FAA Aviation Mechanic Powerplant (AMP)PropellersMedium
During a run-up, a constant-speed propeller momentarily exceeds its selected RPM setting. How does the governor respond to correct this overspeed condition?
- AThe governor locks the pilot valve in a neutral position, freezing blade angle
- BThe governor increases oil pressure to the propeller hub, allowing blade angle to decrease
- CThe governor shuts off oil flow entirely to feather the propeller
- DThe governor decreases oil pressure to the propeller hub, allowing blade angle to increase
Show answer & explanationAnswer & explanation
Correct answer: D. The governor decreases oil pressure to the propeller hub, allowing blade angle to increase
In an overspeed condition, the flyweights move outward due to excess RPM, moving the pilot valve to drain oil from the propeller hub; this allows the counterweights or springs to increase blade angle, which reduces RPM back to the set value.
Why the other options are wrong
- A. On-speed condition holds the pilot valve neutral, not overspeed.
- B. This describes the response to an underspeed condition, not overspeed.
- C. Feathering only occurs when deliberately commanded, not during normal overspeed correction.
Governor Overspeed Correction
When RPM exceeds the set value, the governor drains oil from the propeller hub, allowing blade angle to increase and RPM to decrease.
- Overspeed: oil drains, blade angle increases
- Underspeed: oil increases, blade angle decreases
- On-speed: pilot valve neutral, no oil flow change
Memory trick: Over means Out (oil out, blade opens up)