gfc700 fail

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TJS
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gfc700 fail

Post by TJS »

I just had an interesting experience on my 100 mile IFR cross country. We arrived at the first airport, uncontrolled, did the approach to minimums and executed the missed approach. In the climb to 5000 ATC indicates a climbing left turn direct to our next destination. Still in the turn we enter cloud and the autopilot immediately disengages with a white box and read AP inside. :shock: It takes a bit to get wings level, with more than a little help from my flight instructor, and each attempt to re engage the auto pilot fails in a matter of seconds. We decide to hand fly back to our to our departure airport and we notice the left fuel indicating half full(filled 30 minutes prior). concerned we watch the fuel decrease to zero in about 15 minutes. Although it did not feel like it was empty on the left I decided burn fuel on the right only, didn't need a restart mid flight to add to the list.
Just to add to the fun we intermittently lost TAS, OAT, and Wind.
upon landing the fuel on the left was indeed full.
We switched to another aircraft and got the trip done.
My plane is now back at where the annual was completed just a week prior. :scratch:
I am not sure what to expect nor how to react to comes next.
Any thoughts, ideas and comments are welcome.
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Lou
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Re: gfc700 fail

Post by Lou »

Hi Tim,

Here's what I have learned and it may point to the solution. When I first picked up my aircraft, the fuel flow guage was not working intermittently. We went back and forth changing sensors and cleaning contacts only to have it reoccur. Finally, they swapped out the GEA 71 LRU and everything was fine.

I'm looking at the G1000 System Overview diagram and I notice that the GDC 74A is responsible for OAT, Airspeed and Altitude. The GDC 74A passes its data to the GIA63, which controls the autopilot servos, and the AHRS, which also feeds the GIA 63. I believe that if any malfunction is detected in the data, the GIA will disengage the autopilot. So the autopilot malfunction is a symptom, not a cause.

For example, I took off a few months ago after installing a terrain data update. The update sync was not finished when I took off. About 15 minutes into the flight, the autopilot disengaged. I pulled out the manual to look up the error code. It showed a failed preflight test. I surmised that it was related to the update. I asked for permission to go off frequency to cycle the panel, and when I did that it came back all good. No problems since.

These experiences tell me that a) LRU's fail selectively and b) the autopilot won't work unless all is good. Since you have issues with OAT and TAS, you may want to have a shop swap out the GDC 74A unit to see if that is the problem.

Just my CAD$.25 (about USD$.18)
TJS
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Re: gfc700 fail

Post by TJS »

Thanks, that makes a lot of sense and explains my intermittent issues. I will post the findings when we get there.
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Re: gfc700 fail

Post by TJS »

Mulling this over a bit, I have now had issues with three of the LRU s. The transponder has had intermittent issues, and now the auto pilot and the fuel sensor. Sounds like a cable or connection issue or the GIA 63W. Tech thought maybe software but that was the solution to the Transponder a couple of weeks ago. Hmmmm
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Re: gfc700 fail

Post by TJS »

:scream: it keeps getting better and better. :scratch: So far we have change a fuel probe, CHT Probe and both GIA63W ouch!!! :shock:
now I get the #2 CHT that we replaced reading 75degF high, right fuel stuck at 15gal, and now #4 egt falls off intermittently and another autopilot disconnect Not sure where to turn other than maybe a better avionics troubleshooter. :scream:
any advise?
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Re: gfc700 fail

Post by CFIDave »

These sound like connector issues. If you haven't already done this, pull all the LRUs out of the G1000 equipment bay under the rear baggage compartment, and spray the contacts of the bay with electrical contact cleaner.
Epic Aircraft E1000 GX
Former DA40XLS, DA42-VI, and DA62 owner
ATP, CFI, CFI-I, MEI
TJS
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Re: gfc700 fail

Post by TJS »

:scream: well it think i got it now,
The root cause was an intermittent transponder. Found some inferior cable that was upgraded, replaced a couple of questionable connections and voila no more failures.
well lets hope, 50hrs and counting.
Oh I almost forgot to mention the best part; $10,000 later
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Star57
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Re: gfc700 fail

Post by Star57 »

TJS wrote::scream: well it think i got it now,
The root cause was an intermittent transponder. Found some inferior cable that was upgraded, replaced a couple of questionable connections and voila no more failures.
well lets hope, 50hrs and counting.
Oh I almost forgot to mention the best part; $10,000 later
Anywhere along the way, was there any kissing before the 10k bill...?
Exactly, no kissing...sad
Welcome to GA
TJS
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Re: gfc700 fail

Post by TJS »

sadly, no extra pleasures
GA is a wonderful place to be, no shortage of surprises.
good people though.
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