The FAA has posted a notice alerting operators that Garmin has issued Service Alert 22109 Revision A regarding its very popular GFC 500 digital autopilots. The notice only affects those autopilots with the optional GSA 28 pitch trim system installed, associated with Garmin’s Supplemental Type Certificate (STC) SA01866W. That configuration, approved for certified, experimental and light-sport aircraft, has an issue that “may result in an uncommanded automatic trim runaway when the autopilot is first engaged,” according to the FAA notice, which includes the understatement: “The condition could result in a sudden and significant deviation from the intended flight path.”
The FAA said Garmin is working on a software solution to the issue, expected by year-end. In the meantime, the service alert requires operators of certified aircraft with the STC “to pull and collar the autopilot circuit breaker and placard the autopilot as ‘inoperative’ prior to further flight.” The agency advises operators of certified aircraft with the STC to contact a Garmin dealer to enable reactivating the autopilot/pitch trim combination “in accordance with recommended Service Bulletin 22110 Revision A.”
Meanwhile, the FAA alerts operators of experimental and light-sport aircraft equipped with the autopilot/trim configuration to comply with Garmin Service Bulletin 22112, which requires they “update system software or disable the autopilot or trim control prior to further flight.”
A runaway trim procedure is a good idea in any case.