Garmin Service Alert on GFC500 Autopilot

Has anyone received this from Garmin on their GFC-500 autopilot?

Apparently there is a pitch trim runaway with their autopilot. Please read for more details.

Scott Sherer
Wright Brothers Master Pilot, FAA Commercial Pilot
Aviation Director, Piper Owner Society Forum Moderator and Pipers Author.

Need help? Let me know!


  • Yes, my shop got it and told me he would not release the airplane for test flight's until Garmin had a solution. Kinda hard to do initial set up with all the breakers pulled.

    I own and fly a 79 PA32RT-300T. Previous aircraft are a 79 Archer and 76 Arrow.

  • Unit74, that's a bummer...hope Garmin can give you an early Christmas present.

  • I can see his point. He's not going to put a plane back in service with all new glass displays and gear that is untested or configured.

    I own and fly a 79 PA32RT-300T. Previous aircraft are a 79 Archer and 76 Arrow.

  • Just off the phone with my installers. Still a few weeks from the install being complete but she said the software is already out in the experimental realm and hope to have it to installers and dealers by the end of month. No test flights until the software upgrade completed.

    She said they are unsure of what happened and have not had any reports of malfunctions come their way.

  • Unit74, are you saying that the shop is holding your airplane hostage until Garmin has their act together? You should be able to fly with the autopilot placarded and disabled unless it is mandatory in some minimum equipment list.

  • Yes, sorta. The job is not complete but he will not allow it to leave with a complete rip and replace avionics job when the gear is not able to be tested. I can see his point. But its probably moot as G will have a fix out before he is done me thinks.

    I own and fly a 79 PA32RT-300T. Previous aircraft are a 79 Archer and 76 Arrow.

  • Correct me if I am wrong, but a Garmin Service Letter (CYA move) does not have the force of an Airworthiness Directive. In this matter due caution is warranted, but it should be your choice on disabling your AP or not. Just saying!

    John O’Leary
    Turbo Arrow IV (KRKP)
    Wright Bros. Master Pilot

  • Back on Nov 23 my avionics shop contacted me to advise of this issue. We went ahead and disabled the pitch/trim servo through my GI 275 per the STC Service Bulletin rather than pull the breaker so I could still use the recently installed GFC 500 a/p. I've used it on a few flights since and find that it still climbs/descends and captures/holds altitude well, but the 275 AI will notify me to trim up or down manually. Not having electric trim not a big deal in an Archer, but I find that the plane is not well trimmed during cruise flight with out the pitch/trim servo.

    Still waiting on the software update that's supposed to cure this, nothing as of today according to my shop.

    Anyone hear anything different?

  • I just spoke with my Garmin Tech Rep about this issue. He said as of today, the plan is to get it out before the end of the year. The software is currently sitting with the FAA for approval. Hence why the experimental aircraft already has it but certified doesn't yet.

    Also, regarding the issue at hand. This trim runaway isn't necessarily a widespread issue. I've personally installed about 40 GFC500 autopilots in almost everything they are approved for, to include in my personal PA28-140. Not once have I seen anything even close to what this fix is for. Garmin got word of it potentially happening, and was able to reproduce said issue internally. All of this led to the advisory getting published. I know these GFC500 autopilots have had their known issues but this one seems like Garmin getting ahead of it.

  • I had auto trim installed and added to my existing GFC500 just this past November. I picked up the airplane two days before the SB. On the test flight, the issue occurred instantly. As soon as A/P was activated, an uncommanded auto trim down to the hard stops occurred. My GFC500 was flawless until I upgraded. This is definitely a problem.

    Greg Arserio | PP-ASEL-Instrument | N8390C 1976 Archer II | Rochester, NY (Based at KSDC)

  • Like I stated above I've personally never seen or heard about it, that is until now. Was it just the one time or did it continue to repeat on multiple attempts?

  • Issue repeats each time A/P is engaged. At upgrade time, my GFC500 software was updated to current version. I think that is the problem… last software update included the glitch. The trim servo motor is powered two different ways depending on what is actuating it… autopilot or trim switch. Pulling trim circuit breaker doesn’t solve the problem because, per the STC, auto trim is powered via the autopilot circuit while the yoke trim switch is powered by the trim circuit breaker.

    Greg Arserio | PP-ASEL-Instrument | N8390C 1976 Archer II | Rochester, NY (Based at KSDC)

  • Greg Arserio | PP-ASEL-Instrument | N8390C 1976 Archer II | Rochester, NY (Based at KSDC)

  • Just heard from my avionics shop, Garmin's update is out for certificated planes. I'll have it installed today or tomorrow. Not expecting to notice much as I never had a runaway trim issue, but it will be nice to have that 3rd servo back!

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