Definition
Physical features fitted to an aircraft's fuel filler port and to fuel nozzles that prevent the wrong type of fuel from being introduced into the aircraft. On piston aircraft, the filler opening is sized so that the larger jet fuel nozzle will not fit, blocking accidental fuelling with jet fuel.
Plain English
Built-in size and shape differences between fuel ports and fuel nozzles that physically stop someone from putting jet fuel into a piston aircraft, or vice versa.
Context Anchor
Seen in preventive maintenance discussions, aircraft fueling procedures, and inspections of the fuel filler openings.
Derivation
‘Misfueling’ combines ‘mis-’ (wrong) with ‘fueling.’ The devices are ‘anti-’ (against) misfueling — physical safeguards against putting in the wrong fuel.
Why Pilots Care
Putting the wrong fuel in an engine can cause immediate failure or long-term damage; these devices block that error at the source.
Grounding Statement
If the wrong fuel nozzle will not fit into the tank opening, the chance of putting the wrong fuel in that tank is greatly reduced.
Intuition Check
Anti-misfueling devices do not make bad fuel safe or remove water or dirt from fuel. They are physical barriers that help prevent the wrong fuel from being added in the first place.
Example Sentence 1
During preflight, the pilot confirmed the anti-misfueling device on the filler port was intact and undamaged.
Example Sentence 2
Anti-misfueling devices on the filler neck stopped the jet-fuel nozzle from fitting during the preflight refuel.