TCAS II V7.1 Intro booklet

The TCAS Solution
After many years of extensive analysis,
development, and flight evaluation by the
Federal Aviation Administration (FAA),
other countries’ Civil Aviation Authorities
(CAAs), and the aviation industry, Traffic
Alert and Collision Avoidance System or
TCAS was developed to reduce the risk of
mid-air collisions between aircraft. In the
international arena, this system is known
as the Airborne Collision Avoidance
System or ACAS.
TCAS is a family of airborne devices that
function independently of the ground-based
air traffic control (ATC) system, and
provide collision avoidance protection for a
broad spectrum of aircraft types. All TCAS
systems provide some degree of collision
threat alerting, and a traffic display. TCAS I
and II differ primarily by their alerting
capability.
TCAS I provides traffic advisories (TAs) to
assist the pilot in the visual acquisition of
intruder aircraft. TCAS I is mandated for
use in the U.S. for turbine powered,
passenger-carrying aircraft having more than
10 and less than 31 seats. TCAS I is also
installed on a number of general aviation
fixed wing aircraft and helicopters.
TCAS II provides TAs and resolution
advisories (RAs), i.e., recommended escape
maneuvers, in the vertical dimension to
either increase or maintain the existing
vertical separation between aircraft.
TCAS II is mandated by the U.S. for
commercial aircraft, including regional
airline aircraft with more than 30 seats or a
maximum takeoff weight greater than
33,000 lbs. Although not mandated for
general aviation use, many turbine-powered
general aviation aircraft and some
helicopters are also equipped with TCAS II.
The TCAS concept makes use of the same
radar beacon transponders installed on
aircraft to operate with ATC’s ground-based
radars. The level of protection provided by
TCAS equipment depends on the type of
transponder the target aircraft is carrying.
The level of protection is outlined in
Table 1. It should be noted that TCAS
provides no protection against aircraft
that do not have an operating
transponder.
Target Aircraft Equipment
Table 1. TCAS Levels of Protection
Mode A
XPDR
ONLY
Mode C
or Mode S
XPDR
Own Aircraft Equipment
TCAS I TCAS II
TA TA
TA
TA and
Vertical RA
TCAS I TA TA and
Vertical RA
TCAS II TA TA and
Coordinated
Vertical RA
Early Collision Avoidance
Systems
The 1956 collision between two airliners
over the Grand Canyon spurred both the
airlines and aviation authorities to initiate
development of an effective collision
avoidance system that would act as a last
resort when there is a failure in the ATCprovided
separation services. During the
late 1950’s and early 1960’s, collision
avoidance development efforts included an
emphasis on passive and non-cooperating
systems. These concepts proved to be
impractical. One major operational problem
that could not be overcome with these
designs was the need for non-conflicting,
complementary avoidance maneuvers which
require a high-integrity communications link
between aircraft involved in the conflict.
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