INSTALLATION MANUAL
CMA-5024 GLSSU
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Page 203
November 21, 2008
(3) Functional/Guidance Tests
a) Functional Test
The GLSSU will automatically perform a Functional test at power on. Use the FMS or alternate
means to monitor the data label 355 on one of the ARINC 429 bus output (GLS or GPS bus)
from the GLSSU. An acceptable alternate means is an ARINC 429 bus monitor, connected to
observe the data label 355 and its SSM bits. Refer to Appendix C for the label format and
interpreting the result of this test.
The Functional test lasts for about 10 seconds total. During the test, the GLSSU does not
output navigation data and the SSM bits of data label 355 are set to "Functional Test". Keep
monitoring the SSM bits of data label 355 and check they are set to "Functional Test".
When the data flows again, check that the SSM bits of data label 355 returns to "Normal" and
monitor the faults bits: Bits 25, 26, 27 of label 355. These bits will be reset automatically by the
next test be it a Functional test or a continuous test. Even if a continuous BITE clears the fault,
the bits will still report the fault for a total of about 30 seconds.
If any of these bits is set, a fault has been detected and the GLSSU is defective. For severe
faults, the GLSSU also reports FAULT mode on label 273.
Note: Excessive external RF interference can cause the GLSSU to report a fault on label
355; the GLSSU will not be in FAULT mode. This possibility should be considered
before declaring the GLSSU to be defective.
The Functional test may also be triggered manually in some installations. To allow this, ensure
first that the internal Air/Ground state is "Ground". This can be verified on label 355 bit 28 as
test is allowed only on ground. The GLSSU determines the internal Air/Ground state using the
following data inputs:
- Internal and external ground speed data (decision threshold: 40 to 50 Kt),
- Bit 19 of ARINC 429 input label 151or bit 27 of ARINC 429 input label 272,
- The Air/Ground input discrete on connector J1.
Refer to Appendix E for the related APD parameter "Air/Ground Discrete Open In Air".
For activating manually the self-test, ground the Functional / Guidance Test discrete input; the
self-test will begin typically within 5 seconds (within 10 seconds maximum). Another alternative
is using the FMS or alternate means to activate the Functional test; refer to the applicable
equipment manual. An acceptable alternate means is using an ARINC 429 bus emulator for
sending the functional test command on the Command Summary Word, label 227; refer to
Appendices A and C for information.
b) Guidance Tests
For Class Delta 4 installations, the tests in this subsection should be repeated to verify in turn
each GLS and ILS output bus connected to a deviation display.
The document reference is online, please check the correspondence between the online documentation and the printed version.
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