Definition
The act of rotating the blades of a variable-pitch propeller so that their leading edges align nearly parallel to the oncoming airstream, presenting the thinnest possible profile to the relative wind. Feathering stops the propeller from rotating (or reduces its rotation to a minimum) and dramatically reduces aerodynamic drag from a failed or shut-down engine. It is used primarily on multi-engine airplanes after an engine failure, and on some single-engine turboprops during shutdown.
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 and removes the heavy drag that a stopped or windmilling prop would otherwise create.
Context Anchor
Used in multi-engine and turbine airplane procedures, especially during engine shutdown, engine failure, and securing a failed engine.
Derivation
From 'feather,' as in the way a rower 'feathers' an oar -- turning the blade flat and parallel to the water on the return stroke so it slips through with minimal resistance. Same idea here: turn the blade edge-on to the airflow so it stops grabbing air.
Why Pilots Care
Feathering a failed engine’s propeller cuts drag dramatically, improving climb performance, airspeed control, and the chance of reaching a safe landing site.
Analogy
Like turning a hand-held paddle sideways in a flowing stream. Held flat against the current, it pushes hard on your arm. Turned edge-on, the water slips past with almost no resistance.
Intuition Check
Propeller feathering does not mean adding feathers, smoothing the propeller, or simply stopping it. It means changing the blade angle so the stopped or failed propeller creates much less drag.
Example Sentence 1
After confirming the right engine had failed, the pilot moved the propeller control to the feather position to reduce drag and maintain altitude on the remaining engine.
Example Sentence 2
The checklist called for the student to identify the failed engine, verify, and then feather the propeller before securing the engine.