When AHRS Acts Up

Editorial Staff

Thursday, December 22, 2022 at 01:49 PM ET

Verified

** The new Hartzell Cessna 182 prop** Hartzell

Key Takeaways:

Multiple aircraft experienced critical in-flight failures of their Attitude and Heading Reference Systems (AHRS), leading to significant loss of primary flight instrumentation and autopilot functions.
These failures occurred in various operational contexts, including cold weather, departure, en route flight (both VMC and IMC), and during severe turbulence.
Pilots encountered symptoms such as "X'd out" displays, PFD blackouts, and loss of critical data like attitude, heading, and airspeed, often requiring reliance on backup instruments or emergency procedures.
Diagnosis of these AHRS failures was frequently challenging, with many incidents having unknown causes or no discrepancies found during subsequent troubleshooting.

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Beechcraft 58 Baron

Cold-Weather Failure

While at cruise altitude of 14,000 feet on a very cold day, the Garmin G500 panel flagged the airspeed, altitude, AIS and OAT; heading and horizon were all “X’d” out. Loss of all data from the AHARS (p/n GDC74A). Pilot used the backup instruments to complete the flight. Whenever cold, the unit would fault.

Part total time: Unknown

Beechcraft B200 Super King Air

‘Return For Repair’

On departure, red roll and pitch annunciators on both pilot and copilot PFDs illuminated. The #1 PFD then switched to AHRS #2, and then both PFDs tumbled. After 30 seconds, they turned black with red “X’s” through the EHSI and EADI, with yellow “Return Wings To Level,” “AHRS #1 needs service” and “Return For Repair” annunciations. Currently working with manufacturer to resolve issue.

Part total time: Unknown

Beechcraft B200 Super King Air

In-Flight AHRS Failure

While en route in IMC, the attitude and heading reference system (AHRS) and autopilot failed in flight. The aircraft was level at 6000 feet and 220 KIAS, and coupled to the autopilot in nav and altitude hold modes. Pilot declared an emergency, descended to VMC and returned to departure airport. Troubleshooting has not found any discrepancies at this time.

Part total time: Unknown

Diamond DA40 NG

Unknown Failure

In cruise in VMC, the G1000 NXi phase II AHRS displayed a red “X” and the autopilot disengaged. The PFD showed failed attitude and heading with the message “AHRS Align: Keep Wings Level.” The GPS operated normally. After 32 seconds, the AHRS came back online. Unable to explain the cause or what would trigger the failure.

Part total time: 285.0 hours

Pilatus PC-12/45

Turbulence-Related?

The pilot was cruising in bad weather and experienced severe turbulence. Shortly thereafter, the #1 AHRS failed, indicating a red “X” across the screen. The pilot declared an emergency and diverted. On approach, the #1 AHRS energized and operated normally throughout the rest of the flight. Subsequent ground tests of the system were all nominal, and maintenance determined there were no faults with the system.

Part total time: 642.0 hours