User's Manual Part 1

T
2
CAS / Part No. 9000000
SYSTEM DESCRIPTION AND INSTALLATION MANUAL
34-43-20
15 Feb 2003
Use or disclosure of information on this page is subject to the restrictions in the proprietary notice of this document.
1--26
(1) System Interfaces
The T
2
CAS Computer Unit supports the external system interfaces that follow.
Unless otherwise specified, the specifications apply to both the TT--950/TT--952
(6 -- MCU) and TT -- 951 (4--MCU) computers. All interfaces are per ARINC 735A.
(a) Common System Interfaces
This section def ines external system interfaces th at are common to both the
TCAS function and TAWS/RWS function
1
Radio Altimeter Interface
The T
2
CAS Computer Unit accepts either analog or digital radio altimeter
inputs. For each type o f input, dual input ports are provided. The external
connector pins for Analog/Digital Radio Altitude Inputs #1 and #2 are shared
by TCAS and TAWS/RWS, which both have independent circuitry.
The T
2
CAS CU analog radio altimeter interface accepts either ARINC 552A,
Collins BCA analog input, or metric analog input formats. The T
2
CAS CU
also accepts additional radio altimeter inputs that meet the minimum TAWS
input signal requirements. The type of input format is selected by program
discrete inputs RMP--12B, --12H, --12J, and --12K. Each analog input
contains a valid discrete used to validate the analog input.
Each of the military radio altimeter types provide two outputs that are
connected to the T
2
CAS CU input pins. The two altimeter outputs are the
Analog Data Output and Analog Data Reliability signal. The T
2
CAS CU
uses the Data Reliability signal in conjunction with the Analog Data Output to
determine radio altimeter failures.
A condition exists for several military radio altimeters known as Out of T r ack.
This condition occurs when the radio altimeter has not failed and the
altimeter is not reading a valid altitude. Altitude data for an Out of Track
condition should be considered invalid and not used.
The d igital radio altimeter interface accepts inputs from an ARINC 707 radio
altimeter on ARINC 429 low speed input buses.