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New DFC90 disconnects in Cruise

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GYORC View Drop Down
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    Posted: 03 Oct 2013 at 5:09am
My Cirrus Serice Center installed the complete "Panel Overmake" package into my 2006 SR22-G2 this June. Overhauied PFD/MFD, DFC90, Flap Wire, all the latest software

For the first 40 hours it worked nicely and was reliable.

Now, two days ago on an IFR flight through Germany in FL90 after the first 45 minutes the A/P disconnected itself without a warning. No other message or error message, only: "Autopilot Disconnected", of course with the beeps that come with it.

Ten minutes later this happened again, then the next time after 3 minutes, 2 minutes ... in the end it only worked in uncoupled FD mode.

On a second 90 minute flight on the same day it worked again, did not disconnect.

I let the Cirrus service Center measure the servos and they said that the  3.5 volts in the roll servos are "okay" (which i doubt). They said that they cannot do more than that and that I should "observe" the AP ... (they did not say if i should observe it it in VMC or IMC !)

On the flight home it happened again: Disconnected in IMC three times in sequence, no other error message than "Autopilot Disconnected".

After hand flying for 10 minutes I switched it on again and it worked for the remainder of the flight.

I also got an eMail from my Service Center in the UK that I should check the aileron trim tab setting and that this could be the reason especially in strong crosswinds. I did have crosswind up to 35 knots at altitude but i have a hard time believing this can be the reason.

The DFC is under warranty but nobody has really told me what to do until now.

Any Ideas, information, tips?




Edited by GYORC - 03 Oct 2013 at 3:48pm
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AviJake View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AviJake Quote  Post ReplyReply Direct Link To This Post Posted: 03 Oct 2013 at 10:42am
Two ideas:

1.  The max startup voltage for the pitch servo is 3 VDC.  The max startup voltage for the pitch trim motor is 5 VDC.  Those are the upper end limits and a healthy servo is 1-2 volts below those numbers.    Note that we have no experience with out-of-spec startup voltage servos resulting in autopilot disconnects in flight.

2.  Virtually without exception, all reports of autopilot disconnects have been traced back to poor tray connections (typically the autopilot doesn't seat perfectly well in the tray).  In some cases, the existing STec tray was unable to get to reliably connect and the replacement Avidyne tray completely resolved the problem.

As for the theories about aileron trim tab settings - I can't conceive of a reason that would result in an autopilot disconnect.  It could result in poor tracking performance but not a disconnect per design.

Are you getting the disconnect tones in your headset when the autopilot disconnects?  Depending on your answer there, there may be some suspicion with the disconnect button/signal/wire.  Doubtful but possible.
Steve Jacobson
sjacobson@avidyne.com
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Post Options Post Options   Thanks (0) Thanks(0)   Quote GYORC Quote  Post ReplyReply Direct Link To This Post Posted: 03 Oct 2013 at 10:48am
Hi, thanks for the quick answer
- the servos were tested by the Cirrus Service Center and I think they measured 3.5 Volts at the Roll Servo. They said that that's okay (..). They also measured the pitch servo and said it's ok.
- It has nothing to do with the tray I think. We took it out and put it back in again (as Aaron recommened)... and it also worked perfectly for the first 40 hours
- The trim tab idea came from the Cirrus SC in the UK that has installed the autopilot (RGV, Alec Vincent). So i don't have to test that? The TRACKING PERFORMANCE IS PERFECT!
- Yes, the normal disconnect tone in the headset and the yellow message on the PFD "Autopilot Disconnected"

I had a "Servo Limit" message maybe twice for a second or two in the last two weeks, but really only a second or so


Edited by GYORC - 03 Oct 2013 at 10:49am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote GYORC Quote  Post ReplyReply Direct Link To This Post Posted: 03 Oct 2013 at 10:50am
What I would like to know: If Avidyne says that it's probably the roll servon and I let Avionik Straubing install a new roll servo - how is this scenario covered by the Warranty in case we find out it was NOT the servo? Nobody gave me an answer to that yet ...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AviJake Quote  Post ReplyReply Direct Link To This Post Posted: 03 Oct 2013 at 10:53am
I'll go check on the roll servo installation and warranty question with Customer Service guys.  I suspect they'll send you a direct note in response but let me go check with them now.
Steve Jacobson
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Post Options Post Options   Thanks (0) Thanks(0)   Quote GYORC Quote  Post ReplyReply Direct Link To This Post Posted: 03 Oct 2013 at 12:02pm
Thank you VERY much!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AviJake Quote  Post ReplyReply Direct Link To This Post Posted: 04 Oct 2013 at 9:12am
Have you gotten a call/email from Avidyne Customer Service to resolve your question?
Steve Jacobson
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Post Options Post Options   Thanks (0) Thanks(0)   Quote GYORC Quote  Post ReplyReply Direct Link To This Post Posted: 04 Oct 2013 at 9:41am
No, i have not.
At the moment i am pretty sure that it's the roll servo... but what if not!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote achimha Quote  Post ReplyReply Direct Link To This Post Posted: 04 Oct 2013 at 10:48am
BTW, why does Avidyne not let its partners read out the DFC90 error log? I suppose the device will store the reason for such a disconnect in a non volatile memory area which can be read out.

With a King KFC, I can connect a laptop through RS232 and dump the error log. I think my dealer should be able to do that with the DFC90, too. Mine was sent from Germany to Boston to read out the error log which costed money (not mine to be fair) and time (that was mine) for nothing.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote GYORC Quote  Post ReplyReply Direct Link To This Post Posted: 04 Oct 2013 at 11:52am
I just got this information on COPA:

>>>

I strongly suggest that you replace the S-TEC 55X's tray/backplate with Avidyne's much improved DFC 90.   It's not cheap (about $500), but it solved the spontaneous autopilot disconnect problems that we were saw a couple of times on the test flight on our SR22 after our upgrade.

The S-TEC 55X's is quite simply he most poorly engineered avionics tray known to man. Under ideal circumstances, the pins have at best only 1/16" of an inch of mating... which is quite scary. Avidyne's DFC90 rack improves this.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote GYORC Quote  Post ReplyReply Direct Link To This Post Posted: 06 Oct 2013 at 7:15am
Customer service has not contacted me so far. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote GYORC Quote  Post ReplyReply Direct Link To This Post Posted: 21 Nov 2013 at 6:00am
I have written two eMails about my A/P disconnects in cruise and a possible exchange of the A/P (which is 4 months old) to Avidyne, no feedback so far. I ahd NO electrical failure so the disconnects should not be related to the condition described in the new service letter.

Who should I contact?
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