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LMM for the Kodiak 100
Page 4-87
190-02102-00 Rev.4
When taxiing without reliable GPS information, heading performance is susceptible to
the presence of magnetic anomalies (metal buildings, underground steel culverts, steel
grates in the ramp). Localized sources of interference on the ground might consistently
red X the heading in the same spot while taxiing, this is not caused by a failure of the
GMU 44 or its calibration. If no observable steel structures are present, the red X is most
likely caused by an unseen underground disturbance. To confirm this, the heading will
repeatedly red X in the same area during multiple taxi runs. The GRS 79 might invalidate
(red X) the heading if the following are present: it does not have GPS information, it
senses a magnetic anomaly and senses aircraft movement. Remove those influences to
find if one of them caused the red X.
When the aircraft is on the ground and stationary, the aircraft yaw rate must be less than
1.5 degrees/second to use GPS track information to calculate heading. This logic is
applied regardless of magnetic anomaly detection. This could cause a heading red X if
the aircraft is moving due to wind, operators entering/exiting the aircraft or any other
disturbance that moves the wings and tail.
4.7.8.12 GMU Communications
The GMU status on the System Status page indicates the health of the GRS 79 to GMU
44 RS-232 data path. If a red X is present for the GMU, check the RS-232 data path for
faults before replacing any unit.
4.7.8.13 GRS 79 Calibration Message
The external installation configuration parameters are not considered calibrated. These
parameters are categorized into 2 sets: AHRS installation, and magnetic installation
parameters. If either of the two is NOT CALIBRATED, the GRS 79 heading, pitch, and
roll might all be flagged as invalid, or a message displayed (see
Figure 4-16. GRS Calibration Message
Perform the required post-installation calibration procedures. If the calibration is
unsuccessful, the GRS configuration module might require replacement since it stores
the calibration information.
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