Garmin has found a problem with the optional GSA28 auto-trim for the GFC500 autopilot which could cause runaway nose-up trim. This does NOT affect the basic GFC500 without the optional autotrim. If you have auto-trim, you must immediately disable the autopilot by pulling and collaring the c/b and placarding the autopilot inop. You can then take it to your Garmin shop to have the auto-trim disabled after which you can resume using the autopilot, manually trimming as needed when you get a TRIM light. For more information, see the documents below or contact your Garmin dealer.
Service Alert 22109 Rev A is available at:
The recommended Service Bulletin 22110 Rev A is available at:
Garmin says they'll have a permanent fix by the end of the year.