Autopilot Issue Videos

Here are two examples of blowing through the heading bug with the DFC90 autopilot.

DFC90 Update

So after flying the DFC90 a bit more, I have noticed a couple of pretty significant glitches.  The first one is that I keep getting an intermittent “Servo Limit” warning on the PFD.  It seems that when this happens, the AP seems to get stupid.  Typically it is when I try to fly the plane on the heading mode and then the aircraft will either fail to turn, turn slowly, or turn very aggressively and then blow through the heading bug setting.  This has also happened a few times in NAV mode as well.

The next issue is the uncoupled envelope protection.  I have stalled the aircraft, I have dived the aircraft and I have over banked the aircraft.  Only twice have I been able to get any warning.  One time was an overbank and the second time was while flying with the Flight Director and as I reached short final I got an “Underspeed” warning.

The last issue is the Flight Director itself.  It doesn’t work!  I have tried to hand fly three different ILS approaches and the Flight Director is so far off that I am not even legal if I tried to follow it.  Very disappointed!

I called Avidyne and Gardner Avionics and the answer they are giving me is that it’s the servos on the airplane, not the autopilot.

I posted this issue on COPA and Dave from Nexair told me to not swap anything out until someone that knew how to check the rigging flew the aircraft.  Then he said he was coming to Montgomery, so I fly up on Saturday and met him.  He has installed a bunch of these autopilots in Cirrus and knows the workings of them very well.  We took the aircraft for a test flight and he determined three things.  Servos are fine, Autopilot is bad and the rigging on the aircraft was WAY out of spec!  One of the tests he performed was the setting of the servo.  He would hold the trim all the way to the right, but keep the plane straight and level.  Then let go.  It is supposed to take 4-6 seconds to reach a standard rate turn.  My aircraft peeled off like a P-51 in three seconds to the right.  Next we did it to the left.  To the left my aircraft banked like it was on a Sunday stroll in about eight seconds.  You could also see it on the ground when he put in full deflection left and right that they weren’t even close to being set up the same.  Once we landed he called the VP of Avidyne and got them understanding the issue, so now all I have to do is get my avionics shop to call Avidyne and call Dave and get it fixed.  Fingers crossed!

RNAV (GPS) RW18 Dothan

Here is my first attempt at videoing an approach.  This was shot yesterday when I was testing the new DFC90 autopilot that I had just installed.  It is a very precise autopilot and even with pretty decent winds, it tracked the course very well.  Much better than the STec 55X!

DFC90 Flight Test

Today I took the plane up for 2.6 hours to do some flight testing of the new autopilot.  This autopilot is capable of many things; however here is the list of things I tested during this flight:

·         Take Off Settings – AP set armed but not active

·         Flight Director on and Vertical Speed set to 1000 FPM climb

·         Turn to assigned heading (070), switch to Indicated Air Speed Mode (IAS) (115 knots Indicated)

·         Straight and Level – Put aircraft into an unusual attitude and push S&L Button

·         Underspeed Protection  

§  Stall aircraft COUPLED – “Speed protection active” should engage

§  Stall aircraft UNCOUPLED – “Caution underspeed” should be announced

·         Overspeed Protection

§  Dive aircraft COUPLED - “Speed protection active” should engage

§  Dive aircraft UNCOUPLED – “Caution overspeed” ” should be announced

·         Test Bank Angle

§  Exceed bank limit – “Caution, excessive bank” should be announced

·         Course Intercept – Set up a 90 degree intercept (V-Airway).    Fly heading mode and GPSS steering should allow a smooth intercept of the navigation course line

·         Test automatic Baro Setting – Fly level AP COUPLED and change Baro settings.  Should automatically adjust altitude with pressure changes

·         IAS - Set 88 knots for best glide and cut power.  Aircraft should set up for 88 knots and stay there

·         RNAV (GPS) Approach with published miss and hold.

·         ILS Approach, both coupled and by hand with flight director.

Before I could even start my testing, the weather was quickly deteriorating.  At the time of take-off, Dothan’s weather was MVFR, 5-mile visibility with mist and a broken layer at 1800’, overcast at 11,000.  I departed in the rain and headed to the south east, where several airports were still showing VFR.  To the west a front was moving in and bringing with it lots of rain.  Just south of the field, the weather was VFR, so I did some maneuver work to test the S&L button and envelope protection.  All worked as advertised and the S&L button is a really amazing feature!  The one thing that didn’t work was the uncoupled envelope protection.  I tried this several times and even confirmed that my software was update, so it must be a setting that needs to be turned on.  Next I set up a flight plan and did some 90 degree interception work.  As advertised, the DFC90 interception and turned onto the course with no issues. 

