Definition
The unintended escape of fuel from any part of the airplane's fuel system, including tanks, lines, fittings, drains, vents, fuel caps, or the engine fuel system. Leakage may appear as visible drips, wet stains, blue dye streaks on the airframe, or a persistent fuel odor.
Plain English
Fuel coming out of the airplane somewhere it shouldn't — through a loose fitting, a damaged line, a worn seal, or a tank that isn't sealed properly.
Context Anchor
Seen during preflight inspection, especially when checking fuel tanks, caps, drains, the underside of the wing or fuselage, and the engine area.
Why Pilots Care
Fuel leakage creates an immediate fire hazard, risks fuel starvation in flight, and indicates a system problem that must be corrected before takeoff.
Intuition Check
Do not assume fuel leakage only means a large, obvious stream of fuel. A stain, drip, wet spot, or fuel smell can also point to fuel escaping where it should not.
Example Sentence 1
During preflight, the pilot noticed a blue stain under the left wing fuel cap and grounded the airplane until a mechanic could check the fuel leakage.
Example Sentence 2
After landing, the mechanic inspected the fuel lines for any new signs of leakage.