FAR 21.129 — Propeller Functional Tests
FAR 21.129 requires manufacturers of variable pitch propellers under a type certificate to perform a functional test across the normal operating range.
FAR 21.129 sets a manufacturing quality requirement for propellers built under a type certificate. It applies specifically to variable pitch propellers — the kind whose blade angle changes during operation (constant-speed and controllable-pitch propellers).
The rule requires the manufacturer to:
- Perform an acceptable functional test on each variable pitch propeller produced.
- Verify that the propeller operates properly throughout the normal range of operation.
In other words, every individual variable pitch propeller leaving the factory must be exercised and confirmed to work correctly across its full operating envelope, not just spot-checked or sampled.
Why it matters operationally: As a pilot, you rely on your propeller smoothly changing pitch in response to throttle and prop control inputs — for takeoff, climb, cruise, and descent. This regulation is part of the safety chain that ensures the propeller you're using has been individually tested before installation, reducing the risk of in-flight pitch control failures.