Hey Guys - Not sure if this is a 737 problem or a Prepar3d issue, but in my 20  years of simming, I've never had an issue like this.  I am having an issue using Prepar3d v4.2 with the PMDG 737, and while in cruise flight, for no reason, the plane disconnects from autopilot and goes into an uncontrolled bank which is unrecoverable due to overspeed trying to correct. I've never seen this issue using FSX with the same plane, same CH Products yoke and pedals. I am not using any add-on's. Sometime's I can get a short flight in without the issue occurring, but it seems on flights >150nm the issue occurs. Running on Windows 10, Core i7-4770k, no overclock, 32g ram, GTX 1070.

I never really fly with any other plane, so not sure if this is plane or Prepar3d specific.  Also, the plane has done this even while not in auto pilot mode, and I'm not causing the plane to go into CWS mode by hitting the yoke by mistake or anything like that.

Appreciate any help as this is quite frustrating.

Thanks,
Kevin McCarthy

There is a rare problem with the NGX and its panel states, where the trim values in the saved panel file become corrupted.  Make sure you check your control surfaces during preflight. The aileron trim should be zero, the yokes centered and no spoilers up on the wing (check after engine start and before taxi)  Try to isolate the panel state you were using when the problem flight occurred.

I have had similar issue after P3D v4.2 update several times. I was able to recover though. After that one of the autopilots usually becomes unusable and I had issues with LNAV and HDG SEL so I had to revert to hands flying till things stabilize. Really weird. I disable all addons like AS, vPilot etc., just NGX. 

 

Surely PMDG wouldn't have modelled the 737 rudder system failure (a la Flight 427) as a random occurrence?   Although the NGX is a later variant, I know. 

Try starting all flights with the default P3d4 scenario, then load the NGX and a flightplan file. I've had the same problem with other 3rd party complex aircraft. My assertion if that an entry (or entries) in repeatedly saved scenario files is negatively impacting  initialization of specific aircraft variables. It may take  several minutes to an hour before the loss of control problem occurs.

I am not sure how Kevin starts his flights, I always start with default aircraft and scenery and only than load NGX with Long Turn panel state. I use only PMDG liveries. Before taxi I always check controls and I don't have failures enabled. 

Always a classic: misconfiguration of the controls. If using FSUIPC deactivated it temporarily and try again.

Thanks for the suggestions all.  When Prepar3d opens, it has the F-22 as the default aircraft.  I switch that to PMDG and then select the weather/airport.  Should I open the with the F-22 and default airport first, and then change to PMDG etc...?

I am not using any FSUIPC.  One other thing that occurs is my rudder pedals do not automatically work when I start the sim.  I an forced to unplug the USB cable and then re-plug it in to get the rudder working.  Every once in a while the rudder will disconnect and I will need to plug/unplug again (but this has never resulted in loss of control).

1 hour ago, KevMac said:

Thanks for the suggestions all.  When Prepar3d opens, it has the F-22 as the default aircraft.  I switch that to PMDG and then select the weather/airport.  Should I open the with the F-22 and default airport first, and then change to PMDG etc...?

No, no need to select the F22, simply select the PMDG or load the scenario from that screen (this is also explained in the introduction manual.

I don't think this has anything to do with FSUIPC or control calibration.  I mentioned the panel state and you didn't respond to that, what is the panel state when you start a flight that has the problem (not all flights, just the one with problem)?