Pilot/Controller Glossary TERMINAL-VERY HIGH FREQUENCY OMNIDIRECTIONAL RANGE STATION (TVOR)- A very high frequency terminal omnirange station located on or near an airport and used as an approach aid. (See NAVIGATIONAL AID.) (See VOR.) TERRAIN AWARENESS WARNING SYSTEM (TAWS)- An on-board, terrain proximity alerting system providing the aircrew "Low Altitude warnings" to allow immediate pilot action. TERRAIN FOLLOWING- The flight of a military aircraft maintaining a constant AGL altitude above the terrain or the highest obstruction. The altitude of the aircraft will constantly change with the varying terrain and/or obstruction. TF- (See TERRAIN FOLLOWING.) TFDM- (See TERMINAL FLIGHT DATA MANAGER.) TGUI- (See TIMELINE GRAPHICAL USER INTERFACE.) THAT IS CORRECT- The understanding you have is right. THA- (See TRANSITIONAL HAZARD AREA.) THREE-HOUR TARMAC RULE" Rule that relates to Department of Transportation (DOT) requirements placed on airlines when tarmac delays are anticipated to reach 3 hours. 360 OVERHEAD- (See OVERHEAD MANEUVER.) THRESHOLD- The beginning of that portion of the runway usable for landing. (See AIRPORT LIGHTING.) (See DISPLACED THRESHOLD.) (See GLIDESLOPE.) (See THRESHOLD.) THRESHOLD LIGHTS- (See AIRPORT LIGHTING.) TIE-IN FACILITY" The FSS primarily responsible for providing FSS services, including telecommuni ca ti on s se rv i ce s fo r la nd in g f ac il it ie s o r navigational aids located within the boundaries of a flight plan area (FPA). Three-letter identifiers are assigned to each FSS/FPA and are annotated as tie-in facilities in the Chart Supplement U.S., the Alaska Supplement, the Pacific Supplement, and FAA Order JO 7350.9, Location Identifiers. Large consolidated FSS facilities may have many tie-in facilities or FSS sectors within one facility. yutsrpon TETRAHEDRON- A device normally located on uncontrolled airports and used as a landing direction indicator. The small end of a tetrahedron points in the direction of landing. At controlled airports, the tetrahedron, if installed, should be disregarded because tower instructions supersede the indicator. (See SEGMENTED CIRCLE.) (Refer to AIM.) THRESHOLD CROSSING HEIGHT- The theoretical height above the runway threshold at which the aircraft"s glideslope antenna would be if the aircraft maintains the trajectory established by the mean ILS glideslope or the altitude at which the calculated glidepath of an RNAV or GPS approaches. (See FLIGHT PLAN AREA.) (See FLIGHT SERVICE STATION.) TIME-BASED FLOW MANAGEMENT (TBFM)- A foundational Decision Support Tool for time-based management in the en route and terminal environments. TBFM"s core function is the ability to schedule aircraft within a stream of traffic to reach a defined constraint point (e.g., meter fix/meter arc) at specified times, creating a time-ordered sequence of traffic. The scheduled times allow for merging of traffic flows, efficiently utilizing airport and airspace capacity while minimizing coordination and reducing the need for vectoring/holding. The TBFM schedule is calculated using current aircraft estimated time of arrival at key defined constraint points based on wind forecasts, aircraft flight plan, the desired separation at the constraint point and other parameters. The schedule applies spacing only when needed to maintain the desired separation at one or more constraint points. This includes, but is not limited to, Single Center Metering (SCM), Adjacent Center Metering (ACM), En Route Departure Capability (EDC), Integrated Departure/Arrival Capability (IDAC), Ground-based Interval Management-Spacing (GIM-S), Departure Scheduling, and Extended/Coupled Metering. TIME-BASED MANAGEMENT (TBM)- A methodology for managing the flow of air traffic