Hi,
I was flying some weeks ago (Cirrus SR22 G2 with Avidyne PFD and DFC90 autopilot) ; everything working OK in a climb using Auto Pilot while Autopilot went off with the normal loud beeps having this message in the PFD:
https://global.discourse-cdn.com/copa/original/3X/9/1/9176121d6c993b4d0c9b7a12c155c3d4a2e06d8f.png
The preflight had been OK and the autopilot had engaged normally.
The PFD didn’t seem to fail. Everything kept working OK… it’s just like the Autopilot lost connection with the PFD AHRS data (DFC90 relies on the AHRS information from the PFD so if that is missing, the autopilot becomes unavailable), as the AHRS in the PFD was working OK: I tested that using the secondary analog instruments. Also, no red crosses or other messages. Just that AUTOPILOT INOP AHRS FAIL that is a direct message from the DFC90.
I cancelled my IR flight (it was a IR training session) and we went back to my home airfield… I turned everything off… restarted avionics… but even though the AHRS finished calibration normally, the message was still there so we couldn’t resume the flight.
I have access to a spare Avidyne PFD wich I asked to be installed in order to test everything some days later. After replacing the PFD, the failure didn’t occur so although at first it may look as it is a PFD problem, I have read similar issues in the Cirrus forum related to interferences and other components involved in this problem (like the magnetometer).
(Since then, problem has ocurred twice with one PFD, it never arises with the other)
First step will be performing a Magnetometer recalibration (that is a software thing to be done in the PFD, I have not re-calibrated yet after the issue) but I am a bit lost after that… Any suggestions on how to diagnose if it does not solve it? I have the feeling that the PFD is OK and sending it to Avidyne USA will not solve the problem. (At will be very costy).
(And yes… Avidyne dealers here have no clue about the problem. They will just suggest packing the PFD, charging 600€ for that, and sending it to USA)
Thanks!
That’s a pain.
I have the same setup as you combined with 2 × IFD440.
I don’t have any new information to help you. I can only share my own experience with you so you can compare notes.
Again, I’m pretty sure I’m not telling anything new… I hope you manage to find out without spending a small fortune. I’ve got the Avidyne insurance for situations like this.
That “order” does not surprise me. I have the SG102 AHRS (actually have done a lot of work with this box, having repaired a couple for ARINC429 development purposes) and if it isn’t sitting quite still during startup, the software gets into a mess from which it may never exit. See the “avionics internals” thread for more fun 
@Peter, the “Avionics internals” thread should receive a Grade 2 listed status :) I didn’t know about its existence until you mentioned it. It’s such a fascinating thread.
Your SG102 photos/post are really interesting. The EX5000 PFD displays a message asking the pilot not to taxi until the process is complete. I’m starting to understand why now.
Yes; the AHRS boxes use a classic 3D navigation approach, dating back to the Polaris missile, 1950s. 3 yaw gyros and 3 accelerometers, and you feed all this into an algorithm which produces various outputs like pitch, roll, and heading stabilisation for the fluxgate. High grade (low drift) versions (using fibre optic gyros, or mechanical gyros) give you full navigation in 3D by integrating acceleration to get velocity and then integrating it again to get distance. You can get really weird effects with these boxes if you move them too soon after startup, or even after startup if you move them “too fast”. Or move them in a way which confuses the algorithm.
The box outputs a “valid” signal after a warmup (some minutes) and it looks like whatever it is feeding is not able to deal with that being invalid if the aircraft is being moved.
Avidyne do a terrific warranty – for my R9 it was about 5k for three years. Worth every penny. I’d highly recommend it.
Well it works very well for me, but I guess I’m an anathema then. I like stuff to work when I want it to, and when it doesn’t I like others to fix it rapidly. It depends how you value your time.
