Standard atmosphere. At sea level, the standard atmosphere consists of a barometric pressure of 29.92 inches of mercury ("Hg) or 1013.2 millibars, and a temperature of 15 °C (59  °F). Pressure and temperature normally decrease as altitude increases. The standard lapse rate in the lower atmosphere for each 1,000 feet of altitude is approximately 1 "Hg and 2 °C (3.5 °F). For example, the standard pressure and temperature at 3,000 feet mean sea level (MSL) is 26.92 "Hg (29.92 – 3) and 9 °C (15  °C – 6  °C). 

Standard day. See standard atmosphere. 

Standard empty weight (GAMA). This weight consists of the airframe, engines, and all items of operating equipment that have fixed locations and are permanently installed in the airplane; including fixed ballast, hydraulic fluid, unusable fuel, and full engine oil. 

Standard weights. These have been established for numerous items involved in weight and balance computations. These weights should not be used if actual weights are available. 

Standard-rate turn. A turn at the rate of 3º per second which enables the airplane to complete a 360º turn in 2 minutes. 

Starter/generator. A combined unit used on turbine engines. The device acts as a starter for rotating the engine, and after running, internal circuits are shifted to convert the device into a generator. 

Static stability. The initial tendency an aircraft displays when disturbed from a state of equilibrium. 

Station. A location in the airplane that is identified by a number designating its distance in inches from the datum. The datum is, therefore, identified as station zero. An item located at station +50 would have an arm of 50 inches. 

Stick puller. A device that applies aft pressure on the control column when the airplane is approaching the maximum operating speed. 

Stick pusher. A device that applies an abrupt and large forward force on the control column when the airplane is nearing an angle of attack where a stall could occur. 

Stick shaker. An artificial stall warning device that vibrates the control column. 

Stress risers. A scratch, groove, rivet hole, forging defect or other structural discontinuity that causes a concentration of stress. 

Subsonic. Speed below the speed of sound. 

Supercharger. An engine- or exhaust-driven air compressor used to provide additional pressure to the induction air so the engine can produce additional power. 

Supersonic. Speed above the speed of sound. 

Supplemental Type Certificate (STC). A certificate authorizing an alteration to an airframe, engine, or component that has been granted an Approved Type Certificate. 

Swept wing. A wing planform in which the tips of the wing are farther back than the wing root. 

## T 

Tailwheel aircraft. See conventional landing gear. 

Takeoff roll (ground roll). The total distance required for an aircraft to become airborne. 

Target reverser. A thrust reverser in a jet engine in which clamshell doors swivel from the stowed position at the engine tailpipe to block all of the outflow and redirect some component of the thrust forward. 

Taxiway lights. Omnidirectional lights that outline the edges of the taxiway and are blue in color. 

Taxiway turnoff lights. Flush lights which emit a steady green color. 

Tetrahedron. A large, triangular-shaped, kite-like object installed near the runway. Tetrahedrons are mounted on a pivot and are free to swing with the wind to show the pilot the direction of the wind as an aid in takeoffs and landings. 

Throttle. The valve in a carburetor or fuel control unit that determines the amount of fuel-air mixture that is fed to the engine. 

Thrust line. An imaginary line passing through the center of the propeller hub, perpendicular to the plane of the propeller rotation. 

Thrust reversers. Devices which redirect the flow of jet exhaust to reverse the direction of thrust. 

