Definition
The act of rotating the blades of a controllable-pitch propeller until they are aligned with the direction of flight, presenting their thinnest edge to the airstream. Feathering stops the propeller from windmilling on a shut-down or failed engine, dramatically reducing drag and the bending loads on the engine and airframe.
Plain English
Turning the propeller blades edge-on to the wind so they slice through the air instead of catching it. This stops the prop from spinning when the engine is off and keeps the airplane from being dragged sideways by a dead engine.
Context Anchor
Seen in propeller system discussions, multi-engine engine-out procedures, and helicopter rotor blade descriptions.
Derivation
From the old image of a bird's feather lying flat against the wind. A feather aligned with the airflow offers almost no resistance, which is exactly what a feathered blade does in flight.
Why Pilots Care
Greatly reduces asymmetric drag, improves single-engine climb performance, and prevents further damage to a failed engine.
Intuition Check
Feathering does not mean the blade becomes lighter or grows feathers. It means the blade is twisted to a different angle, usually to reduce air resistance or change how the blade works in the airflow.
Example Sentence 1
After confirming the right engine had failed, the pilot pulled the propeller control aft to feather the blades and reduce drag.
Example Sentence 2
With both blades feathered, the airplane could maintain altitude on the remaining engine.