Aeronautical Terms beginning with U

Undrainable Oil

Oil that does not drain from an engine lubricating system when the aircraft is in the normal ground attitude and the drain valve is left open. The weight of the undrainable oil is part of the empty weight of the aircraft.

Unusable Fuel

(GAMA) Fuel remaining after a runout test has been completed in accordance with governmental regulations.

Usable Fuel

(GAMA) Fuel available for flight planning.

Useful Load

(GAMA) Difference between takeoff weight, or ramp weight if applicable, and basic empty weight.

Utility Category

A category of aircraft certificated under 14 CFR part 23 and CAR part 3 that permits limited acrobatic maneuvers but restricts the weight and the CG range.