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 E.11
November 21, 2008
This setting does not affect the calculation of the deviations that always use the navigation
center position. Note that providing Antenna to Navigation Center Lever Arm Coefficients (X,
Y, Z Components) APD numerical values of zero will make the Navigation Center position
equal to the Antenna position.
For a TSO-C129a FMS, both settings of this APD are acceptable. Note that some equipment
may be certified to use the GPS antenna position; the outputs of type “GPS bus” can be
used for such equipment when the APD is set to On. This setting must be On when both the
Cross-Check APD and the Attitude Data Used APD are On. It must be Off when the Cross-
Check APD is On and the Attitude Data Used APD is Off.
(6) Attitude Data Used
When On, the pitch & roll & true heading data from the IRS/FMS inputs are required for the
navigation center computation.
When Off, the Navigation center computation uses a roll of zero, a heading per the FAS
Runway Heading, and a pitch per Default Aircraft Pitch APD.
Attitude data is used to increase the accuracy of the lever arm conversion.
(7) Cross-Check
When On, the GLSSU performs a cross-check of the position computation against that of the
alternate GLSSU or Sensors. When this cross-check detects a position error, the deviation
outputs will be flagged (SSM at Fail Warning); the navigation block is not affected (i.e. PVT
outputs themselves are not protected by the cross-check).
When Off, no such check is performed.
This check can be performed either be the GLSSU or in other aircraft avionics. The
requirement for a cross-check is determined by the system safety assessment. The GLSSU
can support the safety requirements of TSO-C145b/146b for fixed-wing aircraft without the
need for a cross-check. For rotary-wing aircraft, a cross-check may be required when
external attitude data is used to compute the Navigation center (refer to the Attitude Data
Used APD).
(8) Automatic SBAS PA Mode Control
When On, the entry/exit of SBAS PA mode is automatic if an approach is selected.
When Off or if no approach is selected, the GLSSU will enter SBAS PA mode only when
commanded by the SBAS PA Mode & Service Provider Selection label 305 provided the
command also specifies an SBAS PA Mode Service Provider ID different from 14 and there
are enough measurements to compute SBAS protection levels (this requires that the
Detection bit in HIL label 130 not report a satellite failure).
This setting is selected to match the capability of the user of the bus data. For typical retrofit
applications with a TSO-C129a FMS, the setting is On to allow the GLSSU to perform LPV
and LPV approaches. Only an FMS upgraded to perform SBAS LNAV/VNAV, LP, or LPV
approaches may used an Off setting; it could also retain the On when using deviations
provided by the GLSSU.
The document reference is online, please check the correspondence between the online documentation and the printed version.
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