ULTIMATE LOAD FACTOR— In stress analysis, the load that causes physical breakdown in an aircraft or aircraft component during a strength test, or the load that according to computations, should cause such a breakdown.

UNFEATHERING ACCUMULATOR—Tanks that hold oil under pressure which can be used to unfeather a propeller.

UNICOM— A nongovernment air/ground radio communication station which may provide airport information at public use airports where there is no tower or FSS.

UNUSABLE FUEL—Fuel that cannot be consumed by the engine. This fuel is considered part of the empty weight of the aircraft.

USEFUL LOAD—The weight of the pilot, copilot, passengers, baggage, usable fuel, and drainable oil. It is the basic empty weight subtracted from the maximum allowable gross weight. This term applies to general aviation aircraft only.

UTILITY CATEGORY— An airplane that has a seating configuration, excluding pilot seats, of nine or less, a maximum certificated takeoff weight of 12,500 pounds or less, and intended for limited acrobatic operation.