Definition
A timekeeping system that numbers the hours of the day from 00 through 23, with no AM or PM. Midnight is 0000, noon is 1200, and one minute before the next midnight is 2359. Used in aviation for all official times to remove any ambiguity about morning or afternoon.
Plain English
A way of writing the time using numbers from 0000 to 2359 instead of splitting the day into two halves. Once you pass noon, you keep counting upward — 1300 is 1 PM, 1400 is 2 PM, and so on, all the way to 2359, which is one minute before midnight.
Context Anchor
Seen in time zone discussions, flight planning, weather reports, log entries, and any aviation situation where a time must be stated without a.m./p.m. confusion.
Why Pilots Care
Eliminates any possibility of confusing morning and evening times during flight planning and radio calls.
Grounding Statement
A time like 1730 means 5:30 p.m.; the hour 17 tells you it is after noon without needing the letters p.m.
Intuition Check
Do not read “24-hour clock” as a clock that runs for only 24 hours. It means a way of writing time that counts the hours of the day from 00 through 23 instead of using a.m. and p.m.
Example Sentence 1
The pilot filed a flight plan with a departure time of 1430.
Example Sentence 2
The METAR showed the next update would be issued at 0815Z.