Who uses it,
and what the rules say.

The UK CAA’s CAP 413 says callsigns, headings, wind speeds, frequencies and most flight levels are said digit by digit, while whole hundreds and thousands in altitudes, heights and visibility use HUNDRED or TOUSAND. UK CAA, CAP 413 ↗

A slight pause before and after numbers makes them easier to understand. UK CAA, CAP 413 ↗

In CAP 413, a radio frequency of 122.500 is said “WUN TOO TOO DAY SEE MAL FIFE”. UK CAA, CAP 413 ↗

In the US, the dot in a radio frequency is said “point”; the FAA notes that ICAO procedures require “decimal”. FAA, Aeronautical Information Manual 4-2 ↗

The US FAA tells its flight service staff to use the ICAO pronunciation of numbers and, as necessary, individual letters for clarity. FAA, JO 7110.10 ↗

US controllers are told: “Use the ICAO pronunciation of numbers and individual letters.” FAA, JO 7110.65 ↗

The FAA uses the ICAO phonetic alphabet when conditions mean a message can’t easily be received without it. FAA, Aeronautical Information Manual 4-2 ↗

CAP 413 explains that ICAO sets out standard international radio phrases in several documents, including Annex 10 Volume 2 (Communications Procedures). UK CAA, CAP 413 ↗

For UK pilot exams, the radio syllabus is drawn directly from ICAO Annex 10 Volume 2 and ICAO Doc 9432 (the Manual of Radiotelephony), not from CAP 413. UK CAA, CAP 413 ↗

US pilots should use the phonetic alphabet to identify their aircraft when they first call air traffic control. FAA, Aeronautical Information Manual 4-2 ↗

A typical first call in the FAA’s manual: “New York Radio, Mooney Three One One Echo.” FAA, Aeronautical Information Manual 4-2 ↗

US-registered civil aircraft are called with the prefix “November”, then the ICAO pronunciation of their registration, for example “November One Two Three Four Golf”. FAA, JO 7110.65 ↗

Controllers may ask pilots to use the code words when aircraft with similar-sounding callsigns are on the same frequency. FAA, Aeronautical Information Manual 4-2 ↗

In the UK, student pilots flying solo use the callsign prefix “STUDENT” on their first call. UK CAA, CAP 413 ↗

In US practice, 10,000 is said “one zero thousand”. FAA, Aeronautical Information Manual 4-2 ↗

A serial number such as 11,495 is said “One one four niner five”. FAA, JO 7110.65 ↗

Controllers may repeat a number in a second form for clarity: “One Seven Thousand, Seventeen Thousand.” FAA, JO 7110.65 ↗

At and above 18,000 feet in the US, heights are given as flight levels: 190 is “Flight Level One Niner Zero”. FAA, Aeronautical Information Manual 4-2 ↗

A US airway such as V12 is said “Victor Twelve”. FAA, Aeronautical Information Manual 4-2 ↗

Headings are magnetic; the word “true” must be added when it applies. FAA, Aeronautical Information Manual 4-2 ↗

A speed of Mach 0.64 is said “Mach point six four”. FAA, Aeronautical Information Manual 4-2 ↗

The FAA uses Coordinated Universal Time (UTC), and the word “Zulu” may be used for UTC. FAA, Aeronautical Information Manual 4-2 ↗

So 0920 UTC is said “zero niner two zero”. FAA, Aeronautical Information Manual 4-2 ↗

When giving the time, usually only the minutes are needed, and UTC is used unless stated otherwise. UK CAA, CAP 413 ↗

2400 means midnight at the end of the day, and 0000 the beginning of the day. UK CAA, CAP 413 ↗

The UK CAA advises an even rate of speech of no more than 100 words per minute. UK CAA, CAP 413 ↗

Avoid hesitation sounds such as “er”. UK CAA, CAP 413 ↗

When reception is likely to be difficult, important parts of a message should be said twice. UK CAA, CAP 413 ↗

Its first piece of advice: listen before you transmit. FAA, Aeronautical Information Manual 4-2 ↗

The FAA says jargon, chatter and “CB” slang have no place in air traffic control talk. FAA, Aeronautical Information Manual 4-2 ↗

A transmitter left switched on by mistake is known as a “stuck mike”. FAA, Aeronautical Information Manual 4-2 ↗

Radio checks use a readability scale from 1 (unreadable) to 5 (perfectly readable). UK CAA, CAP 413 ↗

The FAA’s phonetic alphabet table also lists the Morse code for every letter and number. FAA, Aeronautical Information Manual 4-2 ↗

NATO’s review of the IATA alphabet in the mid-1950s was led by the United Kingdom and the United States. NATO ↗

In 1941 the United States adopted the Joint Army/Navy “Able Baker” alphabet across all its military branches; two years later the Royal Air Force decided to use it too. NATO ↗

The Royal Air Force used at least two different alphabets; the one it used from 1921 to 1942 began Ace, Beer, Charlie. University of York ↗

ACP 125(G) is dated 28 November 2016. ACP 125(G) ↗

The allied radiotelephone manual ACP 125(G) says each letter has a uniquely pronounced word so it is said the same way every time. ACP 125(G) ↗

