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.
The short answer
This AIM section is FAA advisory guidance on stating time in radio and telephone communications. It explains that the FAA uses Coordinated Universal Time (UTC), denoted "Zulu," requires "local" when local time is given, and uses the 24-hour clock with current time stated to the nearest quarter minute, supporting standardized Part 91 ATC phraseology.
Research Notes
Common Questions
How do I convert my local standard time to UTC?
Per TBL 4-2-3, add 5 hours for Eastern, 6 for Central, 7 for Mountain, 8 for Pacific, 9 for Alaska, and 10 for Hawaii Standard Time. For daylight time, subtract 1 hour.
What does "Zulu" mean on the radio?
The term "Zulu" may be used to denote UTC. The FAA uses Coordinated Universal Time for all operations; when local time is given, the word "local" or the time zone equivalent must be used—for example, 0920 UTC is spoken "zero niner two zero."
How precisely is the current time given for a time check?
Current time in use at a station is stated in the nearest quarter minute. Fractions of a quarter minute less than 8 seconds are stated as the preceding quarter minute; 8 seconds or more as the succeeding quarter minute—so 0929:10 becomes "zero niner two niner and one-quarter."