GFC700 went offline

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rwtucker
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Re: GFC700 went offline

Post by rwtucker »

A new Nevada GPS NOTAM

https://www.faasafety.gov/files/notices ... visory.pdf

From experience, the range of impact is greater than shown on the chart, at least to the north of the center.
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Re: GFC700 went offline

Post by ihfanjv »

It sounds like a servo problem. Either a servo is slowly going out or there is an intermittent bad connection issue - probably the former. I flew a GFC700 DA40 that had the same issue you describe and it turned out that the elevator trim servo had to be replaced. I think there is a way to test the resistance of the servos under load to determine if they are close to going out of tolerance and close to failure. Maybe the logs from the G1000 can be pulled to see what the G1000 says failed - that would help alot.

To determine if it is a servo problem, someone told me that you can attempt to make this problem re-occur if you set the autopilot in level flight, then manually use the stick to try to climb, descend, and bank left or right. By adding additional load to the AP servos, you may be able to induce the failure and narrow down which AP servo is on the brink of failure (if it is indeed a servo problem).

Best of luck. Please let everyone know what you learn.
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Re: GFC700 went offline

Post by RC7 »

I have had this happen during cruise flight with the autopilot engaged in NAV mode. Got the disconnect and red AFCS warning. The system status page confirmed an autopilot failure. I pulled and reset the AFCS circuit breaker, and that fixed it.
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rwtucker
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Re: GFC700 went offline

Post by rwtucker »

RC7,

Yours was the exact pattern for my GFC700 but the reboot solution worked only a few times before it failed permanently. The problem was a servo. I was told by the repair center that they have replaced many defective servos of a particular revision. Garmin replaced mine with a rebuilt unit of a different revision number. Based on my experience, I would no longer put yourself in a situation where you were relying on the GFC700. I was in and out of clouds at night and 12,000 MSL over the Continental Divide when mine said goodbye (the first time).
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Re: GFC700 went offline

Post by RC7 »

Talk about bad timing! I'm not flying diamonds anymore, but I'll pass along the information about the servos to the owner of the aircraft. As far as I know, he hasn't had any issues with it since.
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Re: GFC700 went offline

Post by rwtucker »

It is only speculation as to whether these issues are related but the GPS interference map on the NOTAM I received last night appears to be more accurate than previous similar NOTAMS in that it depicts the actual range of interference I believe I have experienced in previous testing periods. It shows an extensive area of interference even at lower altitudes whereas previous NOTAMS indicated ranges like this only in the upper flight levels. The testing geocenter is also different than previous tests. Most of the previous tests were in the classified areas in Nevada.

Note that four of these seven test periods over the next month span two or more days.
UTTR_16-02_GPS_Flight_Advisory.pdf
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Kyle
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Re: GFC700 went offline

Post by Kyle »

So I had an autopilot failure tonight. I have a 2008 WAAS w/ GFC700. I was being vectored for an approach with the Autopilot engaged in HDG/ALT mode. I got the red "AFCS" annunciation on the PFD and the autopilot disconnected. The flight director continued to work.

The AFCS stayed illuminated through at least most of the approach. I noticed it was still illuminated while on short final. After landing I noticed it was no longer illuminated. Before I shutdown I did check the aux page and had green checkboxes for everything. (At this point did not have the AFCS warning though).

I went for another flight immediately after and went around the pattern a few times but did not get the annunciation again. I did engage the autopilot twice in PIT/ROL & HDG/ALT mode during this flight and had no issues.

From this and other threads, I've gathered that possible causes could be:
1. Electric trim switches on stick
2. A failing servo
3. Poor electrical connection on a module in the G1000 rack
4. Lack of GPS lock (I'm thinking unlikely, and would a GPS lock even be needed in HDG mode?)

Are there any other causes anyone has experienced?

Also, I forgot to pull the SD card, but intend to check the logs. Is there anything in particular that I can look for in the logs?
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Re: GFC700 went offline

Post by Barry »

I had a similar problem last year. Randomly the GFC700 would drop off-line. We went through every diagnostic that Garmin and my avionics guy could think of, to no avail. And then it all became clear. My alternator failed when the engine started one day. Needless to say, no flying for a few days until it could be replaced. Glad it happened on the ground and I was wishing I was in the air rather than the other way around. After the alternator was replaced the GFC-700 issue never reappeared. We suspect that that there were undetectable voltage fluctuations going on as the alternator began to fail and that caused the autopilot to drop offline randomly in conjunction with a small spike or dip. So... you might want to do a diagnostic on the alternator. Maybe coincidence, but nothing else changed and the problem did in fact disappear.

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N984ES 40.827- KEIK, Erie Colorado
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Re: GFC700 went offline

Post by ZAV »

I was descending via VS mode today with my GFC700 autopilot and got the aural alert with the red AFCS box on the PFD. Soon after that alert, the alert changed to a red PFT box. There was a data path failure alert that also showed up in the G1000 alert section.

The flight director was working normally and no other red X’s showed up. The flight controls functioned normally (except the electric trim) after the failure and disconnect. I was in and out of IMC while descending so I didn’t troubleshoot or try to pull breakers, etc.

After landing I reset the avionics and did the autopilot ground tests and everything seemed OK and the data path failure alert wasn’t there.

Is this something to worry about? Should I get it evaluated before flying again or do a flight test and see how things go?
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Re: GFC700 went offline

Post by lgrennlee »

I recently had this happen, an audio warning, red and white AP in the autopilot status databox and then the AFCS flag popped. Pressed the AP button again, no response. Visited the AUX page and confirmed that all of the devices for the AP were unavailable. I cycled the breaker and check boxes went green and everything was fine. Pretty bumpy out though that particular part of the flight wasn't so bad. The remainder of the flight was without issue. Flew for about 7 hours total that day.
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