Design To create the code, a series of international agencies assigned 26 clear-code words (also known as "phonetic words")
acrophonically to the letters of the
Latin alphabet, with the goal that the letters and numbers would be easily distinguishable from one another over radio and telephone. The words were chosen to be accessible to speakers of English, French and Spanish. Some of the code words were changed over time, as they were found to be ineffective in real-life conditions. The final choice of code words for the letters of the alphabet and for the digits was made after hundreds of thousands of comprehension tests involving 31 nationalities. The qualifying feature was the likelihood of a code word being understood in the context of others. For example,
Football has a higher chance of being understood than
Foxtrot in isolation, but
Foxtrot is superior in extended communication. To eliminate national variations in pronunciation, posters illustrating the pronunciation desired by ICAO are available. two spellings deviate from the English norm:
Alfa and
Juliett.
Alfa is spelled with an
f as it is in most European languages because the spelling
Alpha may not be pronounced properly by native speakers of some languages – who may not know that
ph should be pronounced as
f. The spelling
Juliett is used rather than
Juliet for the benefit of French speakers, because they may otherwise treat a single final
t as silent. For similar reasons,
Charlie and
Uniform have recognized alternative pronunciations where the
ch is pronounced "sh" and the
u is pronounced "oo", though these are not present on the NATO chart. Early on, the NATO alliance changed
X-ray to
Xray in its version of the alphabet to ensure that it would be pronounced as one word rather than as two, while the global organization ICAO keeps the spelling
X-ray.
Numerical digits Just as words are spelled out as individual letters, numbers are spelled out as individual digits. That is, 17 is rendered as
one seven and 60 as
six zero. Depending on context, the word
thousand may be used as in English, and, for whole hundreds only (when the sequence 00 occurs at the end of a number), the word
hundred may be used. For example, 1300 is read as
one three zero zero if it is a transponder code or serial number, and as
one thousand three hundred if it is an altitude or distance. The ICAO, NATO, and FAA use modifications of English digits as code words, with 3, 4, 5 and 9 being pronounced
tree,
fower (rhymes with
lower),
fife and
niner. The digit 3 is specified as
tree so that it will not be mispronounced
sri (and similarly
thousand is pronounced
tousand); the long pronunciation of 4 (still found in some English dialects) keeps it somewhat distinct from
for; 5 is pronounced with a second "f" because the normal pronunciation with a "v" is easily confused with "fire"; and 9 has an extra syllable to keep it distinct from the German word
nein "no". (Prior to 1956,
three and
five had been pronounced with the English consonants, but with the vowels broken into two syllables.) For directions presented as the hour-hand position on a clock, the additional numerals "ten", "eleven" and "twelve" are used with the word "o'clock". • Nadazero – from
Spanish or
Portuguese nada + NATO/ICAO zero • Unaone – generic
Romance una, from
Latin ūna + NATO/ICAO one • Bissotwo – from Latin bis + NATO/ICAO two. (1959 ITU proposals bis and too) • Terrathree – from
Italian terzo + NATO/ICAO three ("tree") (1959 ITU proposals ter and tree) • Kartefour – from
French quatre (Latin quartus) + NATO/ICAO four ("fow-er") (1959 ITU proposals quarto and fow-er) • Pantafive – from Greek penta- + NATO/ICAO five ("fife") (from 1959 ITU proposals penta and fife) • Soxisix – from French soix + NATO/ICAO six (1959 ITU proposals were saxo and six) • Setteseven – from Italian sette + NATO/ICAO seven (1959 ITU proposals sette and sev-en) • Oktoeight – generic Romance octo-, from Latin octō + NATO/ICAO eight (1959 ITU proposals octo and ait) • Novenine – from Italian nove + NATO/ICAO nine ("niner") (1959 ITU proposals were nona and niner) The IMO's GMDSS procedures permits the use of either set of code words.
Air traffic control once referred to Taxiway D at the same airport as "Taxiway Dixie", though this practice was officially discontinued in 2020. • "Foxtrot" may be shortened to "Fox" at airports in the United States. • British police use "Indigo" rather than "India". That of the ICAO, first published in 1950 and reprinted many times without correction (e.g. the error in 'golf'), uses a large number of vowels. For instance, it has six low/central vowels: , , , , and . The DIN consolidates all six into the single low-central vowel . The DIN vowels are partly predictable, with the more open vowels in closed syllables and the more close vowels in
open syllables, apart from
echo and
sierra, which have as in English, German and Italian. The DIN also reduced the number of stressed syllables in
bravo and
x-ray, consistent with the ICAO English respellings of those words and with the NATO change of spelling of
x-ray to
xray so that people would know to pronounce it as a single word. There is no authoritative IPA transcription of the digits. However, there are respellings into both English and French, which can be compared to clarify some of the ambiguities and inconsistencies. The
Combined Communications-Electronics Board (CCEB) has code words for punctuation, including those in the table below. Others are: "colon", "semi-colon", "exclamation mark", "question mark", "apostrophe", "quote", and "unquote". ==History==