Ahrs Troubleshooting; Heading Red-X; Heading Failure Indication (Full-Screen Pfd) - Garmin G3X Installation Manual

20.5 AHRS Troubleshooting

20.5.1 Heading Red-X

Figure 20-4 Heading Failure Indication (Full-Screen PFD)
If a Red-X (steady or intermittent) is displayed on the heading (Figure 20-4), check the following while the
aircraft is on the ground:
1. 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, rebar). Localized sources of interference on the ground may consistently cause a Red-X to
be displayed on the heading in the same spot while taxiing, this is not caused by a failure of the
GMU 22 or its calibration.
2. When the aircraft is taxiing on the ground with a yaw rate of less than 1.5 degrees/second (i.e.,
taxiing essentially in a straight line) GPS track information is used to update heading information.
This logic is applied regardless of magnetic anomaly detection.
3. The GDU may display Red-X on the heading if the GSU 73 does not have GPS information, or if
it senses a magnetic anomaly.
4. While a magnetic anomaly is detected and the aircraft is determined to be stationary, the value of
the heading output is frozen. When either the aircraft is determined to be no longer stationary or
the magnetic anomaly ceases, heading will be unfrozen and determined as useable. In this context,
the aircraft is considered to be stationary when its yaw rate is less than 1.0 degrees/second and all
other angular rate and acceleration values are sufficiently small. (moving or shaking the wings or
tail for example can cause a Red-X to be displayed).
5. Check to see if any new equipment has been installed on the aircraft, and reference
minimum distances for installed equipment from the GMU 22 to prevent interference.
If the GMU 22 heading is not present on the GDU 37X, there may be a problem with the RS-232 or
RS-485 line between the GSU 25/73 and GMU 22. Troubleshoot any possible wiring/connector issues
before replacing either unit.
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Rev. L
G3X Installation Manual - Troubleshooting
Table 8-4 for
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