Why is the aircraft diving

Hello

 

Can anyone suggest what has gone wrong.

 

I am flying a 737-800 in FSX and using FSUIPC. Have been flying and using autopilot quite happily BUT now when I activate the autopilot the plane remains level, I set the altitude at 4000ft (or any appropriate level) and then activate the Alt Hold and the plane dives.

 

Thanks

You should have the heading, altitude, and speed numbers set into the autopilot before takeoff. Do not turn on the AP or AT until you have rotated off of the runway, have the gear up and a nice climb started. I would then engage AP and AT and set all of the appropriate hold buttons...altitude, heading and speed.

Thank you and I agree with everything you have said and that is how I would usually fly. However now, as soon as I activate the Altitude Hold the plane goes into a full dive. I have spent the last 3 days checking every setting and cannot for the life of me find anything making it do this.

Thanks

You stated in your first post that you are flying using FSUIPC. Does that mean the payware version and you have used it to reprogram a joystick or key buttons?

Are you maybe "in-range" if a glideslope, and when you activate Alt Hold, you are actually getting on a GS from above?

Before you activate the Alt Hold, do you zero the trim out? I don't think that will affect the plane when activating Alt Hold, but I know it will when deactivating.

Is the VS set to a negative number when you activate? Thus, it dives before it starts to climb...

I am just trying to think of any possibility.

I think I got a brain-cramp, too...

Pat☺

as soon as I activate the Altitude Hold the plane goes into a full dive.

 

Maybe it's grasping at straws, but does the vertical speed setting have a minus sign in front of it?

 

Edit: Oops -- that's one of the things Pat asked, and I missed it on first reading. :(

+1 to Pat and Larry! Check your aircraft.cfg under the section [autopilot]

The number in RED should be this or at least positive!

 

 

[autopilot]
autopilot_available=1
flight_director_available=1
default_vertical_speed=[color="#FF0000"]1800.000000[/color]
autothrottle_available=1
autothrottle_arming_required=1
autothrottle_takeoff_ga=1
autothrottle_max_rpm=96.8
pitch_takeoff_ga= 0.000
use_no_default_pitch = 1 // 0 = Default to current pitch mode, 1 = No default pitch mode.
use_no_default_bank = 1 // 0 = Default to Wing Leveler mode, 1 = No default bank mode.
default_pitch_mode=0
default_bank_mode=0
max_pitch=10.000000
max_pitch_acceleration=1.000000
max_pitch_velocity_lo_alt=2.000000
max_pitch_velocity_hi_alt=0.300000
max_pitch_velocity_lo_alt_breakpoint= 7000.000000
max_pitch_velocity_hi_alt_breakpoint=24000.000000
max_bank=32.000000
max_bank_acceleration=1.200000
max_bank_velocity=1.500000
max_throttle_rate=0.02800
nav_proportional_control=9.000000
nav_integrator_control=0.250000
nav_derivative_control=0.000000
nav_integrator_boundary=2.500000
nav_derivative_boundary=0.000000
gs_proportional_control=9.520000
gs_integrator_control=0.260000
gs_derivative_control=0.000000
gs_integrator_boundary=0.700000
gs_derivative_boundary=0.000000
yaw_damper_gain=1.000000

If you fly at 10.000 and set 4.000 the plane will descend.

Hello

 

Can anyone suggest what has gone wrong.

 

I am flying a 737-800 in FSX and using FSUIPC. Have been flying and using autopilot quite happily BUT now when I activate the autopilot the plane remains level, I set the altitude at 4000ft (or any appropriate level) and then activate the Alt Hold and the plane dives.

 

Thanks

 

I would check that you have the barometric pressure set correctly.