Definition
A spring-loaded locking finger that engages the notches or lobes of a cam to permit movement in one direction while preventing movement in the opposite direction. Cam pawls are commonly found in mechanisms such as one-way clutches, ratchets, and certain starter and override drives in aircraft engines and accessories.
Plain English
A small, spring-loaded catch that drops into a notch on a rotating part so the part can turn one way but not the other.
Context Anchor
Seen in piston-engine ignition system maintenance, especially when inspecting or troubleshooting a magneto impulse coupling.
Derivation
‘Cam’ comes from a Dutch word meaning a projecting part on a wheel that gives motion to another part. ‘Pawl’ comes from an old word for a pivoted bar or finger that catches into teeth or notches. Together the term describes a small finger (pawl) that engages with the lobes or notches of a cam.
Why Pilots Care
A worn or broken cam pawl can prevent starter engagement, leading to failed engine starts or damage to the starter drive.
Analogy
Like the catch inside a socket wrench: turn it one way and it grips and drives; turn it the other way and it slips freely.
Example Sentence 1
The mechanic replaced the worn cam pawl in the starter clutch after the engine failed to crank reliably.
Example Sentence 2
A faulty cam pawl prevented the starter from turning the engine over even though the motor spun freely.