INSTALLATION MANUAL
CMA-5024 GLSSU
This document includes Proprietary Information and shall not be reproduced or communicated to third party
without prior written permission by CMC Electronics Inc.
Page 202
November 21, 2008
C. GLSSU Checks
(1) Check for system failures
Apply power to the aircraft. Power-up the GLSSU and the associated Controller Unit (typically an
FMS) . Ensure that it does not report any GLSSU failure. Should such faults be detected, use the
interface and troubleshooting information in Appendices A to D for isolating the fault.
If the GLSSU ARINC 429 busses do not output any data and power reaches the navigation aircraft
connector J1, verify the wiring of the APD selection lines as described in Section II, paragraph 7,
and eventually correct the wiring fault. If the wiring is correct, the GLSSU is faulty and must be
replaced.
Note: If the "APD Parity Discrete Check" parameter is enabled and the APD Select Parity
discrete input (J3-16) is not set correctly, the GLSSU will enter Fault mode and will not
transmit any data on the ARINC 429 output busses.
(2) Verify the APD Selection
When the APD File contains only one APD Configuration, it is not necessary to verify the APD
Selection number since an incorrect selection is not possible.
When the approach connector J3 on the GLSSU is capped, this verification is optional considering
the high reliability of the GLSSU discrete input circuits.
Besides these two exceptions, the APD Selection number must be verified as follows, at least once
at installation time.
Note: The particular aircraft installation may provide its own automatic verification procedure. This
procedure can examine the APD CRC of the active configuration in addition to or instead of
the APD Selection number. Refer to aircraft documentation for availability of such a
procedure.
a) Obtain the APD Selection number (0 to 15) applicable to the GLSSU in this aircraft
installation.
b) Power-up the GLSSU. Using the FMS or alternate means, read the APD Selection number as it
is actually broadcast by the GLSSU over its ARINC 429 output busses, and verify it is the same
as expected.
An acceptable alternate means is using an ARINC 429 bus analyzer to capture the content of
data label 157 from the GLSSU under test. This label is transmitted on any GPS bus or GLS
bus; refer to Appendices A, B, and C for the interface and data format information. Check the
aircraft configuration to determine which bus to monitor and refer to section 2 paragraph 6 to
determine which pins to connect-to on the connector J1 of the GLSSU.
Using the bus analyzer, extract the APD Selection number from bits 26-23 of label 157 (26 is
MSB) and verify it is the same as expected.
c) If the APD Selection is not the one expected, verify the wiring of the APD selection
discrete input lines and related lines as described in Section II, paragraph 7. Then
repeat the verification procedure in subsection b) above as a final-check.
The document reference is online, please check the correspondence between the online documentation and the printed version.
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