Definition
The circular area swept by the rotating blades of a propeller. This area is treated as a hazard zone because a turning propeller is nearly invisible and can cause severe injury or death to anyone who enters it.
Plain English
The invisible circle that the spinning propeller blades carve out in the air. Anything inside that circle while the prop is turning will be struck.
Context Anchor
Used in hand-propping procedures and ramp safety discussions, especially when someone is near the front of the airplane.
Derivation
Arc comes from the Latin arcus, meaning bow or curved shape. The spinning blade tips trace a circle, and any slice of that circle is an arc — so the whole swept disc is called the propeller arc.
Why Pilots Care
Anyone standing inside the propeller arc risks serious injury or death if the engine starts unexpectedly during hand propping.
Intuition Check
Do not think of the propeller arc as only the visible blade position when the propeller is stopped. It means the whole circular path the blades can sweep through once the propeller moves.
Example Sentence 1
Before starting the engine, the pilot checked that no one was standing within the propeller arc.
Example Sentence 2
The safety briefing emphasized staying outside the propeller arc until the engine was running and the pilot was seated at the controls.