Because aeroplanes are continually moving from one time zone to another, it is the internationally accepted practice in aviation to use a specific time reference known as coordinated universal time (abbreviated UTC) for all expressions of time in radio transmissions and on flight plans, etc UTC is based on longitude 00, which passes through Greenwich, near London. This is the same as Greenwich mean time (GMT). The code letter for this time zone is Z (Zulu). You will hear the same time stated as Zulu and abbreviated to Z.
transmitting time, it is usual only to say the minutes of the hour.
However, if there is any possibility of a misunderstanding or if your ETA is after the next o'clock, then the hour in UTC should also be included.
The subject of time is treated in more detail in our Basic Aeronautical Knowledge and Meteorology and Navigation, and a brief summary is all that we require here.
In aviation, we use the 24-hour clock, the day beginning at 0000 and ending 24 hours later at 2400 (which is of course 0000 for the next day). For example:
- 8:30 in the morning is 0830.
- Midday (12 noon) is 1200.
- One hour later, 1 pm, is 1300 (i.e. 1200 plus 1 hour).
- 4:30 in the afternoon is 1630 (i.e. 1200 plus 0430).
- 8 pm is 2000 (i.e. 1200 plus 0800).
- 8:17 pm is 2017.
| Time | Transmitted as |
|---|---|
| 0815 | WUN FIFE (or ZE-RO AIT WUN FIFE) |
| 1720 | TOO ZE-RO (or WUN SEV-en TOO ZE-RO) |
| 2300 | TOO TREE ZE-RO ZE-RO |
| 0400 | ZE-RO FOW-er ZE-RO ZE-RO |
Relationship of Standard Times to UTC
To convert standard time to coordinated universal time:
UTC = EST minus 10 hours or ESuT minus 11 hours;
UTC = CST minus 9 hours 30 minutes or CSuT minus 10 hours 30 minutes; and UTC = WST minus 8 hours.
Note. Western Australia does not have Summer Time (daylight saving).
For example:
1500 EST = 0500 UTC; and
1600 ESuT = 0500 UTC.
