Garmin GFC 500 Manual Pitch Trim Servo Failure
I recently had a manual pitch trim failure with my Garmin GFC 500 Autopilot. Below is an email I sent Garmin that details the problem. I would be interested to know if anyone else has experienced a similar AP failure. Thanks Nick
To whom it may concern:
Over the past couple of years I’ve been upgrading the avionics in my Piper Saratoga (N8172P) to all Garmin products. I started with the GTN 750 and GTX345, then soon after added two G5’s. At the beginning of last year I had the GFC500 autopilot installed and have been, up to this point, overwhelmingly satisfied with all.
Last weekend I was flying a departure out of an airport in Miami in instrument conditions. Soon after activating the autopilot I got a PTRIM failure annunciation and the autopilot disconnected. At first the messages were “Not receiving RS 232 data” and “Not receiving ARINC 429 data”. I hand flew the airplane through the climb and the clouds until we were in visual conditions. Then I attempted to diagnose the problem. I first thought that the navigator may have lost GPS signal.
About an hour after the failure, I again engaged the autopilot in pitch and roll mode; It held. I cycled through the rest of the autopilot modes and everything seemed to function. I disconnected the autopilot to test the manual electric trim. It worked intermittently.
The next day I ground tested the manual electric pitch trim. I got the following faults: “servo hardware fault” and “servo power supply fault” and the trim servo never activated. Finally, I opened the access panel to the manual electric trim servo to see the integrity of the wiring connection. It appeared to be well seated. I also checked the function of the pitch trim wheel which was also fine. I powered up the airplane and the servo LED indicated steady red. Based on table 36-1 of the installation manual a steady red LED means the servo is not longer functioning.
I called Spaceport Avionics, who were the installers of the autopilot. I told them the story and they said they would reach out to Garmin for a replacement servo. Yesterday I spoke to them and they said that I would have to pay $400 for the replacement servo plus the cost of installation because it was out of warranty. They also told me that the warranty period started at the time of shipment, not when the equipment goes into service. Of course I was disappointed. It doesn’t seem right that a significant component like a pitch trim servo should fail with less than 25 hours of service time and on top of that I’m expected to pay for its replacement. This is inconsistent with my experience with all the other garmin products I’ve purchased. My hope is that you will aid me in coming up with a permanent no cost solution to my problem. Thank you for your consideration in this matter."**
Comments
Nick,
Sorry to hear about your issue with the pitch trim failing. Back in the analog days, electric trim failures sometimes were caused by seizing of either the drive motor or the electromagnetic clutch. However, most I troubleshot were the result of insufficient tension in trim cable itself that prevented the servo from developing the traction it required to operate. But your servo has an embedded microprocessor with built-in self test, and it's that self-test that determined and annunciated the fault. So the question is: why does the self-test "think" it's failing? If someone can identify the answer, then you should be able to arrive at a permanent solution to the problem. I worry the servo will be replaced with a factory new unit, but your problem will persist because the root cause was never identified. If I had spent 10s of K on this new installation, I'd be pretty upset if the shop and the factory couldn't fix it in short order, and at no cost to me.
If you have some free time and feel adventurous, you might request a free copy of Garmin 190-02291-01, turn to the chapter on electric trim troubleshooting, and work through the checklist with your A&P. There's additional fault information stored in the microprocessor that can be extracted by your dealer.
Good luck!
Bob
But we did discover that both the pitch trim and pitch servo
Are not functioning. (see attached pictures)
Garmin has agreed to replace both servos and cover the cost of labor. But I’m concerned that this may not be a permanent solution!
Nick, congratulations!
I share your concern; Garmin's distribution chain is so opaque you may never know the real issue, or whether or not it will reappear later.
Suggestion - send a letter to Min Kao and describe your situation and commitment to his products. Ask him to perform a teardown on the servos and report back on the results. He strikes me as someone who cares about the company and his customers a lot, and he'll probably follow through. He may also improve the product so the rest of us don't have to deal with it. A Garmin autopilot is definitely on my wish list!
True story: about 20 years ago I walked by a downtown Mitsubishi dealership and saw a Spyder parked under the bright lights. Nice looking car, but what really sold me was the Infinity sound system. After a minute of listening to Stravinsky, I reached for my checkbook.
A year later the sound system swallowed one of my CDs; it wouldn't play it and wouldn't spit it back out. The dealer replaced it under warranty, and the repair invoice showed paid, in the amount of $1700! For a CD player?
It happened again at the end of year two, and again it was replaced under warranty. Unfortunately the third failure was at 38 months, right after the warranty expired. The cost of the repair was now $1850 and it wasn't happening if I didn't pay for it. So I complained to Infinity/JBL and Mitsubishi. Both ignored my letters.
On a lark I called up an old classmate who worked for Bose, to see if he had any ideas. "Bring it up, and I'll take a look." As he and his tech opened my CD player, a big smile spread across both their faces. "Clarion!"
As they explained, in the early days of CD players only Sony and Phillips made the disc handling mechanism, and they charged a premium to any OEMs building sound systems. Then Clarion came out with a third-party solution for 1/4 the cost, and became the new supplier of choice. Problem was, their rack mechanism was not "self wiping," and after a few hundred plays all the grease dissipated and the rack seized. How did Bose know all this? Well, of course they jumped on the Clarion bandwagon too, and because of their "no questions asked" repair policy, they had a warehouse full of millions of dollars worth of scrapped Clarion units. Sometimes saving a little now costs a lot in the long run. My bet is Garmin is a lot more like Bose that Mitsubishi.
Anyway, the tech taught me how to clean and grease the rack, and that procedure became part of the annual maintenance on the Spyder for the rest of the time I owned it.
Bob