AIM ¶ 4-2-9 — Altitude Radio Phraseology
AIM 4-2-9 explains how pilots state altitudes below 18,000 MSL and flight levels at FL180 and above on ATC radio communications. Examples included.
In Plain English
AIM 4-2-9 standardizes how you say altitudes and flight levels on the radio so ATC and other pilots hear them the same way every time. Getting this right helps prevent altitude deviations and readback/hearback errors.
- Below 18,000 feet MSL: State the separate digits of the thousands, plus the hundreds if applicable.
- 12,000 → "one two thousand"
- 12,500 → "one two thousand five hundred"
- At and above 18,000 feet MSL (FL 180): Say the words "flight level" followed by the separate digits.
- FL 190 → "flight level one niner zero"
- FL 275 → "flight level two seven five"
Notice that thousands are spoken digit-by-digit ("one two thousand," not "twelve thousand"), and flight levels never use the word "thousand." This is a recommended phraseology in the AIM rather than a FAR, but examiners and controllers expect it on every readback and altitude report.
AIM Source Text
FAA AIM ¶ 4-2-94-2-9. 4-2-9. Altitudes and Flight Levels
Up to but not including 18,000 feet MSL, state the separate digits of the thousands plus the hundreds if appropriate. EXAMPLE- 12,000 one two thousand 12,500 one two thousand five hundred At and above 18,000 feet MSL (FL 180), state the words “flight level” followed by the separate digits of the flight level. EXAMPLE- 190 Flight Level One Niner Zero 275 Flight Level Two Seven Five
Oral Exam Questions a DPE Might Ask
Q1How do you state an altitude of 12,500 feet MSL on the radio?
Per AIM 4-2-9, below 18,000 MSL state the separate digits of the thousands plus the hundreds: "one two thousand five hundred."
Q2How is FL 275 verbalized to ATC?
Per AIM 4-2-9, at and above 18,000 MSL you say the words "flight level" followed by the separate digits: "flight level two seven five."
Q3At what altitude does phraseology change from stating thousands to stating flight level?
Per AIM 4-2-9, the change occurs at 18,000 feet MSL (FL 180); at and above that altitude you use "flight level" followed by the separate digits.
Related Paragraphs in AIM Chapter 4