---

MAGIC EFIS Compass System Operation

Al Gialousis
Product Support Manager

Operation of the MAGIC EFIS compass system is very easy on the surface. Raw magnetic heading input data is taken from the aircraft flux gate. After an ADAHRS unit has been calibrated to a particular flux gate input, the raw data is buffered and plotted against a calibration curve. This calibrated heading data is then transmitted as label 320 on the ARINC 429 digital data bus to the Navigation and Flight Displays. The required calibration procedure is described in the system installation manual, Meggitt document # 1031234. During maneuvers, the ADAHRS calculates heading information based off rate sensors within the unit. During level flight, the ADAHRS will realign itself to the aircraft flux gate at a slew rate of 6 degrees per minute. Newly installed ADAHRS, which have not been through an initial calibration procedure, will not transmit this information until the calibration process has been completed. This will cause a heading "flagged" condition upon turn-on.

Troubleshooting:

When a problem with the displayed heading information is reported, it is not necessarily an ADAHRS failure. Like most of today's modern technologies; it can be garbage in, garbage out. Defective flux gates, along with open or shorted wiring of the windings, have caused compass systems to "drift" or "flag", giving the appearance of an ADAHRS issue.

"As a rule of thumb, the slower the rate of turn during calibration, the better."

When faced with needing to determine the cause of such reports, the following tips are offered as guidelines.

• Proper system operation is dependent upon alignment of the aircraft flux gate. Insure that the flux gate index error induced by the magnetic field of the aircraft is below 1 degree.
• Verify the integrity of the wiring between the flux gate and the ADAHRS, including cross-shorts and shorts-to-shield.
• Accomplish the calibration procedure in the time frame specified in the installation manual. As a rule of thumb, the slower the rate of turn during calibration, the better. In the event that all ground tests are satisfactory and a flight test is required to determine the system issue, a dual ADAHRS system offers the following option.
• Swap the position location of the two ADAHRS or the electrical connectors to them, if practical. If the symptom remains on the same set of displays, the ADAHRS is fine and there is an issue with the flux gate or wiring. If the symptom follows the unit to the opposite set of displays, the ADAHRS is defective.

Recent compass system problems have been reported on the Piper Malibu Meridian application. After relocation of the flux gates from the vertical to horizontal stabilizer, the dual systems have split more than 6 degrees, causing the digital heading display to give an amber comparator alert indication. After investigation, it is believed that moisture condensation at the connector for the flux gate is inducing heading system errors. Potting of the connector back shell and sealing of the connector to flux gate area has had positive results in eliminating these heading system issues.