User's Manual Part 1

T
2
CAS / Part No. 9000000
SYSTEM DESCRIPTION AND INSTALLATION MANUAL
34-43-20
15 Feb 2003
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1--6
3. System Description
The T
2
CAS is a safety system that combines TCAS, Terrain Awareness and Warning System
(TAWS), and optionally Reactive Windshear (RWS) and/or GPS functions in a single LRU.
The TCAS function is an onboard advisory system designed to act as a backup to the air
traffic control (ATC) radar and the “see and avoid” procedures. By computing the closure rate
and altitude of all transponder equipped aircraft in the surrounding airspace, the TCAS can
anticipate a potential midair collision before it has a chance to materialize.
TCAS continually plots local air traffic on the associated display, and in the event of a
conflicting flightpath, guides the pilot towards the correct avoidance maneuver. If the intruding
aircraft is also equipped with a TCAS II compatible system, the two systems can communicate
their mutual intentions through the Mode S transponders. The coordinated advisories that
result allow the two pilots to execute complementary avoidance maneuvers.
TCAS complies with ARINC Characteristic 735a (TCAS) and the requirements of TSO--C119b.
The TAWS function within T
2
CAS features an innovative design aimed at preventing CFIT
(Controlled Flight Into Terrain) accidents by p roviding timely aircrew alerts. The alerts are
based upon predicted terrain clearance profiles calculated with present aircraft climb
capabilities. This represents a significant advance in capability from the present Ground
Proximity Warning System (GPWS) technology, and a significant improvement in CFIT safety
margins over existing Terrain Awareness and Warning System (TAWS) designs:
• By providing warnings based on remaining time before pilot response is required and not
based on remaining time to terrain impact
• By covering more operational situations
• By drastically minimizing nuisance alerts.
As an optional part of the TAWS system, T
2
CAS incorporates a Reactive Windshear feature
as part of its basic functionality. It conforms to the Windshear Warning capabilities described
in TSO C117a without the guidance feature. The Reactive Windshear function monitors wind
factors that affect aircraft performance on both take--off and landing approach, in order to
identify the presence of a severe low --level, downburst/microburst -- type windshear.
A. System Functional Description
(1) TCAS Functional Description
Situational awareness is provided to the flight crew by aiding in visually acquiring
intruding aircraft and discriminating between the intruding aircraft, threat aircraft, and
other traffic in the airspace.
Vertical guidance to avoid midair collisions is accomplished by interrogating the Mode
A, Mode C, and Mode S transponders of potential threat aircraft, tracking their
responses, and providing advisories to the flight crew to assure vertical separation.