Aviation Glossary - T

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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 temperarture.

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 - airborne receiver/transmitter portion of the SSR system which receives
the interrogation signal from the ground and automatically replies according to mode
and code selected. Modes A and B are used for identification, using a four

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.