Aviation Maintenance Terms beginning with T
Tack coat
A coat of finishing material sprayed on the surface and allowed to dry until the solvents evaporate. As soon as the solvents evaporate, a wet full-bodied coat of material is sprayed over it.
Tack rag
A clean, lintless rag, slightly damp with thinner. A tack rag is used to wipe a surface to prepare it to receive a coat of finishing material.
Tack weld
A method of holding parts together before they are permanently welded. The parts are assembled, and small spots of weld are placed at strategic locations to hold them in position.
Tacky
Slightly sticky to the touch.
Tailets
Small vertical surfaces mounted underside of the horizontal stabilizer of some airplanes to increase the directional stability.
Takeoff warning system
An aural warning system that provides audio warning signals when the thrust levers are advanced for takeoff if the stabilizer, flaps, or speed brakes are in an unsafe condition for takeoff.
Tang
A tapered shank sticking out from the blade of a knife or a file. The handle of a knife or file is mounted on the tang.
Teflon
The registered trade name for a fluorocarbon resin used to make hydraulic and pneumatic seals, hoses, and backup rings.
Tempered glass
Glass that has been heat-treated to increase its strength. Tempered glass is used in bird-proof, heated windshields for high-speed aircraft.
Terminal strips
A group of threaded studs mounted in a strip of insulating plastic. Electrical wires with crimped-on terminals are placed over the studs and secured with nuts.
Terminal VOR
A low-powered VOR that is normally located on an airport.
Tetraethyl lead (TEL)
A heavy, oily, poisonous liquid, Pb(C2H5)4 , that is mixed into aviation gasoline to increase its critical pressure and temperature.
Therapeutic mask adapter
A calibrated orifice in the mask adapter for a continuous-flow oxygen system that increases the flow of oxygen to a mask being used by a passenger who is known to have a heart or respiratory problem.
Thermal dimpling
See hot dimpling.
Thermal relief valve
A relief valve in a hydraulic system that relieves pressure that builds up in an isolated part of the system because of heat. Thermal relief valves are set at a higher pressure than the system pressure relief valve.
Thermistor
A special form of electrical resistor whose resistance varies with its temperature.
Thermistor material
A material with a negative temperature coefficient that causes its resistance to decrease as its temperature increases.
Thermocouple
A loop consisting of two kinds of wire, joined at the hot, or measuring, junction and at the cold junction in the instrument. The voltage difference between the two junctions is proportional to the temperature difference between the junctions. In order for the current to be meaningful, the resistance of the thermocouple is critical, and the leads are designed for a specific installation. Their length should not be altered. Thermocouples used to measure cylinder head temperature are usually made of iron and constantan, and thermocouples that measure exhaust gas temperature for turbine engines are made of chromel and alumel.
Thermocouple fire-detection system
A fire-detection system that works on the principle of the rate-of-temperature rise. Thermocouples are installed around the area to be protected, and one thermocouple is surrounded by thermal insulation that prevents its temperature changing rapidly. In the event of a fire, the temperature of all the thermocouples except the protected one will rise immediately and a fire warning will be initiated. In the case of a general overheat condition, the temperature of all the thermocouples will rise uniformly and there will be no fire warning.
Thermoplastic resin
Atype of plastic material that becomes soft when heated and hardens when cooled.
Thermosetting resin
A type of plastic material that, when once hardened by heat, cannot be softened by being heated again.
Thermostatic expansion valve (TEV)
The component in a vapor-cycle cooling system that meters the refrigerant into the evaporator. The amount of refrigerant metered by the TEV is determined by the temperature and pressure of the refrigerant as it leaves the evaporator coils. The TEV changes the refrigerant from a high-pressure liquid into a low-pressure liquid.
Thixotropic agents
Materials, such as microballoons, added to a resin to give it body and increase its workability.
Toe-in
A condition of landing gear alignment in which the front of the tires are closer together than the rear. When the aircraft rolls forward, the wheels try to move closer together.
Toe-out
A condition of landing gear alignment in which the front of the tires are further apart than the rear. When the aircraft rolls forward, the wheels try to move farther apart.
Toroidal coil
An electrical coil wound around a ring-shaped core of highly permeable material.
Torque
A force that produces or tries to produce rotation.
Torque links
The hinged link between the piston and cylinder of an oleo-type landing gear shock absorber. The torque links allow the piston to move freely in and out of the landing gear cylinder, but prevent it rotating. The torque links can be adjusted to achieve and maintain the correct wheel alignment. Torque links are also called scissors and nutcrackers.
Torque tube
A tube in an aircraft control system that transmits a torsional force from the operating control to the control surface.
Torsion rod
A device in a spring tab to which the control horn is attached. For normal operation, the torsion rod acts as a fixed attachment point, but when the control surface loads are high, the torsion rod twists and allows the control horn to deflect the spring tab.
