push-back; read back the taxi route and every hold short instruction.
🛫 "Line up and wait", "cleared for take-off", "cancel take-off — I say again, cancel take-off".
🔁 "Go around" is read back; the pilot says "going around".

Circuit calls

Downwind

Abeam the upwind end of the runway.

Final

Within 4 NM of touchdown.

Long final

Turning final beyond 4 NM, or at 8 NM on a straight-in approach.

Weather and approach

💨 Wind: mean direction and speed, plus variations: "270 degrees 15 knots gusting 25".
🛬 "Cleared ILS approach runway 27"; "report established on the localiser".
7️⃣ Squawk 7000 is the general conspicuity code in many regions when no code is assigned.

4 Weather Information Chapter 4

Where weather comes from in flight — ATIS, VOLMET, reports from ATC — and how it is spoken.

🎯 ATIS🎯 VOLMET🎯 Cloud amounts🎯 Visibility units🎯 CAVOK🎯 Braking action

💡 Key idea

ATIS is for one aerodrome and has a letter; VOLMET is for several aerodromes and runs on a loop. Acknowledge the ATIS letter on first contact so ATC knows you have it.

Cloud amounts

Term	Oktas
FEW	1–2
SCATTERED	3–4
BROKEN	5–7
OVERCAST	8

👁️ Visibility in metres below 5 km, in kilometres from 5 km up.
☀️ CAVOK: visibility 10 km or more, no cloud below 5000 ft or the highest MSA (whichever is higher), no cumulonimbus, no significant weather.
🛞 Braking action may be passed as a measured coefficient (0.37 → "37") or a band from good to poor.

Worked example — is it CAVOK?

Visibility 15 km, scattered cloud at 6000 ft, highest MSA 6500 ft. The cloud is below the MSA, which is higher than 5000 ft, so it is not CAVOK.

5 Failures and Emergencies Chapter 5

Distress, urgency, radio failure and unlawful interference: what to say, where, and who keeps quiet.

🎯 Distress and urgency🎯 The distress message🎯 Imposing silence🎯 Medical transports🎯 Radio failure🎯 7500

💡 Key idea

Distress is grave and imminent danger needing immediate help; urgency is a serious concern that does not. MAYDAY three times for one, PAN PAN three times for the other.

The distress message

MAYDAY MAYDAY MAYDAY
Station addressed (if time allows)
Call sign
Nature of the emergency
Intentions of the commander
Position, level and heading
Any other useful information

📻 Use the frequency in use first; 121.5 MHz if needed.
🤫 The station controlling the distress imposes silence: "Stop transmitting — MAYDAY". It ends with "distress traffic ended".
🚑 "PAN PAN MEDICAL" marks a protected medical transport.
📟 Squawk 7700 for an emergency, 7600 for radio failure, 7500 for unlawful interference.

6 IFR Communications Chapter 6

Instrument flight brings position reports, weather reports from the aircraft, SELCAL and the radio failure procedure.

🎯 HEAVY in the call sign🎯 Level reports🎯 Position report🎯 Air-report sections🎯 Radio failure🎯 SELCAL

💡 Key idea

With radio failure, be predictable. Squawk 7600, hold the last speed and level for 7 minutes (radar) or 20 minutes (no radar), then fly the flight plan, start the approach at the expected time and land within 30 minutes.

🐘 Heavy aircraft (136 000 kg or more) add "HEAVY" on first contact.
📏 Level is reported as a flight level on standard pressure, as an altitude on QNH.
🚫 "Unable" plus the reason when an instruction cannot be followed.

Position report

Call sign · position · time · level · next position and time · ensuing significant point. The last three may be left out when the controller allows.

Air-report sections

Section 1

Position: call sign, position, time, level, next point.

Section 2

Operational: ETA, endurance.

Section 3

Weather: temperature, wind, turbulence, icing, humidity.

SELCAL sends four audio tones, about 2 seconds long, so the crew need not listen to HF all the time.

7 VHF Propagation Chapter 7

Why VHF is line of sight, how far it reaches, and what spoils it.

🎯 Speed and wavelength🎯 The bands🎯 118–136.975 MHz🎯 AM and bandwidth🎯 Line of sight🎯 Ducting

💡 Key idea

Above about 30 MHz the only useful path is the direct (space) wave. Range is set by height: 1.23 × (√h₁ + √h₂) NM, with heights in feet.

⚡ Radio waves travel at about 300 000 km/s (about 162 000 NM per second).
〰️ Wavelength = 300 / frequency in MHz (metres): 120 MHz → 2.5 m.
📶 Voice 118–136.975 MHz, navigation 108–117.95 MHz, broadcast FM 88–107.95 MHz.
🎚️ VHF voice uses double-sideband AM (A3E); 5 kHz of audio needs 10 kHz of bandwidth.
🌫️ A temperature inversion can trap the wave in a duct and carry it far beyond normal range.
🔇 Two equal waves 180° out of phase cancel completely.

Worked example — aerial height

An aircraft at 2500 ft needs 100 NM. 100 / 1.23 = 81.3. The aircraft term is √2500 = 50, so √h₁ = 31.3 and the aerial must be about 980 ft high.