Garmin & FAA have released a notice about the potential for runaway trim in the GFC500 autopilot. It requires disabling the autotrim and autopilot until a new software release is issued.
From the notice:
”Garmin has identified an issue with GFC 500 autopilots with optional auto trim installed in certified, experimental and Light-Sport Aircraft, including certified installations installed with optional GSA 28 pitch trim in accordance with Garmin STC SA01866W. This issue may result in an uncommanded automatic trim runaway when the autopilot is first engaged. This condition could result in a sudden and significant deviation from the intended flight path.
Garmin Service Alert 22109 Revision A requires operators of certified installations to pull and collar the autopilot circuit breaker and placard the autopilot as “inoperative” prior to further flight. Operators may contact a Garmin dealer regarding reactivation of the GFC 500 autopilot with the optional pitch trim configured off in accordance with recommended service bulletin 22110 Revision A.”