“Pronouncing Numbers and Letters in Aviation Communication”

A detailed discussion of the ICAO phonetic alphabet, rules for pronouncing numbers, altitudes, headings, and radio frequencies. The article includes practical exercises and the most common errors.

1. The ICAO Phonetic Alphabet

To ensure absolute clarity over static-filled radios and across different accents, aviation uses a standardized phonetic system. Standard phraseology reduces misunderstanding caused by:

• accent variation
• radio distortion
• similar-sounding letters

The internationally accepted standard is defined by the International Civil Aviation Organization (ICAO). ICAO Phonetic Alphabet the stressed syllables are in CAPITAL LETTERS

Letter	Word	Pronunciation
A	Alpha	AL fah
B	Bravo	BRAH voh
C	Charlie	CHAR lee or SHARLEE
D	Delta	DELL tah
E	Echo	ECK oh
F	Foxtrot	FOKS trot
G	Golf	GOLF
H	Hotel	ho TELL
I	India	IN dee ah
J	Juliett	JEW lee ETT
K	Kilo	KEY loh
L	Lima	LEE mah
M	Mike	MIKE
N	November	no VEM ber
O	Oscar	OSS cah
P	Papa	pah PAH
Q	Quebec	keh BECK
R	Romeo	ROW me oh
S	Sierra	see AIR rah
T	Tango	TANG go
U	Uniform	YOU nee form or OO nee form
V	Victor	VIK tah
W	Whiskey	WISS key
X	X-ray	X ECKS ray
Y	Yankee	YANG key
Z	Zulu	ZOO loo

Why This Matters

Without standardization there would be a lot of confusion:

• B/P
• M/N
• S/F

These errors have contributed to:

• wrong taxiway entry
• incorrect clearances
• navigation errors

2. Rules for Pronouncing Numbers

ICAO modifies number pronunciation to improve clarity over radio. Standard ICAO Number Pronunciation

Numeral or numeral element	Pronunciation
0	ZE-RO
1	WUN
2	TOO
3	TREE
4	FOW-er (two syllables)
5	FIFE
6	SIX
7	SEV-en
8	AIT
9	NIN-er
Decimal	DAY-SEE-MAL
Hundred	HUN-dred
Thousand	TOU-SAND

Number Confusion

Numbers like “two” and “to” or “ten” and “eleven” are easily confused. Standard pronunciation: Use “tree” for 3, “fife” for 5, “niner” for 9 and “fower” for 4 to maintain phonetic clarity.

Why “Tree”, “Fife”, and “Niner”?

To avoid confusion with:

• Three / Free or Sri – the “th” sound is hard to hear over radio and to avoid mispronunciation and confusion with other words the command to shoot
• Five / Fire
• Nine / Nein German influence historically
• Four / For to distinguish it from the preposition

This improves international intelligibility.

Grouping Rules

Numbers are spoken as individual digits, with specific modifications to avoid confusion. General rule: pronounce digits individually.

• Heading 180 is always three digits
  • One Eight Zero
• 005°: Zero Zero Five degrees
• Aircraft call signs
  • EK 172: Emirates One Seven Two
• Altimeter settings
  • QNH 998: QNH Niner Niner Eight
• Wind direction and speed
  • 100 degrees 15 knots gusting 30: wind One Zero Zero degrees One Five knots gusting Tree Zero
• Runways
  • Runway 27: runway Two Seven
  • With letter Runway 27L: runway Two Seven Left
• Flight levels
  • FL 95: Flight Level Niner Fife
  • FL 120: Flight Level One Two Zero
• Altitudes, Cloud Base, Visibility, Runway Visual Range, Flight Level, Transponder Codes and Altimeter Setting information: when contain whole hundreds or whole thousands are spoken as a word
  • 300 feet: Tree Hundred feet
  • 11,000 feet: One One Thousand feet
• Visibility 1000: visibility One Thousand
• RVR 1700: RVR One Thousand Seven Hundred
• Transponder code 7000: squawk Seven Thousand
• Altimeter 1000: QNH One Thousand
• Flight level FL 100: flight level One Hundred

Specific Categories

Radio Frequencies
The decimal point (.) is spoken as “Decimal.” In some regions, “Point” is used, but ICAO standard is „Decimal.” Never group digits.

• ✅ 118.7: One One Eight Decimal Seven
• ✅ 118.000: One One Eight Decimal Zero
• ✅ 118.010: One One Eight Decimal Zero One Zero
• ✅ 118.100: One One Eight Decimal One
• ✅ 121.075: One Two One Decimal Zero Seven Five
• ❌ X One Eighteen One Hundred
• ❌ “One One Eight Point Seven”

Time
Aviation uses UTC (Zulu) time in a 24-hour format, usually only the minutes are spoken if the hour is obvious.

• 14:05: “Zero Five” or “One Four Zero Five.”

3. Common Errors

• Using “Hundred” or “Ten” for Headings: Saying “Heading two hundred” instead of “Heading two zero zero.” Other examples:
  
  
  
  • ❌ “Ninety”
  
  
  • ❌ “Two seventy”
  
  
  
  

  These are non-standard and reduce clarity.

