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--1
SYSTEM DESCRIPTION
1. General
The T
2
CAS Traf fic and Terrain Collision Avoidance System combines a terrain awarness
warning system (TAWS) with the existing TCAS 2000 line replaceable unit (LRU) to form a
combined system (T
2
CAS). Optionally, the T
2
CAS may contain Reactive Windshear (RWS)
and/or global positioning satellite (GPS) functions within the same LRU. The integration of the
functions provides significant cost and space advantages to the customer. The
implementation method used preserves the independence of the TCAS, TAWS Reactive
Windshear and GPS functions within the T
2
CAS LRU. The system reliability for the T
2
CAS
LRU is greater than a federated system with separate TCAS, TAWS and RWS LRUs.
The TCAS function, within T
2
CAS, determines the range, altitude, and bearing of other aircraft
equipped with Mode S/Air Traffic Control Radar Beacon System (ATCRBS) transponders, with
respect to the location of own aircraft. It also monitors the trajectory of these aircraft for the
purpose of determining if any of them constitute a potential collision hazard. The TCAS
function is responsible for estimating the projected intruder track and determining if a potential
conflict exists. If so, the system displays an advisory to the pilot. The system also provides
guidance for the optimum vertical avoidance maneuver. Complementary avoidance
maneuvers between two TCAS equipped aircraft are ensured by coordination of mutual
intentions with the other aircraft through the Mode S Transponders. T
2
CAS TCAS meets the
requirements of TSO -- C119b.
The T
2
CAS TAWS function, within the T
2
CAS, pr ovides both Collision Prediction and Alerting
(CPA) as well as conventional Ground Proximity Warning System (GPWS) modes of
operation. The CPA uses data provided by the Flight Management Computer, the GPS
receiver, and other aircraft subsystems to predict a 3-- D flight path based upon a curve--fit
extrapolation of the most recent position and velocity data received. This predicted flight path
is then compared with the internal terrain profile of the immediate area and the CPA algorithm
computes an assessment of the potential threat of aircraft collision with terrain. When
operative, CPA replaces RTCA DO--161A reactive modes 1 and 2 since it offers superior
safety margins for controlled flight into terrain (CFIT) prevention due to its predictive
capabilities. Since modes 1 and 2 are the prima ry source of nuisance alerts, suppressing
these alerts greatly reduces the nuisance alert rate and thus improves pilot confidence in the
system. T
2
CAS TAWS meets the requirements of TSO -- C151a Class A.
A Reactive Windshear function is integrated in T
2
CAS when necessary to meet the aircraft
application, and meets the requirements of TSO--C117a.
The T
2
CAS RWS function 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 Warning algorithm continuously
monitors wind factors that affect aircraft performance on both take-- o ff and landing approach,
in order to identify the presence of a severe low -- level, downburst/microburst--type shear. If
these wind factors cause aircraft performance to decrease to a predetermined level, an audio
warning is sounded, indicating to the crew that the aircraft net performance capability is
deteriorating and rapidly approaching a critical state. In addition to the warning, the
Windshear Warning algorithm provides a caution when an increasing--performance Windshear
is detected, thus giving advance warning of decreasing -- performance windshear.