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6/17/21 

Pilot/Controller Glossary 

a gate printer. In addition, TDLS will emulate the 
Flight Data Input/Output (FDIO) information within 
the control tower. 

TERMINAL RADAR SERVICE AREA

 Airspace 

surrounding designated airports wherein ATC 
provides radar vectoring, sequencing, and separation 
on a full-time basis for all IFR and participating VFR 
aircraft. The AIM contains an explanation of TRSA. 
TRSAs are depicted on VFR aeronautical charts. 
Pilot participation is urged but is not mandatory. 

TERMINAL VFR RADAR SERVICE

 A national 

program instituted to extend the terminal radar 
services provided instrument flight rules (IFR) 
aircraft to visual flight rules (VFR) aircraft. The 
program is divided into four types service referred to 
as basic radar service, terminal radar service area 
(TRSA) service, Class B service and Class C service. 
The type of service provided at a particular location 
is contained in the Chart Supplement U.S. 

a. 

Basic Radar Service

 These services are 

provided for VFR aircraft by all commissioned 
terminal radar facilities. Basic radar service includes 
safety alerts, traffic advisories, limited radar 
vectoring when requested by the pilot, and 
sequencing at locations where procedures have been 
established for this purpose and/or when covered by 
a letter of agreement. The purpose of this service is to 
adjust the flow of arriving IFR and VFR aircraft into 
the traffic pattern in a safe and orderly manner and to 
provide traffic advisories to departing VFR aircraft. 

b. 

TRSA Service

 This service provides, in 

addition to basic radar service, sequencing of all IFR 
and participating VFR aircraft to the primary airport 
and separation between all participating VFR 
aircraft. The purpose of this service is to provide 
separation between all participating VFR aircraft and 
all IFR aircraft operating within the area defined as a 
TRSA. 

c. 

Class C Service

 This service provides, in 

addition to basic radar service, approved separation 
between IFR and VFR aircraft, and sequencing of 
VFR aircraft, and sequencing of VFR arrivals to the 
primary airport. 

d. 

Class B Service

 This service provides, in 

addition to basic radar service, approved separation 

of aircraft based on IFR, VFR, and/or weight, and 
sequencing of VFR arrivals to the primary airport(s). 

(See CONTROLLED AIRSPACE.) 
(See TERMINAL RADAR SERVICE AREA.) 
(Refer to AIM.) 
(Refer to CHART SUPPLEMENT U.S.) 

TERMINAL-VERY HIGH FREQUENCY OMNI-
DIRECTIONAL 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. 

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.) 

TF

 

(See TERRAIN FOLLOWING.) 

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.) 

PCG T