Definition
Spring-loaded pins inside a feathering propeller hub that mechanically prevent the propeller blades from drifting into the feathered position when the engine is shut down on the ground. They are held disengaged in flight by centrifugal force acting on the pins as the propeller rotates above a set RPM, and they re-engage to lock the blades out of feather as RPM falls below that threshold during shutdown.
Plain English
Small internal pins that stop the propeller blades from turning edge-on to the wind on their own when the engine is shut off on the ground. They lock automatically when the prop slows down and release automatically once it spins fast enough.
Context Anchor
Seen in multiengine airplane propeller systems, especially during discussions of engine shutdown, feathering checks, and propeller operation at low engine speed.
Derivation
Feathering' comes from turning the propeller blades so their edges face the wind, like the feather of an arrow aligned with airflow. 'Anti-' simply means 'against' or 'preventing.' So anti-feathering lock pins are pins that prevent feathering -- specifically, prevent it from happening when it shouldn't.
Why Pilots Care
They stop the propeller from feathering accidentally during takeoff, climb, or normal flight, which would suddenly reduce thrust and create control problems.
Grounding Statement
At low engine speed, the pins hold the blades out of feather; at higher engine speed, the pins release and feathering becomes available.
Intuition Check
Do not read “anti-feathering” as meaning the propeller can never feather. These pins only prevent feathering while the engine speed is low enough for the locks to stay engaged.
Example Sentence 1
When the engine is shut down on the ground, the anti-feathering lock pins engage and hold the blades at a low pitch so the propeller doesn't drift into feather.
Example Sentence 2
During the preflight inspection the pilot confirmed the anti-feathering lock pins were engaged to prevent any blade movement on the ground.