A pilot reports a momentary loss of engine power during a steep, uncoordinated turn in a light aircraft that was operating with low fuel quantity in one wing tank. A mechanic investigating the report determines that the fuel tank outlet was momentarily 'unported.' What does this mean?
- AThe electric boost pump lost electrical power during the maneuver
- BFuel in the tank shifted away from the outlet due to the maneuver, momentarily uncovering the pickup and allowing air into the fuel line
- CCarburetor ice formed rapidly during the descending turn
- DThe fuel selector valve was inadvertently moved to the OFF position
Show answer & explanationAnswer & explanation
Correct answer: B. Fuel in the tank shifted away from the outlet due to the maneuver, momentarily uncovering the pickup and allowing air into the fuel line
When fuel quantity in a tank is low, aggressive maneuvering (such as steep, uncoordinated turns) can cause the fuel to slosh away from the tank outlet, momentarily exposing the pickup to air rather than fuel. This is called 'unporting' and results in a temporary interruption of fuel flow and power loss, even though the fuel system itself is functioning normally.
Why the other options are wrong
- A. Electrical power loss to the boost pump is unrelated to fuel sloshing due to low tank quantity and maneuvering.
- C. Carburetor icing develops gradually and is unrelated to maneuvering-induced fuel starvation.
- D. An inadvertent selector movement would cause a sustained, not momentary, loss of fuel flow.
Fuel Tank Unporting
A condition where low fuel quantity combined with aircraft maneuvering causes fuel to shift away from the tank outlet, temporarily uncovering it and allowing air to enter the fuel line.
- Occurs with low fuel and aggressive maneuvers
- Outlet is momentarily uncovered, admitting air
- Causes brief power interruption
- Risk increases in steep turns, slips, or negative-G flight
Memory trick: Low fuel + steep turn = fuel sloshes away, outlet gasps air