DFC90 Update #2

Just prior to dropping the plane off for annual, I flew it to Gardner Avionics to get the DFC90 swapped out.  This is the third unit to be installed and I was hoping that this one would work as advertised.  Due to crappy weather, I could only fly it home and didn’t get to put it though any real testing.  It seemed to be tracking well and flew with no issues.  I stopped for fuel at Enterprise and as I held short of the runway to depart, the PFD completely blanked out!  After a couple of minutes it came back on, so I carefully flew it home and put the plane away for the night.  The next day I flew it to its annual and all seem to be working.  During annual, the mechanics said it failed three times on them as well.  During this annual, I also had the mechanics completely re-rig the aircraft to make sure that it was set up properly since this might also have an effect on the autopilot.  All of this PFD failures has me thinking that the PFD has been the issue all along and not the DFC90s.

On April 2^nd, I went to pick up the plane from annual.  I did my preflight and all was well.  About five minutes after start-up while doing my checks, the PFD failed again.  Since the weather was severe clear (VFR), I carefully flew it home and called Avidyne.  The following week they sent my old PFD back (now upgraded) and the avionics shop at Dothan swapped it out.  Fingers Crossed!

Saturday April 14^thit was a beautiful day with no wind, so I took the plane up and ran it though all the autopilot testing.  Overbank, stalls, envelope protection, ILS approaches coupled, and just with flight director, all went wonderfully.  Things seemed to be working great! 

Today (April 20^th) I finally got to get the plane up and put it through some more testing to make sure the DFC90 is working.  I flew my father over to 06A (Tuskegee Field).  It was a nice day, but a little windy and a little bumpy.   The autopilot failed repeatedly blowing through heading bug settings, “servo limit” warnings constantly, unable to hold a coarse and no trim annunciation.  I did the Cirrus trim test and the plane still turned to the right like a P51 and to the left like a B747.  CRAP! 

This really puzzled us and since I just had the plane re-rigged, two different PFDs and three DFC90 boxes, I figured it would only be one of two things.  It was either my trim tabs were not adjusted correctly and were overwhelming the servos (unlikely), or a servo(s) was bad and causing the problem.  When we were about to go, I bent the right aileron trim tab down quite a bit to see if that made any difference.  Since the day I bought it, it had always been severely bent up and numerous mechanics had made mention that it seemed excessive.  Here is what I bent it to:

After touring the museum at Tuskegee Field we departed to fly home and found that the autopilot had gotten even worse.  Now regardless of what we did, the “servo limit” came on instantly every time I engaged the autopilot and now I had zero trim control to the left.  The plane would peel off to the right like a P51, but wouldn’t even bank left when I held the trim hat over to the left. 

Well the only change was the trim tab, so we landed at Dothan and I bent it back to its original high angle setting:

After a quick test flight the autopilot tracked almost perfectly and not once did I get the “servo limit” warning and it tracked every heading change perfectly.  What is baffling us both now is that we both felt that bending the tab upwards would have had the opposite effect on the aircraft, but for some reason, it fixed the issue.  Apparently having the tab bend down somehow overpowered the trim servo and wouldn’t allow it to work properly. 

After only one flight, it seems to work great now, but I’ll have to test it some more next week.  It might even need a little more bending upward, but so far it seems to be working.  Fingers crossed!!