Hello. I have problem with autopilot. It disengages when I press throttle down key on gamepad. what's wrong?

Hello. I have problem with autopilot. It disengages when I press throttle down key on gamepad. what's wrong?

Not familiar with the gamepad but you might want to check the assignments for each key. You may have two functions assigned to the one you are using for the throttle, such as the mixture.

In my case the autopilot disengases when I switch to the external view.

Same problem. You have the button assigned to do two jobs. Check your key assignments.

Even if this happens only with Dash8 and not with all the other planes I have?

Key assignments can be set in the mjc84.ini under [JOYSTICK_INTERFACE_ASSIGNMENTS], as well as FSX interface. That could explain why it only affects the Q400 and not other aircraft.