Turbocharger.  An air compressor driven by exhaust gases, which increases the pressure of the air going into the engine through the carburetor or fuel injection system. 

Turbofan engine.  A fanlike turbojet engine designed to create additional thrust by diverting a secondary airflow around the combustion chamber. 

Turbojet engine.  A turbine engine which produces its thrust entirely by accelerating the air through the engine. 

Turboprop engine. A turbine engine which drives a propeller through a reduction gearing arrangement. Most of the energy in the exhaust gases is converted into torque, rather than using its acceleration to drive the aircraft. 

Turboshaft engine.  A gas turbine engine that delivers power through a shaft to operate something other than a propeller. 

Turn-and-slip indicator. A flight instrument consisting of a rate gyro to indicate the rate of yaw and a curved glass inclinometer to indicate the relationship between gravity and centrifugal force. The turn-and-slip indicator indicates the relationship between angle of bank and rate of yaw. Also called a turn-and-bank indicator. 

Turn coordinator.  A rate gyro that senses both roll and yaw due to the gimbal being canted. Has largely replaced the turn-and-slip indicator in modern aircraft. 

TWEB.  See Transcribed Weather Broadcast. 

## U 

UHF. See ultra-high frequency. 

Ultra-high frequency (UHF). The range of electromagnetic frequencies between 300 MHz and 3,000 MHz. 

Ulitimate 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. 

Uncaging.  Unlocking the gimbals of a gyroscopic instrument, making it susceptible to damage by abrupt flight maneuvers or rough handling. 

Uncontrolled airspace.  Class G airspace that has not been designated as Class A, B, C, D, or E. It is airspace in which air traffic control has no authority or responsibility to control air traffic; however, pilots should remember there are VFR minimums which apply to this airspace. 

Underpower.  Using less power than required for the purpose of achieving a faster rate of airspeed change. 

## United States Terminal Procedures Publication (TPP). 

Booklets published in regional format by FAA Aeronautical Navigation Products (AeroNav Products) that include DPs, STARs, IAPs, and other information pertinent to IFR flight. 

Unusual attitude.  An unintentional, unanticipated, or extreme aircraft attitude. 

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. 

User-defined waypoints.  Waypoint location and other data which may be input by the user, this is the only GPS database information that may be altered (edited) by the user. 

## V 

V$_{1}$. See takeoff decision speed. 

V$_{2}$. See takeoff safety speed. 

V$_{A}$.  See maneuvering speed. 

Vapor lock.  A problem that mostly affects gasoline-fuelled internal combustion engines. It occurs when the liquid fuel changes state from liquid to gas while still in the fuel delivery system. This disrupts the operation of the fuel pump, causing loss of feed pressure to the carburetor or fuel injection system, resulting in transient loss of power or complete stalling. Restarting the engine from this state may be difficult. The fuel can vaporize due to being heated by the engine, by the local climate or due to a lower boiling point at high altitude. 

Variation.  Compass error caused by the difference in the physical locations of the magnetic north pole and the geographic north pole. 

VASI.  See visual approach slope indicator. 

VDP.  See visual descent point. 

Vector. A force vector is a graphic representation of a force and shows both the magnitude and direction of the force. 

Vectoring.  Navigational guidance by assigning headings. 

VEF. Calibrated airspeed at which the critical engine of a multi-engine aircraft is assumed to fail. 

