Every transmission in this subject is assembled from the same parts: letters spelled to a fixed alphabet, numbers spoken to fixed rules, time in a fixed reference, and a vocabulary of standard words whose meanings ICAO has nailed down in Annex 10, Volume II. This lesson is those parts. Learn them precisely: the exam's favourite questions are the exceptions, the flight level that is spoken as a word rather than digits, and the reply that sounds polite but is procedurally wrong.
The spelling alphabet
When proper names, service abbreviations and words of doubtful spelling are spelled out in radiotelephony, the ICAO spelling alphabet is used; when there is no risk to correct reception, spelling is dispensed with to keep the frequency moving. The twenty-six words:
Alfa, Bravo, Charlie, Delta, Echo, Foxtrot, Golf, Hotel, India — note the spelling Alfa, with an f, not Alpha;
Juliett, Kilo, Lima, Mike, November, Oscar, Papa, Quebec, Romeo — note Juliett, with a double t;
Sierra, Tango, Uniform, Victor, Whiskey, X-ray, Yankee, Zulu — the two odd spellings above are the exam's favourite catch.
Transmitting numbers
The base rule: every digit is pronounced separately. Call signs, headings, wind, runway designators and transponder codes are all read digit by digit: heading 100 is "heading one zero zero", runway 27 is "runway two seven". The English pronunciations are shaped for clarity through noise: ZE-RO, WUN, TOO, TREE, FOW-er, FIFE, SIX, SEV-en, AIT, NIN-er, with the decimal point spoken as DAY-SEE-MAL and 121.5 read "one two one decimal five". The exceptions, where HUNDRED and THOUSAND enter, are a fixed list:
Flight levels — digits, except whole hundreds: FL 180 is "flight level one eight zero", but FL 200 is "flight level two hundred".
Altimeter settings — digits, except 1,000 hPa, which is "one thousand": QNH 1009 is "one zero zero nine".
Transponder codes — digits, except whole thousands: squawk 2400 is "two four zero zero", squawk 2000 is "two thousand".
Altitude, cloud height, visibility and RVR — whole hundreds and thousands are spoken with the words: 800 is "eight hundred", 12,000 is "one two thousand", and 3,400 combines as "three thousand four hundred".
Relative bearings on the clock — traffic information uses TEN, ELEVEN or TWELVE o'clock, the one place double digits are spoken as words.