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Tachometer: A device for measuring angular velocity.

Tactical Air Navigation: A basic guidance mode, providing lateral guidance to a TACAN station; equipment that determines range and bearing to a radio station with a TACAN transmitter.

Terrain following (TF): A basic guidance mode, providing vertical guidance to maintain an operator selected radar altitude above the terrain. Flight such that the aircraft tries to maintain a constant height above the terrain, usually in the range of 100-1,000 ft; uses a g-command from the Multi-Mode Radar to generate a flight director cue. This controls the aircraft flight path so that the set clearance altitude is achieved over major high points in the terrain with zero flight path angle.

Terrain Referenced Navigation (TRN): A navigation mode based on comparison of barometric altitude and radar altitude with a map; Kalman filters correlate the terrain data and the altitudes. TRN combines INS with map references. It is most accurate over rough terrain; however it does not give accurate data while over flat areas or water.

Terrain: The contour of the earth.

Third Party Litigation: When a lawsuit is brought against a defendant and that defendant wants to add another party to the suit, the original defendant may file a “third party complaint” which results in a third party litigation or lawsuit.

Throttle: A flight control operated by moving fore or aft with hands, primarily to control thrust (speed) in fixed-wing aircraft.

Thrust: Force, created by engines and rotors, acting in the direction of the engine. 

Time constant: Constant for a first-order filter determining time at which the output of the filter reaches nearly 0.6321 percent of a step input. 

Tort: A civil wrong; a wrongful injury to a person’s property. There are three types of torts: intentional, negligence and strict liability.

Total pressure: A measure of barometric pressure in the moving air.

Track (TRK): A basic guidance mode, providing lateral guidance to an operator selected ground track. 

Transmitter: A device that transmits. 

True airspeed (TAS): Airspeed corrected for instrumentation errors and air density.