  
  
• Dropping “Zero”: Saying “Heading 5” instead of “Heading Zero Zero Five.” Leading zeros are mandatory for headings.
• The “To/Two” Conflict: Saying “Climb to five thousand” can sound like “Climb 25,000.” Correction: Use “Climb and maintain five thousand.”
• The “Roger” Reflex: Using “Roger” (I received your transmission) when you should be giving a full readback of data.
• Using other numbers than single digits when mentioning the Flight Level:
  • ❌ “One twenty”
  • ❌ “One hundred and twenty”
  • ❌ “One hundred twenty”

4. Correct Pilot Responses

If the aircraft is at FL150:

“Maintaining flight level one five zero.”
or
“Flight level one five zero.”

If the aircraft is NOT at FL150:

• At FL140:
  
  

  “Negative, maintaining flight level one four zero.”

  
  
• Climbing to FL150:
  
  

  “Climbing to flight level one five zero.”

  
  
• Descending through FL150:
  
  

  “Descending through flight level one five zero.”

  
  

Incorrect/Unsafe Responses

• ❌ “Affirm.”
• ❌ “Confirm.”
• ❌ “Roger.”
• ❌ “Yes.”

⚠️ These do not state the aircraft’s actual level and can lead to loss of separation.

“Confirm flight level one five zero.” — the pilot must state the actual level the aircraft is at or maintaining, not just say “affirm” or “confirm”.

Why ICAO Requires This

“Confirm” from ATC means:

“Tell me exactly what you are doing now.”

The pilot response must therefore:

• include the actual level
• use a clear action verb
• remove all ambiguity

Never confirm a level with yes/no – always confirm with a level. This exact point is frequently tested in:

• ICAO speaking exams
• airline simulator checks
• ATC assessments

5. Practical exercises

“Verify altitude three thousand feet.”

❌ Wrong:

• “Verified.”

✅ Correct:

• “Maintaining three thousand feet.”
• “Descending to three thousand feet.”

Trap: “Verify” means state your current or cleared altitude.

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“Confirm heading two seven zero.”

❌ Wrong:

• “Affirm.”
• “Yes.”

✅ Correct:

• “Heading two seven zero.”
• or “Turning heading two seven zero.”

Trap: ATC is checking where you are currently flying, not asking a yes/no question.

---

“Confirm passing flight level one zero zero.”

❌ Wrong:

• “Yes.”

✅ Correct:

• “Passing flight level one zero zero.”
• or “Maintaining flight level one zero zero.”

Trap: ATC may be checking conflict resolution.

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“Verify crossing altitude five thousand.”

❌ Wrong:

• “Verified.”

✅ Correct:

• “Crossing five thousand feet.”
• or “Unable to cross five thousand due to [Reason/Capability].”

Trap: This checks compliance with restrictions, not awareness.

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“Check speed two one zero knots.”

❌ Wrong:

• “Checked.”

✅ Correct:

• “Speed two one zero knots.”
• or “Reducing speed to two one zero knots.”

Trap: “Check” is a confirmation word. It means say the number.

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Numbers in Correct Readbacks

Pilot:

“Taxi via Bravo, hold short Runway Two Five at Alpha Two, SP-DRE.”

Why this prevents runway incursion: To eliminate any possibility of misunderstanding:

• ☑ Full runway number repeated (“Runway Two Five”)
• ☑ Hold short instruction clearly stated
• ☑ Intersection identified precisely (“Alpha Two”)
• ☑ Call sign placed at the end (standard readback format)

Even more emphasis, if required for safety:
In complex traffic or low visibility, you may add extra precision:

“SP-DRE taxiing via Bravo, will hold short of Runway Two Five at Alpha Two.”

This reinforces:

• ☑ You understood the route
• ☑ You will stop before entering the runway
• ☑ You are aware of the exact holding point

What NOT to say:

• ❌ “Roger”
• ❌ “Taxiing”
• ❌ “Holding short”
• ❌ Omitting runway number
• ❌ Omitting intersection

Incomplete readbacks are a major contributor to runway incursions.

6. More practice

Exercise 1: Spell the Callsign
ABC452
Correct: “Alpha Bravo Charlie four fife too”

Exercise 2: Read the Clearance
“Descend to FL180, contact 121.9”
Correct: “Descending flight level one eight zero, one two one decimal niner”

Exercise 3: Taxi Instruction
“Taxi via A3 to holding point RWY 27”
Correct: “Taxi via Alpha tree to holding point runway two seven”

Exercise 4: Frequency Change
“Contact Tower 119.3”
Correct: “One one niner decimal tree”

7. Things to remember:

Error	Risk
Saying “two forty”	Altitude deviation
Saying “point”	Frequency confusion
Mixing local pronunciation	International misunderstanding
Dropping “flight level”	Level confusion
Not using phonetics	Taxiway errors

8. Human Factors Considerations

Pronunciation errors increase when:

• workload is high
• stress is elevated
• fatigue is present
• strong accent interference occurs

Standard pronunciation reduces cognitive load for both sender and receiver.

9. ICAO Level 4 vs Level 6 Perspective

Level 4

• Mostly correct numbers
• Occasional local accent interference

Level 6

• Fully standard
• No hesitation
• Digit-by-digit consistency
• Clear under pressure

10. Final Safety Principle

Aviation does not tolerate “almost correct” numbers. One mispronounced digit can cause:

• loss of separation
• wrong runway entry
• navigation error

Precision is not formality – it is a barrier against accidents.

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Resources

Manual of Radiotelephony Doc 9432 AN/9 Fourth Edition 2007 International Civil Aviation Organization
APPENDIX 2 DIFFERENCES FROM ICAO RADIOTELEPHONY PROCEDURES