Definition
FOD (Foreign Object Debris) refers to any loose object on a ramp, taxiway, runway, or in/around an aircraft that does not belong there and could be ingested by an engine, struck by a propeller, damage tires, or be blown into people or other aircraft by prop or jet blast. The same acronym is also used for Foreign Object Damage, meaning the harm caused when such debris contacts an aircraft, engine, or propeller.
Plain English
Any loose item — rocks, bolts, tools, fuel caps, trash, gravel — that shouldn't be on the ramp or runway and could damage an aircraft if sucked into an engine, hit by a prop, or thrown around by the wind from one.
Context Anchor
Seen in aircraft systems discussions about propellers and in ramp, runway, taxiway, and preflight safety discussions about keeping loose objects away from aircraft.
Derivation
Foreign means 'not belonging here,' object means 'a physical thing,' and debris (from French débris, 'broken-down remains') means 'loose bits and pieces.' Put together: stuff that doesn't belong on an airport surface.
Why Pilots Care
Choosing the correct fixed-pitch design affects takeoff distance, climb rate, and cruise speed; a climb propeller sacrifices some cruise efficiency for better low-speed performance.
Intuition Check
Do not read this as one normal phrase. It is best understood as two separate glossary items: fixed-pitch propellers and FOD. Also, pitch here means blade angle, not sound.
Example Sentence 1
Before starting the engine, the pilot walked the area around the propeller arc and picked up a small bolt to prevent FOD.
Example Sentence 2
After takeoff the pilot monitors engine RPM knowing the fixed-pitch propeller cannot be adjusted for the cruise portion of the flight.