Aviation Maintenance Terms beginning with U
Ultrasonic inspection
Uses high frequency sound energy to conduct examinations and make measurements. Ultrasonic inspection can be used for flaw detection/evaluation, dimensional measurements, and material characterization.
Useful load
Fuel, any other fluids that are not part of empty weight, passengers, baggage, pilot, copilot, and crewmembers. It is determined by subtracting the empty weight from the maximum allowable gross weight
Underspeed condition
A speed condition in which the engine is turning at an RPM lower than that for which the propeller governor is set.
Unidirectional fibers
Fibers in a piece of composite material arranged so that they sustain loads in only one direction.
Updraft carburetor
A carburetor that mounts on the bottom of a reciprocating engine. Air entering the engine flows upward through the carburetor.
Upper-deck pressure
The absolute pressure of air at the inlet to the fuel metering system of a turbocharged engine. Upper-deck pressure is the same as the turbocharger discharge pressure.
Ultimate tensile strength
The tensile strength required to cause a material to break or to continue to deform under a decreasing load.
Ultraviolet-blocking dope
Dope that contains aluminum powder or some other pigment that blocks the passage of ultraviolet rays of the sun. The coat of dope protects the organic fabrics and clear dope from deterioration by these rays.
Undamped oscillation
Oscillation that continues with an unchanging amplitude once it has started.
Underslung rotor
A helicopter rotor whose center of gravity is below the point at which it is attached to the mast.
Unidirectional fabric
Fabric in which all the threads run in the same direction. These threads are often bound with a few fibers run at right angles, just enough to hold the yarns together and prevent their bunching.
Unloading valve
This is another name for system pressure regulator. See system pressure regulator.
Utility finish
The finish of an aircraft that gives the necessary tautness and fill to the fabric and the necessary protection to the metal, but does not have the glossy appearance of a show-type finish.
Unmanned aircraft
An aircraft operated without the possibility of direct human intervention from within or on the aircraft.
Unmanned aircraft system
An unmanned aircraft and its associated elements (including communication links and the components that control the unmanned aircraft) that are required for the safe and efficient operation of the unmanned aircraft in the airspace of the United States.
Unbonding
Adhesive or cohesive failure between laminates. Compare definitions of adhesive, cohesive debond, and disbond.
Uncompensated Latency
Any latency in the ADS-B system that is not compensated through extrapolation. Uncompensated latency can be represented as the difference between the time of applicability of the broadcast position and the actual time of transmission.
Universal Access Transceiver (UAT)
A wideband multipurpose data link intended to operate globally on a single channel with a channel signaling rate of just over 1Mbps. By design, UAT supports multiple broadcast services including FIS-B and TIS-B in addition to ADS-B. This is accomplished using a hybrid medium access approach that incorporates both time-slotted and random unslotted access.
Undercutting
A rubber fracture that progresses from the tread surface, or in a groove, in a direction parallel to the ply structure.