User's Manual Part 1

T
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CAS / Part No. 9000000
SYSTEM DESCRIPTION AND INSTALLATION MANUAL
34-43-20
15 Feb 2003
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1--21
4. Component Descriptions
A. TT--950/951/952 T
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CAS Computer Unit
The T
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CAS Computer Unit (CU) is the heart of the T
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CAS system consisting of an
existing TCAS 2000 LRU with a TAWS/Reactive Windshear function implemented on a
separate circuit card assembly (CCA). The TAWS/RWS function uses a processor and I/O
circuitry that is independent from the TCAS function’s processor and I/O. As such, the
software programs for TCAS and TAWS/RWS are independent from each other. By
having independent hardware, I/O and software for TCAS and TAWS/RWS, the possibility
of a commo n mode failure causing the loss of both functions is significantly reduced.
The TCAS function (CCA) contains the RF transmitter and the receivers necessary to
interrogate and receive replies from other transponder equipped aircraft. Dual
micropr ocessors are utilized to implement the surveillance and collision avoidance
algorithms. The algorithms determine whether an intruder aircraft should be considered a
threat and then determine the appropriate vertical response to avoid a midair or near
midair collision. In addition, output data is provided to drive displays that inform the flight
crew what action to take or avoid.
The TCAS function also provides an interface to the onboard Mode S transponder in
order to communicate with other TCAS ll equipped aircraft in the airspace.
The TAWS/RWS function (CCA) consists primarily of the Ground Collision Avoidance
Module (GCAM). The GCAM contains the core TAWS/Windshear algorithms which utilize
A/C state data, performance database variables and Terrain/Airport database information
to calculate required TAWS/Windshear alarms, build a terrain display buffer, and then
pass the data back to the platform. The resulting terrain information is then output to
ARINC 708A compatible weather radar or EFIS displays.
The T
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CAS CU also provides past and present LRU and system status through the front
panel mounted TEST switch and PASS/FAIL annunciators. Software updates can be
incorporated into the computer by an ARINC 603 or 615 data loader port through either
the connector mounted on the front panel of the computer or the port provided on the
LRU rear connector.
Figure 1-- 8 shows a graphical view of the TT -- 950/TT-- 952 T
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CAS Computer Unit and the
TT-- 951 T
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CAS Computer Unit. Table 1--6 provides the leading particulars.