AIM Text
- Up to but not including 18,000 feet MSL, state the separate digits of the thousands plus the hundreds if appropriate.
- At and above 18,000 feet MSL (FL 180), state the words “flight level” followed by the separate digits of the flight level.
Source: FAA Aeronautical Information Manual · current edition · paragraph 4-2-9.
The short answer
This AIM section is FAA advisory phraseology guidance for speaking altitudes and flight levels on the radio. Up to but not including 18,000 feet MSL, state the separate thousands digits plus hundreds if appropriate; at and above 18,000 feet MSL (FL 180), say “flight level” followed by the separate digits. It supports clear communication under 14 CFR 91.183.
Research Notes
Common Questions
How do you say 12,500 feet over the radio?
Below 18,000 feet MSL, state the separate thousands digits plus the hundreds if appropriate. AIM 4-2-9 shows 12,500 spoken as “one two thousand five hundred” and 12,000 as “one two thousand.”
When do you start using the term “flight level”?
At and above 18,000 feet MSL (FL 180), per AIM 4-2-9. You state the words “flight level” followed by the separate digits — for example, FL 190 is “Flight Level One Niner Zero.”
How is a flight level like 275 spoken?
As separate digits after “flight level.” AIM 4-2-9 gives FL 275 as “Flight Level Two Seven Five.” This is advisory phraseology guidance.