Total air pressure
The pressure a column of moving air will have if it is stopped.
Total air temperature
The temperature a column of moving air will have if it is stopped.
Tractor powerplant
An airplane powerplant in which the propeller is mounted in the front, and its thrust pulls the airplane rather than pushes it.
Trammel (verb)
To square up the Pratt truss used in an airplane wing. Trammel points are set on the trammel bar so they measure the distance between the center of the front spar, at the inboard compression strut, and at the center of the rear spar at the next compression strut outboard. The drag and antidrug wires are adjusted until the distance between the center of the rear spar at the inboard compression strut and the center of the front spar at the next outboard compression strut is exactly the same as that between the first points measured.
Trammel bar
A wood or metal bar on which trammel points are mounted to compare distances.
Trammel points
A set of sharp-pointed pins that protrude from the sides of a trammel bar.
Transducer
A device that changes energy from one form to another. Commonly used transducers change mechanical movement or pressures into electrical signals.
Transformer rectifier
A component in a large aircraft electrical system used to reduce the AC voltage and change it into DC for charging the battery and for operating DC equipment in the aircraft.
Translational lift
The additional lift produced by a helicopter rotor as the helicopter changes from hovering to forward flight.
Transonic flight
Flight at an airspeed in which some air flowing over the aircraft is moving at a speed below the speed of sound, and other air is moving at a speed greater than the speed of sound.
Transverse pitch
See gauge.
Triangle
A three-sided, closed plane figure. The sum of the three angles in a triangle is always equal to 180°.
Tricresyl phosphate (TCP)
A chemical compound, (CH3C6H4O)3PO, used in aviation gasoline to assist in scavenging the lead deposits left from the tetraethyl lead.
Trim tab
A small control tab mounted on the trailing edge of a movable control surface. The tab may be adjusted to provide an aerodynamic force to hold the surface on which it is mounted deflected in order to trim the airplane for hands- off flight at a specified airspeed.
Trimmed flight
A flight condition in which the aerodynamic forces acting on the control surfaces are balanced and the aircraft is able to fly straight and level with no control input.
Trip-free circuit breaker
A circuit breaker that opens a circuit any time an excessive amount of current flows, regardless of the position of the circuit breaker’s operating handle.
Troubleshooting
A procedure used in aircraft maintenance in which the operation of a malfunctioning system is analyzed to find the reason for the malfunction and to find a method for returning the system to its condition of normal operation.
True airspeed (TAS)
Airspeed shown on the airspeed indicator (indicated airspeed) corrected for position error and nonstandard air temperature and pressure.
Trunnion
Projections from the cylinder of a retractable landing gear strut about which the strut pivots retract.
Truss-type structure
A type of structure made up of longitudinal beams and cross braces. Compression loads between the main beams are carried by rigid cross braces. Tension loads are carried by stays, or wires, that go from one main beam to the other and cross between the cross braces.
Turbine
A rotary device actuated by impulse or reaction of a fluid flowing through vanes or blades that are arranges around a central shaft.
Turn and slip indicator
A rate gyroscopic flight instrument that gives the pilot an indication of the rate of rotation of the aircraft about its vertical axis. A ball in a curved glass tube shows the pilot the relationship between the centrifugal force and the force of gravity. This indicates whether or not the angle of bank is proper for the rate of turn. The turn and slip indicator shows the trim condition of the aircraft and serves as an emergency source of bank information in case the attitude gyro fails. Turn and slip indicators were formerly called needle and ball and turn and bank indicators.
Turnbuckle
A component in an aircraft control system used to adjust cable tension. A turnbuckle consists of a brass tubular barrel with right-hand threads in one end and left-hand in the other end. Control cable terminals screw into the two ends of the barrel, and turning the barrel pulls the terminals together, shortening the cable.
Twist drill
A metal cutting tool turned in a drill press or handheld drill motor. A twist drill has a straight shank and spiraled flutes. The cutting edge is ground on the end of the spiraled flutes.
Twist rope
A stripe of paint on flexible hose that runs the length of the hose. If this stripe spirals around the hose after it is installed, it indicates the hose was twisted when it was installed. Twist stripes are also called lay lines.
Two-terminal spot-type fire detection system
A fire detection system that uses individual thermoswitches installed around the inside of the area to be protected. These thermoswitches are wired in parallel between two separate circuits. A short or an open circuit can exist in either circuit without causing a fire warning.
Type Certificate Data Sheets (TCDS)
The official specifications of an aircraft, engine, or propeller issued by the Federal Aviation Administration. The TCDS lists pertinent specifications for the device, and it is the responsibility of the mechanic and/or inspector to ensure, on each inspection, that the device meets these specifications.
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