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Default Boeing 737-800 autopilot problem in flight with loss of control of aircraft


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I have taken a few years off from flight simming, but never encountered this problem before. I love flying the default Boeing 737-800. I even have the Go Flight MCPPRO for my auto pilot. When ascending at 250 KIAS, right about when I reach FL 240 I lose airspeed which rapidly drops to zero. I disengage the autopilot and every time the aircraft goes into an unrecoverable spin and dive which becomes unrecoverable. At this point I usually exit flight sim before hitting the ground. This seems to happen almost every flight and was not a problem when I was flying for a virtual airline years ago and logging many hours. Why FL 240, why nearly every flight. I am getting ready to take another long break from this if I can't figure this out. I am flying with the FS Real WX weather program. Could it be severe weather causing this to happen because of the weather program? Is this autopilot related or just the aircraft always going out of control at this altitude. Also, before this happens airspeed jumps up and down. Please help. This makes no sense to me. I have not programmed in any emergency situations to happen in flight. I should also mention that I am using Windows 10, but haven't had any issues around using it.

Ms. Dale Carlson


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Hi Dale,


Perhaps your Autothrottle Systems (Arm) Toggle switch needs to be set along with an appropriate IAS MACH speed then the Speed Button pressed, otherwise the Autothrottle will not work. You will notice that your Throttle position levers will roll back to idle, and your plane will fall from the sky. It has only a little to do with the Autopilot function CMD switch.


The N1 Take off thrust can only be set in 2D view via the N1 Rotary knob (N1 rotary does not function in VC), when set along with A/T toggle switch you will see the throttle position levers and thrust increase/decrease to the percentage set using the rotary knob. If you clicked the SPEED button or N1 Button without setting an IAS MACH speed value, or no N1 percentage set you would see the throttles immediately rollback to idle and the aircraft would stall and begin an unrecoverable drop from the sky.

Once you are at Cruise altitude you can switch to the IAS MACH SPEED setup. You can even use this in the approach phase where you wish to maintain set speed throughout your decent. You will see the throttle position levers roll back continually even to idle, or roll forward to match conditions/ configuration and set speed, to maintain the set speed. (A/T ARM = Autothrottle armed) not active unless SPEED or N1 buttons are pressed.

I would switch off A/T while in the Approach/landing phase just so that you have full control of throttle levers / Engine thrust.


Also remember that if your PITOT tubes are iced or blocked these systems will malfunction.





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Got a AlphaSim SR-71 that flies along at mach 3.5 then all of a sudden just starts a...


"unrecoverable spin and dive which becomes unrecoverable"


HMMM... icing pitot tube, that could have been it thanks for sharing the tip jethrom


...or maybe the wings became blocks of ice

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Updating the post, since the OP has not replied.


Not knowing the OP's OAT @FL240, 24000ft we may never know if the wings and engines were blocks of ice.


Hopefully this added info will be useful to someone else who loves flying the default B737-800.


Understanding the AutoThrottle A/T ARM, SPEED, IAS/MACH setting rotary, & N1 Setting rotary, and the AutoPilot CMD switch & Alt Hold are only part of the picture when flying in cold conditions. Your OAT (OutsideAirTemperature) will determine if you need to implement these functions. Or drop from the sky like a lead brick.

With regards to cold conditions at altitude, and uncontrollable aircraft fall from the sky, AntiIce Wing and Engine as well as ProbeHeat (Pitot Heat) are needed. Accessing these operational toggle switches can be done through the (2D panel Overhead Simicon) or the (2D panel cycle key "a" keyboard key).

These AntiIce function toggle switches aren't operational in the 3D VirtualCockpit Overhead Panel.

Pics below.


2D panel "a" key cycle, Pitot Probe Heat, Wing & Engine AntiIce


SimIcon 2D panel, Pitot Probe Heat, Wing & Engine AntiIce


Non functioning in 3D VC


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