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.
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.
Five FAA-written-style questions. Instant explanations, every answer cites its source — no account needed.
You are flying VFR in Class E airspace at 8,500 feet MSL during the day. What are your minimum visibility and cloud clearance requirements?