PMDG 737 NGX Problem with LNAV and VNAV, always disconneting

[sten 0]

HelloFirst, I want to apology for my poor english.I have a very annoying problem with the LNAV and VNAV autopilot in PMDG 737-800 NGX- I set the flight plan, climb detail information etc. to FMC.- Enable the both FD and ARM the autothrottle, LNAV an VNAV before take off- Proceed take off with TO/GA, after a while about few feet above ground, the VNAV engage (button green light on), and later LNAV engage (but button light is off)- I am enable first CMD A autopilot, then LNAV- But first waypoint in SID procedure LNAV autopilot didn`t make it (LNAV disconnect), I am trying enable again LNAV but he ALWAYS disconnect after very short time (2 - 10s), VNAV follow- OK, then i fly manualy to last point of SID, again engage LNAV and VNAV, short time work, but very soon problem is repeate- later before slight turns (10°) between waypoints in cruise flight level LNAV again disconnecting.I try same flight route with same airporports and every time is a same problem (but always little different, in time especially). Once time, the LNAV and VNAV works almost fine, another time is a horrible.I`m study original flight tutorials, view many videos and this is not to be happend (i hope so).Please help, I don`t know, what I`m doing wrong.Thank YouSten.

[ctdesing 5]

do the fmc display any message after LNAV/VNAV disconnected. did you see the red warning light blinking after VNAV disconnected. do any other lateral navigation system engage.

Edited February 10, 2012 by ctdesing

[MrKen 3]

Sounds like possibly signal spikes from your yoke/stick

[sten 0]

So, i think thats problem solvedI shut down every weather addons and reinstal FSUIPC module, but problem is really in joystick. I use Logitech force3d pro with force feedback. I think this f.f. causes undesirable force to plane control , that`s why LNAV and VNAV always turn off. But I disconnect joystick and all works OK,or turn off force feedback function and all works OK:)However, In FSUIPC setting allows joystick calibration etc., maybe this is a better way, but I don`t know how yet.