FAA Commercial Pilot Airplane (CAX)Aircraft SystemsMedium
A twin-engine airplane's propeller system includes a small cylinder that stores engine oil under pressure specifically to allow a feathered propeller to be unfeathered and restarted in flight. What is this component called?
- AFeathering pump relief valve
- BGovernor pilot valve
- COil separator tank
- DUnfeathering accumulator
Show answer & explanationAnswer & explanation
Correct answer: D. Unfeathering accumulator
An unfeathering accumulator stores pressurized oil that, when released, drives the propeller blades out of the feathered position so the engine can be restarted and the governor can resume normal control. Without it, an engine-driven oil pump alone (stopped with the engine) could not move the blades quickly.
Why the other options are wrong
- A. There is no standard 'feathering pump relief valve' component described this way.
- B. The governor pilot valve directs oil flow but does not store a reserve charge for unfeathering.
- C. An oil separator removes oil from air/gas streams, unrelated to propeller feathering.
Unfeathering Accumulator
A device that stores oil under pressure so a feathered propeller can be moved out of feather and the engine restarted in flight.
- Found on multiengine feathering propeller systems
- Provides initial oil charge before engine-driven pump resumes
- Essential because a stopped engine's oil pump can't feather/unfeather alone
Memory trick: Stored oil punch gets a feathered blade back to work.