Torquemeter.  An instrument used with some of the larger  reciprocating engines and turboprop or turboshaft engines to  measure the reaction between the propeller reduction gears  and the engine case.  Total drag.  The sum of the parasite drag and induced drag.  Touchdown zone elevation (TDZE).  The highest elevation  in the first 3,000 feet of the landing surface, TDZE is  indicated on the instrument approach procedure chart when  straight-in landing minimums are authorized.  Touchdown zone lights.  Two rows of transverse light bars  disposed symmetrically about the runway centerline in the  runway touchdown zone.  Tower En Route Control (TEC).  The control of IFR  en route traffic within delegated airspace between two  or more adjacent approach control facilities, designed to  expedite traffic and reduce control and pilot communication  requirements.  TPP.  See United States Terminal Procedures Publication.  Track.  The actual path made over the ground in flight.  Tracking.  Flying a heading that will maintain the desired  track to or from the station regardless of crosswind conditions.  Traffic Alert Collision Avoidance System (TCAS).  An airborne system developed by the FAA that operates  independently from the ground-based Air Traffic Control  system. Designed to increase flight deck awareness of  proximate aircraft and to serve as a “last line of defense” for  the prevention of midair collisions.  Traffic information service (TIS).  A ground-based service  providing information to the flight deck via data link using  the S-mode transponder and altitude encoder to improve the  safety and efficiency of “see and avoid” flight through an  automatic display that informs the pilot of nearby traffic.  Trailing edge.  The portion of the airfoil where the airflow  over the upper surface rejoins the lower surface airflow.  Transcribed Weather Broadcast (TWEB).  An FSS service,  available in Alaska only, providing continuously updated  automated broadcast of meteorological and aeronautical data  over selected L/MF and VOR NAVAIDs.  Transponder.  The airborne portion of the ATC radar  beacon system.  Turbine engine.  An aircraft engine which consists of an  air compressor, a combustion section, and a turbine. Thrust  is produced by increasing the velocity of the air flowing  through the engine.  Turbine discharge pressure.  The total pressure at the  discharge of the low-pressure turbine in a dual-turbine axial- flow engine.  T-tail.  An aircraft with the horizontal stabilizer mounted on  the top of the vertical stabilizer, forming a T.  Truss.  A fuselage design made up of supporting structural  members that resist deformation by applied loads. The truss- type fuselage is constructed of steel or aluminum tubing.  Strength and rigidity is achieved by welding the tubing  together into a series of triangular shapes, called trusses.  True altitude.  The vertical distance of the airplane above  sea level—the actual altitude. It is often expressed as feet  above mean sea level (MSL). Airport, terrain, and obstacle  elevations on aeronautical charts are true altitudes.  True airspeed.  Actual airspeed, determined by applying a  correction for pressure altitude and temperature to the CAS.  Troposphere.  The layer of the atmosphere extending from  the surface to a height of 20,000 to 60,000 feet, depending  on latitude.  Tropopause.  The boundary layer between the troposphere  and the stratosphere which acts as a lid to confine most of the  water vapor, and the associated weather, to the troposphere.  Trim tab.  A small auxiliary hinged portion of a movable  control surface that can be adjusted during flight to a position  resulting in a balance of control forces.  Trim.  To adjust the aerodynamic forces on the control  surfaces so that the aircraft maintains the set attitude without  any control input.  Tricycle gear.  Landing gear employing a third wheel located  on the nose of the aircraft.  Trend.  Immediate indication of the direction of aircraft  movement, as shown on instruments.  Transponder code.  One of 4,096 four-digit discrete codes  ATC assigns to distinguish between aircraft.  G-31 