hi all i was wondering if anyone has suggestions or tips, or can give me a general slap in the right direction to resolve a problem i'm having.

 

my pmdg 737 800 ngx is having problems with its auto pilot system. for example i can leave LIMC heading for EGLL, with correct SID's and STAR procedures respectively and flight plan set with speeds and altitudes correct. the problem that i have is i can be in a stable climb and or cruise, with both FD's set, auto throttle on LNAV and VNAV active with CMD A on, my joystick will suddenly pull back, the aircraft goes into a steep climb and or decent LNAV VNAV and CMD A will have turned off.

 

Once i've managed to restore sanity and a climb and managed to line up with my next waypoint, and selected the waypoint on the FMC, LNAV will operate VNAV may or may not operate, ( i will initiate a climb depending ), but CMD A will not operate again for the flight, I switch to CMD B this can overcome the problem for the auto pilot. however CMD B can also disengage when another climb or decent occurs, and i can not get CMD A or B to operate again for this flight. 

 

Incidentally both CMD A and CMD B have never operated for ILS together.

 

im using FSX se edition and ( this may be a cause of the problem, but shouldn't be ) using FSX's real time weather updates.

 

any advice or tips will be rewarded with a drink at the bar, thanks 

 

darren mansell

 

 

 

using FSX's real time weather updates.

 

Do a flight without this and report back.

Are you sure that the airplane is not receiving back pressure on the control column ? Note that it can happen due to bad calibration issues. Are you using FSUIPC for calibrating ? In any case the FMA should then show CWS P. If the control forces induced by calibration issues are strong enough, they could damage the autopilot servos and it will not engage. You can check in the CDU AICRAFT FAILURES ACTIVE. If you recycle the FDs LNAV and VNAV should come alive in the FMA in FD only though.i