Definition
On a propeller-driven airplane, the act of rotating the propeller blades on a failed or shut-down engine until they are aligned edge-on to the relative wind, so the propeller stops turning and produces minimum drag.
Plain English
Turning the blades of a stopped engine's propeller so their thin edges face forward into the airflow. This stops the propeller from spinning and dramatically reduces the drag it would otherwise create.
Context Anchor
Encountered in multiengine airplane training and emergency checklists, especially after an engine failure.
Derivation
From the older nautical and aeronautical use of 'feather,' meaning to turn an oar or blade so it slices edgewise through air or water. The blade then resembles a feather lying flat against the airflow rather than catching it.
Why Pilots Care
Eliminates the heavy drag of a windmilling propeller, allowing the aircraft to maintain better speed and control on the remaining engine.
Analogy
It is like turning a paddle edgewise in moving water. Held flat, it resists the flow; turned edgewise, it slips through with much less force.
Intuition Check
Do not read “full” as maximum power or maximum thrust here. In full feathering, the propeller is set to minimize drag, not to pull the airplane forward.
Example Sentence 1
After confirming the right engine had failed, the pilot moved the propeller control to the full feathering position to reduce drag.
Example Sentence 2
In training the instructor had the student practice full feathering on the simulated failed engine to keep the airplane flying cleanly.