Numbers

Numbers on the Radio (ICAO Number Pronunciation)

On the radio, numbers are spoken to a standardised scheme to avoid confusion.

Source: ICAO Annex 10 Volume II, Chapter 5.2.3 Pronunciation of Numbers; ICAO Doc 9432.

Standard digit pronunciation

Reading numbers

Individual digits (frequencies, codes)

Digit by digit:

• Frequency 118.450 MHz: "One One Eight Decimal Four Five Zero".
• Squawk 7600: "Seven Six Zero Zero".
• Heading 090°: "Heading Zero Niner Zero".

Frequency abbreviation — important convention

Frequencies with trailing zeros (zeros at the end) are abbreviated:

⭐ Convention for frequencies ending .X00: speak only the significant digits after the decimal (only "Five" instead of "Five Zero Zero").

Thousands (altitudes, visibilities)

Whole thousand: only "thousand" + thousand digit:

• 5000 ft: "Five Thousand".
• 10,000 ft: "One Zero Thousand" or "Ten Thousand".
• 18,000 ft: "One Eight Thousand".

With hundreds: "thousand" + hundred:

• 3500 ft: "Three Thousand Five Hundred".
• 4500 ft: "Four Thousand Five Hundred".
• 5500 ft: "Five Thousand Five Hundred".

Flight Level

Three digits separated:

• FL100: "Flight Level One Zero Zero".
• FL085: "Flight Level Zero Eight Five".
• FL250: "Flight Level Two Five Zero".

Headings (always 3 digits)

• 090°: "Heading Zero Niner Zero".
• 285°: "Heading Two Eight Five".
• 360°: "Heading Three Six Zero" (NOT "North").

Clock direction (clock code)

For traffic advisories the traffic position relative to one's own aircraft is given as a clock time:

• "12 o'clock" = directly ahead → spoken "Twelve o'clock".
• "3 o'clock" = right → "Three o'clock".
• "6 o'clock" = behind → "Six o'clock".
• "9 o'clock" = left → "Nine o'clock".
• "10 o'clock" = forward-left → "Ten o'clock".

→ For clock directions, the phonetic standard (niner for nine) is NOT used; ordinary clock pronunciation is used.

Speeds

• 120 KIAS: "One Two Zero Knots".
• 250 KIAS: "Two Five Zero Knots".

Time (UTC)

Four digits, without colon:

• 16
  UTC: "One Six Two Zero".
• 08
  UTC: "Zero Eight Four Five".
• 00
  UTC: "Zero Zero Zero Zero".

Visibility — unit convention

Visibilities are spoken in different units depending on size (ICAO Annex 3 + Doc 9432):

⭐ Special case 10 km visibility: "One-zero kilometres or more" (standard phrase for 10 km+ visibility without further detail — corresponds to CAVOK threshold).

Example:

• 12 km visibility → "Visibility one zero kilometres or more" (or "one two kilometres").
• 800 m visibility → "Visibility eight hundred metres".

Distances — unit convention

Horizontal distances (cloud separation, traffic distance):

Vertical distances (altitudes, cloud separation vertical): always in feet (ft).

Examples:

• "Cloud horizontal distance two thousand metres" (2000 m horizontal).
• "Cloud vertical distance one thousand feet below" (1000 ft below).

Decimals

For frequencies and QNH the comma is spoken as "decimal":

• 118.450: "One One Eight Decimal Four Five Zero".
• QNH 1013: "QNH One Zero One Three" (no "decimal" because no comma).

QNH pronunciation

• QNH 1013: "QNH One Zero One Three".
• QNH 1025: "QNH One Zero Two Five".

With US AIM (inHg):

• Altimeter 29.92: "Altimeter Two Niner Niner Two".

Example sentences

Common errors

• "Nine" instead of "niner": possible confusion with "no".
• "Hundred" instead of "thousand five hundred": unclear.
• Headings without leading zero: "90°" as "Niner Zero" rather than "Zero Niner Zero".
• Speaking trailing zeros in frequencies: often unnecessary — use abbreviation for .X00.
• Wrong visibility unit: km instead of m for < 5000 m → unprofessional.