ICAO phonetic alphabet: how letters and numbers sound on aviation radio

You are standing at the fence with the tower frequency in your ear, and somewhere between two landing clearances you hear a line like “Delta Echo Alfa Bravo Charlie, runway two six left, cleared to land”. If you know the ICAO phonetic alphabet and how numbers are pronounced on aviation radio, you know right away: it means the aircraft registered D-EABC, and it is landing on runway 26L. This guide explains all 26 letter words, the special number words like Tree and Niner, and the rules for how altitudes, flight levels, frequencies, squawks and times are spoken. After that, the radio no longer sounds like a code but like a language you can read.

The short answer

The ICAO phonetic alphabet assigns a fixed word to each of the 26 letters – from Alfa for A to Zulu for Z. In addition there are fixed pronunciations for the digits: Zero, One, Two, Tree, Fower, Fife, Six, Seven, Eight, Niner, plus Decimal, Hundred and Thousand. The basis is Annex 10 to the Convention on International Civil Aviation, supplemented in Europe by the common rules of the air (SERA). The goal is simple: over a noisy radio, with an accent, under time pressure, every piece of information has to get through the first time.

The alphabet from Alfa to Zulu

Here is the complete chart with a pronunciation guide. The phonetic respelling follows the pronunciation guides of aviation authorities, with the stressed syllable in capital letters.

Letter	Word	Pronunciation (rough)	Letter	Word	Pronunciation (rough)
A	Alfa	AL-fah	N	November	no-VEM-ber
B	Bravo	BRAH-voh	O	Oscar	OSS-kah
C	Charlie	CHAR-lee or SHAR-lee	P	Papa	pah-PAH
D	Delta	DELL-tah	Q	Quebec	keh-BECK
E	Echo	ECK-oh	R	Romeo	ROW-mee-oh
F	Foxtrot	FOKS-trot	S	Sierra	see-AIR-rah
G	Golf	GOLF	T	Tango	TANG-go
H	Hotel	hoh-TELL	U	Uniform	YOU-nee-form or OO-nee-form
I	India	IN-dee-ah	V	Victor	VIK-tah
J	Juliett	JEW-lee-ETT	W	Whiskey	WISS-key
K	Kilo	KEY-loh	X	X-ray	ECKS-ray
L	Lima	LEE-mah	Y	Yankee	YANG-key
M	Mike	MIKE	Z	Zulu	ZOO-loo

A few stumbling blocks you will run into when listening in:

• Papa and Hotel are stressed on the second syllable, and Quebec is pronounced like the Canadian city in French – so without a “kw”.
• Alfa and Juliett look misspelled but are not. The f in Alfa keeps anyone from not reading the ph as an f, and the double t in Juliett makes sure French speakers do not swallow the end of the word. The British radio manual CAP 413, by the way, writes Alpha – on the radio both sound identical.
• Charlie and Uniform each have two permitted pronunciations. On the radio you hear both.

Numbers on aviation radio: Tree, Fower, Fife and Niner

For digits, radio pronunciation departs from normal English in four places. The reason is the same each time: avoid confusion and sidestep sounds that not every speaker can pronounce cleanly.

Digit	Radio word	Why?
0	Zero	–
1	One (WAN)	–
2	Two (TOO)	–
3	Tree	the English th is hard for many speakers, “tree” is unambiguous
4	Fower	two syllables, so it does not sound like “for”
5	Fife	clearly set apart from “fire”
6	Six	–
7	Seven	–
8	Eight (AIT)	–
9	Niner	two syllables, so it does not sound like the German “nein”
, / .	Decimal (DAY-SEE-MAL)	separates the digits after the point, whether point or comma
100	Hundred	only for round hundreds
1000	Thousand (TOW-SAND)	likewise without the th

German-language radio has a peculiarity of its own: two is pronounced “Zwo”, so that it stands out clearly from “drei” (three). Letters, on the other hand, are spelled with the ICAO alphabet in German, too. When radio is spoken in German and when in English is explained in the article English or German on aviation radio.

When digit by digit, when Hundred and Thousand?

