Definition
The short tubular opening on a fuel or oil tank through which the tank is filled. The filler neck typically extends a small distance down into the tank and is closed by a removable cap. In fuel tanks, the bottom of the filler neck often serves as a built-in marker for maximum usable fuel, since fuel above that level can spill out as the aircraft moves or the fuel expands.
Plain English
The opening you pour fuel or oil into on a tank, with a cap on top to seal it.
Context Anchor
Seen during preflight inspection, fueling, oil servicing, and maintenance checks of aircraft tanks or reservoirs.
Derivation
“Filler” comes from “fill,” meaning to make something full. “Neck” is used like the narrow neck of a bottle. Together, the term points to the narrow opening used to fill a tank.
Why Pilots Care
Allows safe fuel addition while reducing spill hazards and letting pilots inspect for contamination before flight.
Analogy
It is like the opening behind a car’s fuel door: the cap comes off, and the neck is the fixed passage the fuel goes through into the tank.
Intuition Check
Do not confuse the filler neck with the filler cap. The neck is the fixed opening on the tank; the cap is the removable cover that closes it.
Example Sentence 1
During preflight, the pilot removed the fuel cap and confirmed the fuel was level with the bottom of the filler neck.
Example Sentence 2
After adding fuel, the line person wiped the filler neck clean to avoid attracting dirt or water.