I'm having problems with the auto pilot altitude hold function and need some help. On any given flight, the altitude hold will stop holding the programmed altitude after a while. Some flights it may work for 5 minutes and others it may work fine for 15 to 20 minutes. But it will always fail, resulting in the aircraft going into a steep climb. I can usually shut down the auto pilot, get the aircraft back under control and trimmed and then reset the auto pilot alt hold and it will work again for a while. I do have pitot heat turned on and have looked in the failures section and nothing is programmed to fail. The aircraft in this case is the default Lear but it also happens with the default 737.I'm running a Saitek X-45 and at one time I've had the trim assigned to either the lower rotary knob, the upper rotary knob or to the upper left hat switch on the stick. I was thinking the contacts could be dirty on the rotarys causing a problem. But it still happens with the trim assigned to the hat switch.Has anybody had this problem? Any help, hints, tips or suggestions would be greatly appreciated.ThanksDoc G

As far as I understand the elevator trim is constantly adjusted by the autopilot for altitude hold so the problem is probably caused by the main elevators. If your stick is for some reason taking unwanted control of the main elevators the autopilot will try to compensate until the trim has reached the end of its travel. So I would suspect your main elevator settings in your stick setup or perhaps the contacts need checking.

Hi Doc,Try this. Get the plane set up straight and level, enable the autopilot, then disable the joystick (I think it is either the k key or Ctrl+k). If it still happens, then you've ruled out the joystick as a problem. Let us know what happens. R-

Thanks for the suggestions guys. After configuring for straight and level flight with the auto pilot altitude hold engaged I disabled the joystick and all went well. As soon as the joystick was enabled the aircraft went into a steep climb. Disabling the stick again the aircraft would slowly return to the programmed altitude.I then paused the sim and deleted the joystick trim assignment, just going with the default keyboard assignment. In straight and level flight at the programed altitude, disabling or enabling the joystick had no effect on the flight. The aircraft would remain straight and level at the programmed altitude.At this point it looks like the stick may be causing the problems. Could be my sensitivity and null zone settings. I'll keep fooling with it.Thanks AgainDoc G

The axis you use for trim is probably "jittering" (small fluctuations that causes FS to see the axis and overuling the AP trim command).The best way: define a larger null zone around the center, and make sure that, when flying on AP, the axis is centered (i.e. within the Nullzone).Rob

Thanks Rob. I've been playing with the null zone and sensitivity settings and see some improvement. Just a case of trial and error until the correct settings are found. I try to remember to center the trim before turning on AP.Doc G