The most important rule for numbers on the radio is: as a rule, every digit is spoken individually. There is an exception only for round hundreds and thousands in certain items. The basic rule applies to:

• Callsigns with a flight number: BAW246 is “Speedbird Two Fower Six”
• Flight levels: FL180 is “Flight Level One Eight Zero”
• Headings and wind directions: “heading one fife zero”, wind “one fife zero degrees, one eight knots”
• Air pressure (QNH): 1013 hPa is “QNH One Zero One Tree”
• Frequencies: “one two two decimal one”
• Runways: 26L is “runway Two Six Left”

The exception applies to altitudes, cloud bases, visibilities and runway visual range (RVR) when the number consists of round hundreds or thousands. Then the digits are followed by the word Hundred or Thousand:

Item	Spoken	Rule
2,500 ft	Two Thousand Fife Hundred	round thousands and hundreds
11,000 ft	One One Thousand	thousands place digit by digit, then Thousand
25,000 ft	Two Fife Thousand	as above
FL100	Flight Level One Hundred	round-hundred flight level
FL180	Flight Level One Eight Zero	otherwise always individually
QNH 1000 hPa	One Thousand	special case under SERA
Squawk 1000	One Thousand	special case under SERA

Notably, 11,000 feet is not “eleven thousand” but “one one thousand”. So here, too, it stays with single digits before the word Thousand – compound English number words do not occur on the radio.

In German radio it works the same way: round hundreds and thousands are spoken together (“zwotausendvierhundert Fuß”), everything else digit by digit (“Steuerkurs zwo-eins-null”, “Piste zwo-sieben”).

Frequencies: six digits and Decimal

Frequencies are always given with all six digits – regardless of whether they are in the classic 25 kHz spacing or the narrower 8.33 kHz spacing. If the last two digits are zero, the first four are enough.

Frequency	Spoken
118.125	One One Eight Decimal One Two Fife
119.050	One One Niner Decimal Zero Fife Zero
122.500	One Two Two Decimal Fife
118.000	One One Eight Decimal Zero

In the 8.33 kHz spacing, by the way, the number given is a channel designation and not always exactly the physical transmit frequency. On the radio, though, nobody says “channel” – you simply read out the six digits. How the spacing works and why it was introduced is covered in the article on 8.33 kHz channel spacing. Which frequencies at an airport are responsible for Delivery, Ground, Tower and Approach is shown in the guide Understanding aviation radio frequencies.

For you as a listener, that means: when the tower says “contact Approach one one niner decimal zero fife zero”, you can punch the frequency straight into your scanner or your app and follow the aircraft.

Times and squawks

Times are given in UTC on aviation radio. Usually the minutes are enough: 08:23 becomes “two tree”, and the hour is only added when there is a risk of confusion (“zero eight two tree”). Time announcements begin with the word “Time”. Midnight is 2400 as the end of one day and 0000 as the start of the next. When comparing with your watch, remember that in Central Europe UTC is one hour behind local time in winter and two hours behind during daylight saving time.

Transponder codes have four digits and are generally spoken digit by digit, for example “squawk six fife zero zero”. Hopefully you will rarely hear the emergency codes; what is behind 7500, 7600 and 7700 is explained in the article Squawk codes 7500, 7600, 7700. How the transponder itself works is covered under Transponder Mode A, C and S.

Registrations and callsigns on the radio

For spotters this is the most exciting part, because it holds the information on which aircraft is speaking right now. There are essentially two kinds of callsigns:

• Registration as callsign: Small aircraft, business jets and many factory or ferry flights report with their registration. D-EABC becomes “Delta Echo Alfa Bravo Charlie”. How registrations are structured and what the letters reveal is explained in the guide Understanding aircraft registrations – and for Germany specifically in German aircraft registrations.
• Airline callsign plus flight number: Scheduled flights use a radio callsign of the airline. British Airways reports as “Speedbird”, for instance, Lufthansa as “Lufthansa”. The flight number follows, digit by digit. Why callsign and flight number do not always match is covered in the article Callsign and flight number, and curious callsigns are in Airline callsigns and their history.

How registrations are abbreviated

At first contact, both sides state the full callsign. After that, the ground station may abbreviate if there is no risk of confusion – the pilot follows only afterwards. For registrations the rule is: the first character plus at least the last two.

