TO: Dealers and Owner/Operators of Garmin G500 and G600 Systems
SUBJECT: Possible temporary loss of heading/attitude information in Garmin G500 and G600 Systems following extended power-on stall and slow flight maneuvers.
All Garmin G500 and G600 systems using GRS 77 Software version 3.00 and previous versions or GDU 620 Software version 6.20 and previous versions are affected.
Temporary loss of heading information (red-X'ed heading) can be caused by sustained (greater than 7 seconds) in-flight operation with true airspeed less than 40 knots and GPS ground speed less than 30 knots.
Additionally, it is also possible that the preceding condition can cause GRS 77 AHRS to reset, particulary if the low speed condition persists for greater than 10 seconds. In such cases, heading and attitude will not displayed on the PFD (red-X'ed) while the GRS 77 AHRS resets and realigns (typically less than one minute).
Pilots should be aware that operating in the conditions noted above (such as power-on stalls or slow flight) could result in a temporary loss of primary heading and/or primary attitude.
If heading becomes unavailable (heading red-X) and/or if the GRS 77 AHRS resets (attitude and heading red-X) in flight, refer to the standby attitude indicator and compass while the AHRS unit(s) reset and realign.
This issue will be fixed with a future software release of the GDU 620.