ACP 125(G) gives 9 as NINE-ER and 5 as FIFE. ACP 125(G) ↗

Before spelling a word, military operators say the proword “I SPELL”. ACP 125(G) ↗

In military procedure, numbers are sent figure by figure after the proword FIGURES, to set them apart from words that sound alike. ACP 125(G) ↗

Standard prowords are used in place of whole sentences to keep voice messages short and clear. ACP 125(G) ↗

Every military transmission ends with either OVER or OUT. ACP 125(G) ↗

Military time checks are given in Greenwich Mean Time, also called ZULU time. ACP 125(G) ↗

The UK’s Distress and Diversion Section is at the London Control Centre and is staffed by RAF controllers. UK CAA, CAP 413 ↗

At sea, the IMO Standard Marine Communication Phrases (adopted 29 November 2001) say that when spelling is necessary, only their spelling table should be used. IMO Standard Marine Communication Phrases ↗

The IMO notes that a few digits have a modified pronunciation compared with everyday English. IMO Standard Marine Communication Phrases ↗

The IMO table says 1000 as TOUSAND. IMO Standard Marine Communication Phrases ↗

The IMO phrases list MAYDAY to announce a distress message and PAN PAN to announce an urgency message. IMO Standard Marine Communication Phrases ↗

A ship’s urgency call is PAN PAN three times, then ALL STATIONS three times. IMO Standard Marine Communication Phrases ↗

IMO rules require English as the working language on a ship’s bridge for bridge-to-bridge and bridge-to-shore calls. IMO Standard Marine Communication Phrases ↗

In 1973 an IMO committee agreed that where language difficulties arise, English should be used for navigation. IMO Standard Marine Communication Phrases ↗

Before the current phrases there was the Standard Marine Navigational Vocabulary, adopted in 1977 and amended in 1985. IMO Standard Marine Communication Phrases ↗

At sea, eight “message markers” can start a message, such as QUESTION, ADVICE, WARNING and INTENTION. IMO Standard Marine Communication Phrases ↗

Instead of “May I enter the fairway?”, the IMO phrases say: “QUESTION. Do I have permission to enter the fairway?” IMO Standard Marine Communication Phrases ↗

At sea, numbers are spoken in separate digits: 150 is “one-five-zero”. IMO Standard Marine Communication Phrases ↗

The exception is rudder angles in wheel orders, which are said as whole numbers, such as “fifteen”. IMO Standard Marine Communication Phrases ↗

Times at sea should be given in the 24-hour UTC notation. IMO Standard Marine Communication Phrases ↗

To fix an error, say “Mistake”, then “Correction” and the corrected part. IMO Standard Marine Communication Phrases ↗

If a message isn’t properly heard, say “Say again (please)”. IMO Standard Marine Communication Phrases ↗

Ships identify themselves with their 9-digit MMSI number, plus name or call sign. IMO Standard Marine Communication Phrases ↗

A set of signal flags has 26 letter flags, 10 number pennants, 3 substitutes and the answering pennant. International Code of Signals (Pub. 102) ↗

The code’s spelling tables are for radio and for voice over a loud hailer. International Code of Signals (Pub. 102) ↗

In the code’s figure words, such as Nadazero and Unaone, the second part is the word used in aviation. International Code of Signals (Pub. 102) ↗

The word INTERCO, said IN-TER-CO, means International Code groups follow. International Code of Signals (Pub. 102) ↗

CORRECTION, said KOR-REK-SHUN, means “Cancel my last word or group.” International Code of Signals (Pub. 102) ↗

The code’s distress call is “Mayday Mayday Mayday. This is…” followed by the ship’s name or call sign three times. International Code of Signals (Pub. 102) ↗

Flag A: “I have a diver down; keep well clear at slow speed.” International Code of Signals (Pub. 102) ↗

Flag C means “Yes”. International Code of Signals (Pub. 102) ↗

Flag E: “I am altering my course to starboard.” International Code of Signals (Pub. 102) ↗

Flag O: “Man overboard.” International Code of Signals (Pub. 102) ↗

Flag U: “You are running into danger.” International Code of Signals (Pub. 102) ↗

Flag V: “I require assistance.” International Code of Signals (Pub. 102) ↗

Flag Y: “I am dragging my anchor.” International Code of Signals (Pub. 102) ↗

Flag Z: “I require a tug.” International Code of Signals (Pub. 102) ↗

According to NATO, it became the universal phonetic alphabet for military, civilian and amateur radio communications. NATO ↗

The alphabet is set out in Appendix 14 of the ITU Radio Regulations, “Phonetic alphabet and figure code”, which says the table shall be used when it is necessary to spell out call signs, service abbreviations and words. ITU Radio Regulations, Appendix 14 ↗

The ITU table is used “when it is necessary to spell out call signs, service abbreviations and words”. ITU Radio Regulations, Appendix 14 ↗

Appendix 14 was last revised at the World Radiocommunication Conference of 2007 (WRC-07). ITU Radio Regulations, Appendix 14 ↗

Most of the 2020 edition of the Radio Regulations came into force on 1 January 2021. ITU Radio Regulations, Appendix 14 ↗

The ITU gives two ways to say C (CHAR LEE or SHAR LEE) and two for U (YOU NEE FORM or OO NEE FORM). ITU Radio Regulations, Appendix 14 ↗