Off course turns during approach

[Mir // Flightbeam 541]

Last night when approaching KDFW's 18R, a very strange issue happened. ATC cleared my approach and to expect 18R, so in the FMC I entered STAR and ILS18R. ATC then gave me vectors for approach, so I dialed 265 degrees and pressed HOLD, then pushed the knob. The aircraft turned to heading 265. Then minutes later, it turned off course to the right for no reason, after making a 40 degree right turn it then banked to make a long left turn. I turned off flight director, turned it back on and set 265 again, and the aircraft seemed like it was fighting itself, the yoke was jerking left and right but still forcing a left turn. LOC or APP was not active at all, or pressed, being 30-40 nm from the airport. After that attempt I decided to manually land, which worked fine. I have a feeling this may or may not be the aircraft causing this, because I've had similar issues with other aircrafts, such as the airbus x which pointed upwards after capturing the localizer. Any ideas?Amir Salehi

[Matt2218 4]

Amir;If I read your post right, it sounds like you were initially following a route with LNAV, and then hit the 'heading hold' button when ATC gave you vectors?I don't know if it is causing your problem, but the 'heading hold' button tells the AP to maintain the heading you were on when you pressed it, not necessarily the heading listed in the 'heading select window'. To follow that number you need to press the 'select' button in the middle of the heading select knob. On your PFD you should see a HDG SEL flag if you've done that right. Then you can change the heading in the heading select window and the AP should follow it. This is different from how default FSX aircraft work.Sorry if you already knew this, I figured it was a place to start. Good luck!

[deltatec 0]

I have had this problem also, both on departure and approach. I have 300+hours on the aircraft most recent on Vatsim so am familiar with operation of the aircraft. d I have only encountered the problem recently. The MCP ignores all settings and does its own thing (had this with altitude settings descending from cruise as well). Have been able to rectify by disengaging autopilot for a couple of minutes then re-engaging. A work around but not a solution.I have started resetting the Panel State at beginning of each flight to see if that helps.Kevin Kyle

[Mir // Flightbeam 541]

Thanks for the tip Matt, that was one issue, but turns out it still happens. Happened again last time, except this time I watched to see what it was trying to do. My heading was 025, and ATC instructed me to turn to 340. Instead of making a short left turn, it actually turned RIGHT all the way to 340. I also had this happen to me on the MD-11F. I'm dialing the knob the correct direction as well, from 025 to 340 turning left. Any ideas why this is happening?Amir Salehi