Definition
To return the blades of a feathered propeller from their streamlined, edge-into-the-wind position back to a normal pitch range so the propeller can again produce thrust. Unfeathering is performed during an in-flight engine restart on a multi-engine aircraft, and is typically accomplished by an unfeathering accumulator, an electric pump, or by windmilling the propeller in the airstream.
Plain English
To rotate a stopped, streamlined propeller back to a working angle so the engine can be restarted and the propeller can pull the airplane forward again.
Context Anchor
Used in multi-engine propeller aircraft, especially during an engine restart after a propeller has been feathered.
Derivation
The prefix 'un-' means to reverse an action. 'Feather' in aviation refers to turning propeller blades edge-on to the airflow. So 'unfeather' literally means to undo the feathering — bring the blades back out of that streamlined position.
Why Pilots Care
Enables an in-flight engine restart or restores normal propeller operation after feathering an engine.
Intuition Check
Unfeather does not mean simply restarting the engine. It specifically means moving the propeller blades out of the feathered position.
Example Sentence 1
After securing a successful airstart on the right engine, the pilot used the unfeathering accumulator to bring the propeller back into the governing range.
Example Sentence 2
After clearing the engine problem, the crew unfeathered the left propeller and verified oil pressure.