G1000 Supplemental Maintenance Manual Page 5-11Textron Nav III Series Revision 3190-02128-04Invalid Data Field Associated LRU(s) SolutionHDG FAIL GSU 75(if installed)&GMU 44• Ensure metal objects (tool boxes, power carts, etc.) are notinterfering with the magnetometer and aircraft is not inhangar, near other buildings, parked over metal drainageculverts or on hard surfaces that may contain steelreinforcements• Ensure that a cell phone or a device using cell phonetechnology is not turned on (even in a monitoring state) inthe cabin.• Cycle power after moving aircraft away from metal objectsto determine if metal objects were the source of theinterference. Allow up to five minutes for the heading toreinitialize.• Perform a Magnetometer Interference Test to check forinterference from onboard electrical system components(e.g. NAV lights). Pay particular attention to any newelectrical devices that have been installed since the aircraftwas new. Correct any discrepancies that do not allow thistest to pass before continuing.• Ensure GSU 75 and GMU 44 connectors are secure.• Check the wiring and any inline connectors between theGSU and GMU for faults.• Recalibrate the GMU 44• Load configuration files to the PFD, GIA1, and GIA2✓ If problem persists replace the GMU 44.✓ If problem persists, replace the GSU 75.GSU 75(if installed)&GMU 44• If this message persists longer than five minutes, performAHRS calibration procedures as described in Section 7.10.
