Why "special" numbers
In aeronautical radiotelephony, numbers aren't pronounced like in normal conversation. Three examples:
- 3 is not "three" but "Tree" (without the initial "h")
- 5 is not "five" but "Fife" (with f at the end)
- 9 is not "nine" but "Niner" (with an extra syllable)
It seems arbitrary, but there's a precise reason: sound distinguishability. Three and free sound similar in English. Five with a final "v" gets confused with the German number "fünf". Nine is easily confused with German "nein" (no) — a potentially fatal error in a clearance. Niner solves the ambiguity.
Complete table
For decimal numbers on the radio you don't say "point" or "comma". You say "Decimal".
- 118.350 → One One Eight Decimal Three Five Zero - 1013.25 → One Zero One Three Decimal Two Five
Used for frequencies, QNH (rarely), and any number with a decimal point.
How digits are grouped
This is the most important rule, and the one most often broken by beginners. Digits are said one at a time, never as compound numbers.
- 128 is not "one hundred twenty-eight". It's "One Two Eight".
- 2500 is not "twenty-five hundred". It's "Two Five Zero Zero".
- 18000 ft is not "eighteen thousand". It's "One Eight Thousand" (here "thousand" is kept for altitudes).
Exceptions: round altitudes and quantities
For altitudes (in feet) you say "thousand" when the number is in round thousands:
- 3000 ft → Three Thousand
- 5500 ft → Five Thousand Five Hundred
- 8000 ft → Eight Thousand
For Flight Levels (FL) instead, return to single digits:
- FL080 → Flight Level Zero Eight Zero
- FL250 → Flight Level Two Five Zero
HB-PMRClimb Five Thousand Five Hundred feet, QNH One Zero One Eight, HB-PMR.
Radio frequencies
VHF frequencies are always pronounced digit by digit, with "Decimal" before the decimal portion:
- 118.350 → One One Eight Decimal Three Five Zero
- 121.500 → One Two One Decimal Five Zero Zero (VHF emergency frequency)
- 122.075 → One Two Two Decimal Zero Seven Five
On 8.33 kHz channels (increasingly common in Europe), you must read all three digits after the decimal — it's mandatory. "Decimal Three Five" no longer suffices: you need "Decimal Three Five Zero" or "Decimal Three Five Five".
Altitudes, levels, headings, speeds
Each type has its convention:
| Type | Example | Pronunciation |
|---|---|---|
| Altitude in feet | 4500 ft | Four Thousand Five Hundred |
| Flight Level | FL120 | Flight Level One Two Zero |
| Heading | 270° | Heading Two Seven Zero |
| Speed | 110 kt | One One Zero knots |
| QNH | 1013 | One Zero One Three |
| Wind | 230° / 12 kt | Two Three Zero degrees, One Two knots |
Saying "Heading two-seventy" instead of "Heading two seven zero". Sounds natural in plain English, but on the radio it's ambiguous: "two-seventy" can be heard as "two-seven" + something else. Always single digits for headings.
Time check — time on the radio
Time is given in 24-hour format, with digits separated, without "hours" or "minutes":
- 14:30 → One Four Three Zero
- 09:05 → Zero Nine Zero Five
- 23:45 → Two Three Four Five
When context is clear (you're already in flight, not discussing a hypothetical departure time), you can give just the minutes — Three Zero for "at :30". But as a beginner it's safer to always say the full time.
Swiss specifics
On Swiss frequencies you may hear German-speaking pilots saying "null" instead of "Zero" or "acht" instead of "Eight". It's accepted in some local schools, but it's not ICAO standard. If you fly across borders or talk to a controller from another country, you must use the English standard. Skyguide operationally requires ICAO English pronunciation on the radio for international VFR.
Summary — to remember
- Digit by digit, never compound numbers — except round altitudes in thousands/hundreds.
- Tree, Fife, Niner replace Three, Five, Nine.
- "Decimal" for numbers with a decimal point, never "point" or "comma".
- Flight Level is digit by digit; altitudes in feet use "thousand"/"hundred".
- 8.33 kHz frequencies require all three decimal digits.
Sources
- ICAO Doc 9432 — Manual of Radiotelephony, Fourth Edition (2007), Chapter 2
- ICAO Annex 10 — Aeronautical Telecommunications, Volume II
- Aero Locarno · Subject 090 — VFR Communications (EASA syllabus)
- EUROCAE 8.33 kHz — frequency spacing standard
The wiki gives you the parts. The course teaches you to assemble them.
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