Definition
A complete sequence of events that returns to its starting condition, ready to repeat. In aviation, the term most commonly refers to one full operational use of a component — for example, a single landing-gear extension and retraction, or one engine start-and-shutdown — used as a unit for tracking service life and maintenance intervals.
Plain English
One full round of an action, from start, through the action, and back to where it began. Many aircraft parts wear out based on how many times they're used (cycles), not just how many hours they've been running.
Context Anchor
Seen in engine, electrical, systems, and maintenance discussions when describing something that repeats in a set pattern.
Derivation
From the Greek 'kyklos,' meaning 'circle' or 'wheel.' The idea is of something coming back around to where it started — useful in aviation because many components are tracked by how many times they complete a full operating round, not just elapsed time.
Why Pilots Care
Some life-limited parts are retired based on cycles rather than flight hours. A short flight and a long flight each count as one cycle for the landing gear or engine, so a heavily used trainer aircraft can reach cycle limits faster than its hours alone would suggest.
Analogy
A washing machine cycle is one full run from start to finish. An aviation cycle is the same idea: one complete run through a repeating process.
Intuition Check
Do not read cycle as just “a period of time” or as something vague that happens repeatedly. In this context, it means one complete sequence from start, through all required steps, and back to a ready-to-repeat point.
Example Sentence 1
The landing gear actuator is life-limited to 20,000 cycles, so the maintenance team logs every extension and retraction.
Example Sentence 2
Mechanics record each engine cycle in the logbook to schedule the next inspection.