Some Units Have Experienced Temporary Loss Of Heading And Attitude Display

The FAA has issued a Safety Alert for Operators (SAFO) alerting owners, operators, repair stations, and mechanics to the temporary loss of displayed heading and attitude in aircraft equipped with the Garmin GRS 77/77H AHRS (Attitude Heading Reference System).

Garmin has received a limited number of reports of a temporary loss of displayed heading and attitude (provided by the AHRS) by the following products: Garmin G1000, G1000H, G950, G900X, G500, G500H, G600, Cirrus Perspective, and Embraer Prodigy Integrated Flight Deck Systems. Garmin issued Service Advisory No. 1309, Revision B on April 4, 2013 advising owners and operators. Garmin continues to investigate the issue and may identify additional future action.

Two possible causes have been identified by Garmin:

1. Moving the aircraft on the ground (e.g., towing operations) during the first 10 seconds after turning on power to the AHRS (when power is applied to a primary flight display (PFD), power is also applied to the associated AHRS);
2. Magnetic interference introduced near the magnetometer(s) during AHRS initialization (i.e., during the 60 seconds following power up of the AHRS).

Either of these actions can cause a noticeably drifting heading to be displayed on the PFD prior to takeoff, which may lead to a temporary loss of PFD displayed heading and/or attitude information after takeoff and during climb.

Garmin defines “noticeably drifting heading” as when the displayed PFD heading is continuously turning in one direction at a rate of more than ½ degree per second when the aircraft is stationary.

Garmin notes that a constant heading offset on the PFD prior to aircraft movement is not an indication of this condition. This condition does not affect AHRS in-flight restart performance.

Operators using the products identified above should, as a preventative measure, not move the aircraft on the ground during the first 10 seconds after turning on the pilot’s and co-pilot’s (if present) PFD(s). Do not take off if the heading displayed on the PFD is noticeably drifting. When this occurs, powering down and reinitializing the AHRS normally resolves the condition. Observe the 10 second limitation between power up and aircraft movement.

If the conditions described in this SAFO (noticeably drifting heading while on the ground or loss of displayed heading after takeoff) are encountered, operators are asked to contact Gramin Aviation Product Support.

FMI: SAFO