aviation glossary


T - true. Also TH, true heading, and TT, true track.

TACAN - tactical air navigation system. An ultra-high frequency electronic navigation aid which provides suitably-equipped aircraft with a continuous indication of bearing and distance to the selected Tacan station. The distance element can be received by civilian DMF equipment, but otherwise Tacan is principally a military navaid.

TAF - Terminal Area Forecast.

TAS - true airspeed. Rectified airspeed corrected for altitude and outside air temperature.

TBO - time between overhauls, an engine manufacturer's recommended overhaul interval in hours, a rough and not guaranteed guide to life expectancy of an aero-engine before it will need overhaul.

TCA - Terminal Control Area (USA).

TCAS - traffic alert and collision avoidance system. U.S. developed radar-based airborne collision avoidance system operating independently of ground-based equipment. TCAS-I generates traffic advisories only, TCAS-II provides advisories and collision avoidance instructions in the vertical plane.

TEMPO - temporarily, term used in Met reports.

TET - turbine entry temperature.

TGT - turbine gas temperature.

THR or thld - threshold.

TMA - Terminal Control Area. An area of controlled airspace at the intersection of airways in the vicinity of control zones (CTRs) around major airports.

TO - take-off (sometimes TKOF).

TODA - take-off distance available. Also TODR, take-off distance required, and TORA, take-off run available.

track - actual flight path of an aircraft over the ground.

transition altitude (TA) - altitude in the vicinity of an aerodrome at or below which the vertical position of an aircraft is controlled by reference to altitude, i.e. with the aerodrome

QNH set on its altimeter. Above transition altitude QNE is set and flight levels used. Also transition level (TL) at which a descending aircraft changes from FL to QNH.

transponder - An electronic device that "responds" to interrogation by ground-based radar with a special four-digit code that specifically identifies the aircraft on which it is located. Certain transponders have the ability to transmit automatically the altitude of the aircraft in addition to the special code.

trend - Met forecast for the next two hours, added to some METARs.

TSO - Technical Standard Order. A standard established by the U.S. FAA for quality control in avionics, instruments and other airborne equipment. If it complies, equipment is said to be 'TSO'd' and is more expensive than similar non-TSO's equipment.

TVOR - terminal VOR. A low-powered VOR located at or near an airport and used as an approach aid.

TWR - Tower (aerodrome control tower).

TWY - taxiway.

Tx - transmitter.