Full callsign	Abbreviated
D-EABC	Delta Bravo Charlie
G-ABCD	Golf Charlie Delta
PH-ABC	Papa Bravo Charlie
Piper G-BSZT	Piper Zulu Tango
Speedbird 246	not shortened

As the Piper example shows, the manufacturer, the model or the aircraft category may precede the registration. US registrations with N are abbreviated by a pattern of their own. With very similar registrations on one frequency, ATC can order a return to the full callsign.

Large aircraft add their wake turbulence category at first contact: “Heavy” for heavy types like the Boeing 747-400, “Super” for the Airbus A380. So if you hear “Super” after a callsign, it is worth looking up.

Where the alphabet comes from

Before today’s alphabet, aviation used a heavily English-oriented chart that began with “Able, Baker”. For pilots and controllers whose first language was not English, it was only partly suitable. In the late 1940s ICAO therefore commissioned linguists at the Université de Montréal under the linguist Jean-Paul Vinay to develop an alphabet that works in as many languages as possible.

The first version took effect in the early 1950s but showed weaknesses in everyday use: individual word pairs could be confused, such as Delta and Extra or Nectar and Victor. After further tests with speakers from more than 30 countries, five words were replaced:

Letter	1951 version	Current version
C	Coca	Charlie
M	Metro	Mike
N	Nectar	November
U	Union	Uniform
X	Extra	X-ray

This version has been in force since 1956 and has not changed since. NATO adopted it the same year, the International Telecommunication Union (ITU) by 1959 at the latest, and maritime shipping followed later. That is why the alphabet is called the ICAO, NATO or international spelling alphabet depending on the setting – the same chart is always meant.

Why the rules are so strict

Radio is a shared medium: only one person speaks at a time, quality varies, and many of those involved speak English as a foreign language. Standardized words and numbers are therefore a central building block of flight safety. On top of that comes the readback requirement: the pilot reads back clearances, altitudes, headings, runways, frequencies and squawks so that the controller notices errors immediately. If something is said wrong, “correction” follows, and if something is unclear, “say again”.

How important unambiguous wording is shows in aviation history. After the Tenerife disaster of 1977, radio phraseology was tightened in several respects. More on standard words like Roger, Wilco, Affirm and Negative is in the article Radio phraseology, and distress calls are covered under Mayday and Pan-Pan.

Understanding the radio in 5 steps

Where you can listen in at all is shown in the articles Listening to aviation radio online and Buying an aviation radio scanner, or alternatively with an SDR stick. Before you switch on, be sure to read what the law says about listening to aviation radio – listening in and passing on content are not the same thing.

Typical radio calls decoded

To finish, a few examples of what you might hear at a large airport like Frankfurt or Munich. The callsigns are fictional.

Heard	Meaning
“Delta Echo Alfa Bravo Charlie, squawk fower six two one”	D-EABC, set transponder code 4621
“Descend altitude four thousand feet, QNH one zero zero eight”	descend to 4,000 feet, air pressure 1008 hPa
“Climb flight level one hundred”	climb to flight level 100
“Wind two seven zero degrees, one two knots, runway two fife right, cleared to land”	wind from 270 degrees at 12 knots, cleared to land on runway 25R
“Contact Tower one one niner decimal niner”	switch to the tower on 119.900
“Taxi via Lima, Mike, holding point runway two six left”	taxi via taxiways L and M to the holding point of runway 26L

Taxiway names in particular are almost always spelled out – how they are assigned is explained in the article Taxiways, holding points and signs. If you listen in at a spot like the Munich Airport visitors’ hill (Besucherhügel) and know the taxiways, you often already know beforehand where an aircraft is about to appear.

Conclusion

The ICAO phonetic alphabet is the key to aviation radio. 26 fixed words, four unusual number words and a handful of rules are enough to understand registrations, runways, altitudes, frequencies and squawks with confidence. The basic rule: digits individually, only round hundreds and thousands together for altitudes and visibilities, frequencies always six digits. For spotters it pays off twice – if you understand the radio, you know sooner what is coming and can match your sightings cleanly.