3.4 Transmission of Numbers

3.4 Transmission of Numbers

Quick Answer: Under RIC-21 §5.4, say each digit of a number unless it is a whole thousand—then say each digit of the thousands count followed by “thousand.” Use ICAO-style digit words (WUN, TREE, FOW-er, FIFE, NIN-er, etc.), say “decimal” for points, and apply special patterns for altitudes, flight levels, headings, field elevation, wind/cloud groups, and money.

Numbers carry altitudes, runways, frequencies, winds, and times. Mis-speaking a single digit can put traffic at the wrong level or on the wrong heading. This section is pure procedure: learn the rule, the pronunciation table, and the worked examples printed in RIC-21.

Core rule: digit-by-digit, except whole thousands

All numbers except whole thousands should be transmitted by pronouncing each digit separately.

Whole thousands should be transmitted by pronouncing each digit in the number of thousands followed by the word “thousand.”

Official examples (RIC-21 §5.4)

Study notes:

• 100 is not “one hundred” in the general digit rule example—it is one zero zero. (Altitude phraseology, below, does use “thousand” and “hundred” as quantity words in a different pattern.)
• 5,800 is not a whole thousand, so every digit is spoken: five eight zero zero.
• 11,000 is a whole thousand quantity (eleven thousands): one one thousand, not “one one zero zero zero” and not “eleven thousand” as a civilian phrase.
• 68,009 mixes thousands scale with leftover digits: six eight zero zero nine (digit-by-digit because it is not a whole thousand alone).

If a number is exactly N × 1000 (11,000; 5,000; 20,000), use the whole-thousands pattern. If any non-zero digit exists outside pure thousands (5,800; 68,009), fall back to separate digits for the full string as in the table.

Digit and related pronunciations

RIC-21 §5.3/§5.4 standard pronunciations (learn these exact forms):

Why the odd forms? Tree, fife, and niner reduce confusion with “free,” “fire,” and German “nein” / English “nine” under noise. Wun and too separate “one” from “on” and “two” from “to/too.” Exam answers should reflect these radiotelephony forms when pronunciation is tested.

Decimals

Numbers containing a decimal point are transmitted digit-by-digit with the point spoken as “decimal.”

Emergency frequency 121.5 MHz is a classic ROC-A number: always “one two one decimal five,” never “one twenty-one point five” in standard procedure.

Monetary amounts

Monetary denominations transmitted with groups of digits should be sent in the sequence in which they are written.

Note the leading “dollars” when the currency word appears in the written form, and the use of decimal for the cents separator in the examples.

Altitude and flight level

Altitude above sea level should be expressed in thousands plus hundreds of feet. Separate digits shall be used to express flight levels.

Contrast carefully:

• Altitude 2,700 ft uses quantity words thousand and hundred in the altitude pattern.
• FL265 is not “flight level two hundred sixty-five”; it is digit-by-digit: two six five.

Field elevation (below) is yet another pattern: prefix “field elevation” and then the number in the form shown by RIC-21.

Group forms: flights, types, wind, cloud

Aircraft type numbers, wind speed, and cloud formation heights are expressed in group forms (not always pure digit strings).

Wind groups: direction is three digits (270 → two seven zero degrees) and speed is digit-by-digit (10 → one zero knots). Cloud height in the 34BKN example is grouped as a height phrase (“Thirty Four Hundred”) plus the coverage term (“Broken”), not as “three four bravo kilo november.”

These group forms are easy exam discriminators: if the question shows Wind 270/10, the correct spoken form includes degrees and knots as in the circular.

Time groups (spoken)

Time is Coordinated Universal Time (UTC) in the §5.4 examples:

Link back to §5.2: the structure is four figures (or minutes past the hour when abbreviated that way); §5.4 is the voice of those figures, including niner and zulu.

Aircraft headings: three digits, magnetic vs true

Aircraft headings are given in groups of three digits.

• If operating within the Southern Domestic Airspace (SDA), the heading is expressed in degrees magnetic.
• If operating within the Northern Domestic Airspace (NDA), the heading is expressed in degrees true.

Always pad to three digits (005, not “five”). The SDA/NDA magnetic-vs-true rule is a favorite Canadian exam point—do not assume magnetic everywhere in Canada.

Aerodrome (field) elevation

Aerodrome elevations are expressed in feet, prefixed by the expression “field elevation.”

Notice 3500 combines a thousands quantity with trailing digits: “three thousand five zero zero,” matching the official example—not “three five zero zero” alone without the field-elevation phrase, and not “thirty-five hundred” in the official table form.

Side-by-side comparison table (study sheet)

Putting it together in a radio exchange

A single ground reply might combine several number types (adapted from RIC-21 message examples):

• Wind one six zero at one five
• Altimeter two niner niner seven
• Frequency one two two decimal one
• Time zero niner two zero zulu

Each fragment follows §5.4. Your job as an ROC-A candidate is to produce those fragments without sliding back into casual “one sixty” or “one twenty-two point one.”

Common exam traps

Official source

RIC-21 Issue 3, section 5.4 Transmission of Numbers, including the worked examples for general numbers, decimals, money, altitude, flight level, group forms, time, headings, and field elevation. Cross-read §5.2 (time structure) and §5.3 (digit pronunciation table) for a complete numbers skill set on the ROC-A exam.