Definition
A one-way mechanical clutch that transmits torque in one direction of rotation only. When the driven member begins to rotate faster than the driving member, the clutch automatically disengages and allows the driven member to spin freely without back-driving the drive system.
Plain English
A connector between two rotating parts that grips when one part is driving the other, but lets go the moment the driven part starts spinning faster on its own. It only pulls in one direction.
Context Anchor
Seen in aircraft engine starting-system descriptions and maintenance discussions of starter drive assemblies.
Derivation
From 'overrun' — to run past or faster than something. The clutch allows the driven side to 'over-run' the driving side without dragging it along. The name describes exactly what it does mechanically.
Why Pilots Care
Protects the starter motor from being driven at high engine speeds after start, preventing mechanical failure.
Analogy
Like the freewheel on a bicycle. You pedal forward and the wheel turns. Stop pedaling and the wheel keeps going on its own — your pedals don't get yanked around with it.
Intuition Check
“Overrunning” here is not about an aircraft going past a runway or limit. It means the engine has started turning faster than the starter, so the clutch releases.
Example Sentence 1
Once the engine started and accelerated, the overrunning clutch released the starter so it would not be driven by the engine.
Example Sentence 2
Mechanics inspect the overrunning clutch during engine overhaul to ensure it still allows free rotation in the overrun direction.