Definition 1 of 2
Definition
An installed cockpit timepiece displaying hours, minutes, and seconds, used by the pilot to time flight events such as instrument approach segments, holding pattern legs, fuel burn intervals, and dead-reckoning navigation. For helicopter instrument flight under Part 91, a clock displaying hours, minutes, and seconds with a sweep-second pointer or digital presentation is required equipment.
Plain English
A timing device fitted in the cockpit that shows hours, minutes, and seconds, so the pilot can accurately time things like approach legs and holding turns.
Context Anchor
Seen in aircraft equipment lists and used during instrument flying, especially when a procedure or clearance requires accurate timing.
Derivation
Clock comes from an old word for a bell, because early clocks marked time by ringing. The useful idea for aviation is not the bell, but a dependable device that marks time clearly.
Why Pilots Care
Allows rapid, unambiguous communication of relative bearings during instrument flight when visual references are limited.
Intuition Check
Do not read “clock” here as just any casual time display. In this context, it means a usable aircraft time source that shows hours, minutes, and seconds clearly enough for flight timing.
Example Sentence 1
Crossing the final approach fix, the pilot started the clock to time the descent to the missed approach point.
Example Sentence 2
Scan the nine o'clock position for any rising terrain during the approach.