Time, UTC and Date-Time Groups

Aviation needs one shared clock

Local civil time is useful on the ground, but aviation information needs a common reference. Weather, NOTAMs and operational coordination use Universal Coordinated Time, normally written as UTC.

A four figure group gives the hour and minutes on the 24 hour clock. For example, 0525 means 5:25 am UTC, while 1525 means 3:25 pm UTC.

Australian conversions need the date as well as the hour

Eastern Standard Time is 10 hours ahead of UTC. To convert EST to UTC, subtract 10 hours. If that takes you before midnight, the UTC time is on the previous date.

The trap is assuming the date remains unchanged. A NOTAM or weather validity time near midnight can belong to yesterday or tomorrow in local time.

• Four figures usually mean hour and minute.
• Six figures usually mean day, hour and minute.
• Eight or ten figures can add month and year when the wider date context is needed.

Use date-time groups operationally

Remote pilots should be comfortable turning local job times into UTC for flight planning and reading UTC information back into local time for the crew.

When the operation depends on a NOTAM, forecast window or approval time, write the local and UTC interpretation in the job pack. That small habit prevents avoidable timing errors.

Practice Questions