AP Rolls to Right When Engaged

jsalak

I love flying!
Joined
Apr 29, 2013
Messages
31
Location
FL
Had an incident yesterday when I engaged the AP GNSS/VS mode the AC immediately rolled into a right turn despite already being on course (AC over the magenta line). I was climbing through 5,000 for the altitude bug of 6,500 on a course of 184 with a BTW of 184 and xtrk error of 0.08 nm. The only unusual part was a heading of 204 to correct for a 15-25 knot 90 deg crosswind. After a 75 deg course change I disconnected the AP and returned to on-course. I tried using the HDG/VS mode with the HDG vector matching the magenta course line and got the same right turn as soon as it engaged. I let the AP make most of a 360 deg turn to see what it would do and disconnected the AP when the bank angle got to 40 degrees with 7 deg down angle (PA=5100, Alt Bug = 6500, VS Bug=800, Speed Bug=78, IAS=112, VS=-1,100 fpm). After returning on-course at 6,500 I turned the AP off, then on and selected HDG/ALT mode and the AP appeared to operate as it should. I had flown the reciprocal route a couple of hours earlier in GNSS AP mode and had no issues with track following or Alt Bug decent (and 90 deg Xwinds of 25-35 knots). The only numbers of note in the flight data are the AP Roll Steps went from a fairly steady -26 to 0, AP Pitch Steps from 22 to 0 after I powered the AP off, then on. I have not really had any issues with the AP / IFD-540 and flying coupled RNAV GPS approaches.

Any ideas on why the AP wanted to turn into the wind when already on-course?

John Salak
RV-12 N896HS
 

GaryRay

New Member
Joined
Apr 20, 2011
Messages
16
I have similar results with my Dynon Skyview HDX and I also had it with my D10A which was 13 years old. My servo was serviced by Dynon during the install of my HDX system but nothing was reported as being wrong. The behavior still occurs and I have not had enough time to try everything to sort it out. The servo has new controller hardware.
Currently, I have no idea what is causing this behavior.
 

WmInce

Member
Joined
Jul 10, 2019
Messages
66
Suggest you perform the autopilot servo test.
If test fails, inspect the autopilot servo shear pins.
 

peter9545

I love flying!
Joined
Mar 4, 2018
Messages
21
Location
Australia
FWIW I had issues with my AP maintaining direction and implementing unnecessary turns. In the end I tracked it to a corroded connection at the servo. I remade the connections and the problem went away. In the end a relatively quick and cheap resolution.
 
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