Definition
A mechanical limit built into a constant-speed propeller that prevents the blades from rotating to a blade angle below a set minimum. It defines the flattest pitch the propeller can assume during normal operation and marks the lower boundary of the propeller governing range.
Plain English
It's a built-in stop inside the propeller that keeps the blades from flattening out past a certain angle. The blades can twist to take bigger or smaller bites of air, but they can't flatten beyond this point.
Context Anchor
Seen in discussions of constant-speed propellers and governing range, especially when explaining why the propeller can hold a selected RPM only between its blade-angle limits.
Derivation
Pitch' here refers to the blade angle of the propeller — how steeply the blades are twisted into the air. 'Low pitch' means a flat blade angle (small bite of air, which allows higher RPM). The 'stop' is a physical limit. So 'low pitch stop' literally means 'the limit that prevents the blades from going any flatter.'
Why Pilots Care
Keeps the propeller from overspeeding and damaging the engine if oil pressure to the governor is lost.
Intuition Check
Do not read pitch here as airplane nose attitude. In this term, pitch means propeller blade angle. Do not read stop as stopping the propeller. It means a mechanical limit that prevents further blade movement.
Example Sentence 1
At idle on the ground, the propeller is sitting against the low pitch stop, so the governor isn't actively controlling RPM.
Example Sentence 2
If the propeller governor fails, the blades move all the way to the low pitch stop and RPM rises sharply.