Definition
The ratio of time a component or system is actively operating to the total time of one complete on-and-off cycle, usually expressed as a percentage or as a maximum allowable on-time followed by a required rest period. Duty cycle limits prevent overheating and damage in equipment that is not designed for continuous operation.
Plain English
How long a piece of equipment is allowed to run before it needs a break. If something has a short duty cycle, you can only use it for a short time, then must let it cool down before using it again.
Context Anchor
Seen in aircraft maintenance and operating limits for parts that are not meant to run continuously, such as starter motors and some electrical equipment.
Derivation
From 'duty' (the work assigned) and 'cycle' (one complete repeating sequence). Together: the share of each repeating period that the equipment is actually on duty doing work.
Why Pilots Care
Knowing the limit prevents overheating and damage to the starter or other components during engine starting or system checks.
Analogy
It is like using a household blender in short bursts. If the instructions say to run it for 30 seconds and then let it rest, that work-and-rest pattern is its duty cycle.
Intuition Check
Duty cycle does not mean a maintenance schedule or a job assignment. Here, it means the repeated pattern of how long a part is on and how long it is off.
Example Sentence 1
The starter has a duty cycle of 30 seconds on, 60 seconds off, with a longer cool-down required after three attempts.
Example Sentence 2
Maintenance instructions require a two-minute cooling period after each duty cycle of the starter motor.