Track  (1) The actual path, over the ground,traveled by an aircraft (navigation). (2) In this mode the DME transmits a reduced pulse pair rate after acquiring lock-on (DME). (3) Estimated position and velocity of a single aircraft based on correlated surveillance data reports (TCAS). 
TRACON  Terminal Radar Approach Control 
TRACS  Test and Repair Control System. An automated data retrieval system. TRACS functions include:1) provide the location of any given unit at any time;2) provide an efficient flow of work to and from test stations;3) provide quick access to quality information generated by the actual testing process (performed by the tech-nician); (4) provide statistical and historical data regarding throughput time for products, failure,yield rates,WIP, etc. 
Traffic Advisory  Information given to the pilot pertaining to the posi tion of another aircraft in the immediate vicinity. The information contains no suggested maneuvers. (Traffic advisory airspace is 1200 feet above and below the aircraft and approximately 45 seconds dis tant with respect to closure speed of the aircraft.) [TCAS] 
Traffic Density  The number of transponder-equipped aircraft within R nautical miles (nmi) of own aircraft,divided by p x (R nmi).. Transponder-equipped aircraft include Mode-S and ATCRBS Mode A and Mode C, and excludes own aircraft (TCAS). 
Transceiver  A receiver and transmitter combined in a single unit. Same as RT. 
Transponder  Avionics equipment that returns an identifying coded signal. 
TRK  Track 
TRP  (1) Mode S Transponder (2) ARPA Technology Reinvestment Program 
TRR  Test Rejection and Repair 
TRSB  Time Reference Scanning Beam. The international standard for MLS installations. 

TRU Transformer Rectifier Unit
True Airspeed The true velocity of the aircraft through the surround-TWP Technical Work Program
ing air mass. 
True Altitude  The exact distance above mean sea level (corrected 
for temperature). 
True Bearing  The bearing of a ground station with respect to true 
north. 
True North  The direction of the north pole from the observer.