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 D.3
November 21, 2008
If no labels are output by the GLSSU, it is most likely faulty and shall be replaced. However, if the ILS
or DME bus outputs of the GLSSU are found faulty the activity on its ILS and DME input busses shall
be verified also, as per the section 1.3 below, since the HIS is intended to pass-through the DME/ILS
input data.
If the labels are actually output, check also if the SSM bits of label 273 are set to the Normal Operation
(data bits 31-30 = 00). If the SSM bits are Normal Operation and the receiving equipment does not
accept or display the GPS operational mode from label 273, the fault may reside in the receiving
equipment or in the aircraft interwiring, such as wiring error, polarity reversal, short-circuits, open-
circuits, or plain failure of a remote aircraft system.
1.2 GLSSU ARINC 429 INPUT INTERFACE CHECKS
Check the ARINC 429 label 355 on a GLSSU ARINC 429 output bus at the J1 cable connector end.
Ensure that the SDI bits of this data word are identical to the GLSSU SDI settings.
Using the data label 355, check for faults as per the table below. For bit assignments details, refer to
Appendix A. If bits 27... 25 are “000” (Normal), there are no faults; the states of bits 24... 18 depend on
actual aircraft interwiring of the ARINC 429 inputs. If a fault is reported, bit 26 reports it is an antenna or
RF cable fault. Perform corrective action or further fault isolation as indicated in the table. Note that
abnormal RF interference may be reported as a fault. If the bus seems inactive, check its activity as
said later.
CAUTION: The GLSSU must be re-initialized prior to testing, whenever the discrete or ARINC 429
input wiring is modified, because some discrete inputs are read only at start-up and the
ARINC 429 inputs determine their bus speed at start-up. Refer to Appendix A.
BITS DESCRIPTION SETTING DIAGNOSTIC ACTION
32 Parity Odd parity Parity error Check for bad bus wiring &
noise. Replace GLSSU
Normal Operation = 00 No faults detected No action
No Computed Data = 01 Should not occur Replace GLSSU
Functional Test = 10 Should be a
momentary state
If steady, replace GLSSU
31,
30
Sign Status Matrix
(SSM)
Failure Warning = 11 Should not occur Replace GLSSU
No Acknowledge = 0 No action 29 Command Word
Acknowledge
Acknowledge = 1 No action
Test Allowed =0 No action 28 Test Inhibit
Inhibited =1 No action
Normal Op = 0 No action 27 Sensor Unit
Fail = 1 Internal fault Replace GLSSU
Normal Op = 0 No action 26 RF Input
Fail = 1 Defective antenna
preamplifier; RF cable
damaged or cut
Check antenna, RF cable
25 GPS Normal Op = 0 No action
The document reference is online, please check the correspondence between the online documentation and the printed version.
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