OPERATOR’S
MANUAL
CMA-9000 FLIGHT MANAGEMENT SYSTEM
Page
12-4
November 19, 2009
MILITARY GPS NAVIGATION
For installations where a dual GPS is configured with the Litton LN-100GT EGI, the FMS will also support a
military GPS navigation mode (shown as mGPS on the FMS’s POS/INIT/REF 2/X page).
In such installations when the navigation sensor cross-check option is enabled, the FMS uses a weighting logic
algorithm to compare the position provided by the military GPS to both:
•
the position provided by the hybrid INS/GPS sensor of the EGI; and
•
the position provided by the civil GPS sensor
Results of this comparison will trigger related alert messages to inform the crew of the position differences and
ensuing navigator changes.
EGI NAVIGATION
Applicable if the Embedded GPS INS (EGI) is configured.
The GPS sensor and INS complementary nature provide reliable and precise navigation even if the GPS
constellation geometry does not provide enough integrity for the route being flown.
The EGI provides a hybrid output that combines the INS and GPS outputs through a Kalman filter. This output
provides a weighted contribution of the INS and of the GPS position. When the GPS signal and constellation
geometry are adequate, the output is based on the GPS position. When the GPS signal quality degrades, the
EGI outputs in a progressive manner, with more of the INS contribution in the solution. In general, the
contribution of the INS drift, when the geometry is not optimal it remains small and allows the segment of the
route to be flown seamlessly.
In addition to the hybrid INS/GPS the EGI also provides a pure GPS and a pure INS position solutions.
The CMA-9000 FMS reverts to the pure GPS position or to another sensor when the quality factor or integrity of
the INS/GPS has degraded below what is required for the phase of flight. In this case the CMA-9000 FMS may
select the pure GPS or pure INS position (available with the Litton LN-100 GT EGI) if the remaining sensors are
not fit for navigation. Refer to General at the beginning of this Section.
The message "INS/GPS POS UNCERTAIN" or "GPS POS UNCERTAIN" is turned on if the CMA-9000 FMS is
forced to continue to use the hybrid INS/GPS or the respective GPS sensor. This happens when the GPS
position has lost integrity and there is no valid backup radio navigation sensor (DME/DME or VOR/DME).
In addition to the INS and GPS navigation mode, the SAGEM SIGMA50H EGI provides a hybrid INS/DVS
navigation solution, which is described below. The CMA-9000 FMS selects this solution according to the same
sensor selection criteria.
The GPS sensor in the EGI follows the same general behaviour as described above in Sub-Section, GPS
Navigation.
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