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LMM for the Kodiak 100
190-02102-00 Rev.4
4.7.8.9 GRS 79 Troubleshooting Questions
If possible, ask the operator the following questions to help gather the information to
accurately troubleshoot the GRS 79:
1. What specifically was the nature of the failure? Was it a red X of only heading,
only pitch/roll, or both?
2. If there was a red X of pitch or roll information, did the PFD display the AHRS
Align: Keep Wings Level message (which is indicative of an AHRS reset), or the
Attitude Fail message (which is indicative of either AHRS invalidating its output,
or a communication path failure)?
3. What exactly was the aircraft doing in the two minutes preceding the failure
(taxing on the ground, flying straight-and-level flight, turning, climbing, etc.)? If
the fault occurred on the ground, was in within 100 feet of a hanger using GPS
repeaters?
4. How long did the failure last? Was it brief or sustained? Was it repetitive in
nature? If it was repetitive, about how many times did it happen? Did it happen on
more than one day?
5. Was the fault correlated with a specific maneuver or a specific geographic area?
6. Can the fault be repeated reliably?
7. Were any of the following message advisory alerts observed within an hour of the
occurrence of the fault?
• AHRS not receiving airspeed
• AHRS using backup GPS source
• AHRS not receiving any GPS information
• AHRS not receiving backup GPS information
• AHRS magnetic-field model out of data
• AHRS extended operation in No-GPS mode
8. Did the onset of the fault occur shortly after a software upload to one or more
system LRU, or shortly after a repeat of the magnetometer calibration procedure?
9. Was a cell phone on in the aircraft at the time?
10. Were there any GPS Alert messages or loss of position lock?
4.7.8.10 GRS Troubleshooting on the Aircraft
1. Review the aircraft maintenance logbook. See if any system, other avionics, or
electrical maintenance has been performed recently.
2. Check the power wire connections at the circuit breakers. Loose wire terminals
can cause intermittent power. Also check for intermittent circuit breakers.
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