AIM Text
- FAA uses Coordinated Universal Time (UTC) for all operations. The word “local” or the time zone equivalent must be used to denote local when local time is given during radio and telephone communications. The term “Zulu” may be used to denote UTC.
- To convert from Standard Time to Coordinated Universal Time:
TBL 4-2-3
Standard Time to Coordinated Universal TimeEastern Standard Time Central Standard Time
Mountain Standard Time
Pacific Standard Time
Alaska Standard Time
Hawaii Standard TimeAdd 5 hours
Add 6 hours
Add 7 hours
Add 8 hours
Add 9 hours
Add 10 hours
- A reference may be made to local daylight or standard time utilizing the 24-hour clock system. The hour is indicated by the first two figures and the minutes by the last two figures.
- Time may be stated in minutes only (two figures) in radiotelephone communications when no misunderstanding is likely to occur.
- Current time in use at a station is stated in the nearest quarter minute in order that pilots may use this information for time checks. Fractions of a quarter minute less than 8 seconds are stated as the preceding quarter minute; fractions of a quarter minute of 8 seconds or more are stated as the succeeding quarter minute.
Source: FAA Aeronautical Information Manual · current edition · paragraph 4-2-12.
Research Notes
AIM 4-2-12 covers altitudes and flight levels in ATC communications.
Below 18,000 MSL — altitudes:
- State as "thousand" with the leading digits: "three thousand," "five thousand five hundred," "twelve thousand"
- Some controllers prefer digit-by-digit for non-round altitudes: "five-five hundred" for 5,500
At and above 18,000 MSL — flight levels:
- Prefix with "Flight Level" and state digit-by-digit
- FL180 → "Flight Level one-eight-zero"
- FL410 → "Flight Level four-one-zero"
Altimeter setting transitions: Climbing through 18,000 MSL: reset altimeter to 29.92. Descending through 18,000 MSL: reset to local altimeter setting per § 91.121. This is also where the language switches between "altitude" and "Flight Level."
Standard altitude assignments: ATC assigns altitudes to the foot below FL180 (e.g., "7,500"). At and above FL180, only standard flight levels (multiples of 1,000 below FL290 in RVSM territory; multiples of 1,000 in RVSM airspace; multiples of 2,000 in non-RVSM above FL290).
Reference: § 91.121 (altimeter settings); § 91.179 (IFR cruising altitudes); § 91.180 (RVSM); AIM 4-2-12.