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 207
November 21, 2008
Should a significant effect be apparent, the test condition should be briefly removed and reapplied a few
times, in order to confirm the effect and to eliminate coincidences and normal noise fluctuations or
navigation mode changes. Check also for obvious external factors such as mobile radios and cellular
phones, nearby vehicles and other aircrafts, etc....
A harmful RF interference condition should be declared when the pattern of the effects is found related
systematically to the applied test pattern.
B. Set-up
The aircraft should be located in an area where the GPU or APU and later the engines may be run to
supply power to the aircraft's avionic and hydraulic systems. Position the aircraft in an area clear of
surrounding obstructions and electromagnetic interference.
Apply battery power to a GLSSU and to the CDU and aircraft systems required for displaying the
GLSSU status. Ensure that all other electrical systems are shutdown so that a baseline condition with
minimum RF interference will exist.
Using the CDU of an FMS or alternate means, verify that the GLSSU is in Navigation Mode (NAV), in
SBAS Navigation Mode (SBAS NAV) or in SBAS PA mode. If not, ensure that the aircraft is located
outside hangars in an unobstructed area free of RF interference. Then observe and record the sample
test data in the table below, to serve as a baseline for following the RF interference tests. The data
items are reported by the GLSSU on label 273; refer to Appendix B for the data format.
DATA ITEM TEST RESULT TYPICAL RANGE COMMENT
Number of visible
satellites
0…16
Number of satellites
used in the navigation
solution
0…12 maximum
Navigation mode NAV or SBAS NAV or
SBAS PA
Note: As a minimum, the GLSSU should track 4 or 5 satellites otherwise it would not be able to
enter the navigation modes. The number of satellites reported visible by the GLSSU may be
much larger. How many satellites are actually visible and being tracked is not easily
predictable, depending upon local time and conditions.
Note: Due to the apparent satellite movements and line-of-sight obstructions, the baseline test
results will vary with time and should be updated about every half hour.
The document reference is online, please check the correspondence between the online documentation and the printed version.
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