Definition
The opening on an aircraft fuel tank through which fuel is added during refueling. It is fitted with a removable cap and is marked with the approved fuel grade and minimum fuel rating for that aircraft.
Plain English
The hole on top of the fuel tank where fuel goes in. It has a cap, and the correct fuel type is marked next to it.
Context Anchor
Seen during preflight inspection, refueling, and fuel system descriptions in the aircraft handbook.
Why Pilots Care
A properly secured filler opening prevents water, dirt, and debris from entering the fuel system, reducing the risk of engine failure.
Intuition Check
Do not think of “filler” as the person adding fuel. Here, “filler opening” means the aircraft’s fuel-fill point—the place where fuel is put into the tank.
Example Sentence 1
During preflight, the pilot opened the filler opening on the left wing to visually check the fuel quantity.
Example Sentence 2
After refueling, the cap on the filler opening was checked to ensure it locked securely.