Pilot/Controller Glossary

Information Service (D-ATIS) both on a specified
radio frequency and also, for subscribers, in a text
message via data link to the cockpit or to a gate
printer. TDLS also provides Pre-departure Clearances (PDC), at selected airports, to subscribers,
through a service provider, in text to the cockpit or to
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 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.
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.
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.)

THRESHOLD CROSSING HEIGHT- The
theoretical height above the runway threshold at