After about an hour of flying, the DFC90 started to have some issues.  After two successful attempts to intercept a course, the heading feature stopped working or at best barely worked.  The PFD started to show a yellow message stating SERVO LIMIT and the plane would barely begin turning.  I disconnected the AP and tried to re-engage, but got similar results.  On a couple of attempts, it would slowly begin to turn and then completely overshoot the heading and just keep on turning.  I decided to change it up and try something else to see what it would do.  I changed my GPS to a close by airport and programmed in an RNAV approach.  The AP did as commanded and all seemed to be fine.  I’m not sure if something wasn’t programmed correctly or what, but from that point on, everything worked great.

Since the weather was quickly deteriorating, I called Cairns Approach and filed IFR and asked for the RNAV (GPS18) approach into Dothan with an initial fix of IKIQU.  This approach was done completely coupled and the DFC90 executed it perfectly!  I even tried the IAS mode set at 100 knots and it all worked great.  The approach was picture perfect with a breakout at minimums.  AWESOME!  After going missed, I flew to the hold and hoped that maybe my non-WAAS G430s would now be able to fly the hold, but unfortunately that is not the case.  I entered the hold in a teardrop fashion and flew the hold using the heading bug. 

After a few turns, I asked for vectors to the ILS from the east.  This approach went very well also.  I allowed the DFC90 to fly it coupled and it intercepted the final approach coarse perfectly, as well as the glide slope and tracked it all the way down until we broke out of the clouds at 500’ AGL.  The next approach was vectors back to the RNAV (GPS18) again with similar results.  The final approach was for vectors from the west to the ILS RW14 and I hand flew this approach using only the Flight Director for guidance.  This approach didn’t go as well, since it seemed like the FD was slow to react, so I just followed the needles to get me though the clouds.  I’m not sure if it was the FD or if maybe I didn’t have something set up correctly, so I can’t say if the FD was having issues or not.  I guess I’ll have to go out and try that one again. 

Overall, I am extremely happy with the performance of the new DFC90.  I did have a few glitches, but I’m not sure that it is anything to worry about at this time.  I really like the preciseness of the unit as well as the envelope protection.  It just provides my Cirrus with even more safety features that make me love my Cirrus all that much more. 

DFC90 Autopilot Upgrade

One of my biggest gripes with my Cirrus, was the autopilots inability to track straight on any sort of navigational aide, especially an ILS.  Especially if it was windy or even gusty, the S-Tec 55X was incapable of accurately intercepting or tracking these signals and would wander back and forth, back and forth, back and forth.  Now there is an option that will not only provide digital preciseness, but also add more safety to boot!

The Avidyne DFC90 was released a little over a year ago with the primary flight ship being the Cirrus SR2X.  They marketed this autopilot directly at the S-Tec 55X in hopes to lure a fairly large market of aircraft owners to upgrade to a far superior and safer autopilot.

The Avidyne DFC90 is an attitude based autopilot, whereas the S-Tec it replaces is rate based.  The DFC90 follows the attitude indicator and the AHRS.  Rate based autopilots like the S-Tec, use a turn coordinator for reference.  This makes the DFC90 extremely precise and far more accurate than the S-Tec.  Turns are exactly standard rate, intercepts are way more precise, level offs from climbs and descents are also much more smooth and right on target.  The DFC90 flies approaches beautifully, and extremely precise.  An ILS approach is flown straight and true all the way to minimums.  No more back and forth drunken sailor effect like the S-Tec did.   It now truly flies like it’s on rails!

In addition to the increase preciseness of the DFC90, Avidyne incorporated its “Envelope Protection.”  One of the major safety issues using the S-Tec, is that you could stall the aircraft with the autopilot.  There have been several accidents in the Cirrus fleet alone, where pilots get busy and aren’t monitoring the aircraft and the aircraft is set up to climb at a rate in which it cannot keep up with.  The end result is that the autopilot flies the plane into an autopilot induced stall.  The envelope protection of the DFC90 eliminates this issue.  If you command a climb that the aircraft is not capable of, the autopilot will allow the climb until the airspeed bleeds off and then the autopilot will hold a safe speed, not allowing a stall.  When this takes place, a voice will sound off in the headsets stating “Speed Protection Active.”  The same applies on the over speed side if you command a vertical decent that would result in exceeding Vne, the DFC90 will intervene and not allow an over speed to occur.  

Another one of the major improvements of this system is the “Straight and Level” button.  This is a great safety feature for a pilot who might be in IMC or flying at night and become disoriented and put the plane into an unusual attitude.  If the pilot becomes disoriented, all he has to do is push this button and it will bring the plane back to straight and level.

The DFC90 is a VAST improvement over the S-Tec 55X autopilot. This upgrade gives Garmin Perspective precision to your Avidyne Entegra plane at a significantly lower cost.  If you own an older S-Tec 55X autopilot, I highly recommend you upgrade to the DFC90.  It is the best money spent on an upgrade for your Cirrus!