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Autopilot sends plane into inverted dive


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Hey all,

 

For the second time i've experienced weird behaviour from the autopilot.

On 2 flights the AP banked to the right, inverted the plane  crashed down towards the ground.

 

This happend 2 times during my climb to cruising altitude. 

I'm following the programmed route in the FMC. Nav mode enabled. Climb via V/S set at +2000 feet/min. Speed was around 270 knots. 

Both times this happend between 20.000 and 30.000 feet. Due to the high speed this isn't a stall. 

 

The plane just starts to bank right and keeps going. Steering left doesn't work. Neither does shutting down the AP.

 

When I try to recover the plane by steering left (before it's too late), nothing happends. The plane continues to bank right, until it's inverted and goes into a dive.

I've also checked the input from my joke and rudder, but they are perfectly normal. There is no input to steer right from any device connected to my computer.

 

Other planes do not react like this. Flight model is on Modern, not Legacy. 

 

Any thoughts what might happend? Or is may this be a bug?

 

Greetings,

 

J.Giesselbach

 

 

 

 

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That is a stall. A stall is angle of attack related, not speed related. You will have seen your nose start pitching up to about 16 degrees (to the relative airflow) then it will fall out of the sky. By trying to right the aircraft you made the stall worse. There is tons of info about stall recovery on the net so maybe have a look.

 

It is also the reason there has been so much talk from real pilots about why they don't use VS on climb, they use Speed. VS on descent is OK.

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On 3/21/2021 at 6:31 AM, J.Giesselbach said:

Due to the high speed this isn't a stall. 

 

5 hours ago, Thx1137 said:

That is a stall. A stall is angle of attack related, not speed related.

 

Agree - stalls are due to angle of attack only (https://en.wikipedia.org/wiki/Angle_of_attack).  You can fly at 140 kts without stalling and 400 kts in a stall, depending on the angle of attack.  

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I have the same Problem like J.Giesselbach. Climbing to Cruise Level with a stable Speed of 250 Knots and AP set to FD, NAV and VS 2000 Ft/Min. When passing FL80 the Climb Rate suddenly goes from 2000 Ft/min to 4000 Ft/Min and the AoA rapidly grows into the Stall Status. A/C turns to the Right and goes down with an extreme Speed and negative AoA. I can not recover the Flight and A/C crashes into the Ground.  Made further 3 Flights with the same Behaviour. Is there any Solution in Sight?

Greets

Joachim

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6 hours ago, CRJ Pilot said:

Even a real 737 pilot can't fly it 😂... Quotes the systems are completely off. Worth a watch, very interesting.. 

 

https://youtu.be/45S-wM3Kmyw

That doesn't mean much though. I'm a real light aircraft pilot but that doesn't mean I have a clue.

I think I'm more inclined to believe properly type rated pilots than those that aren't.

Ah, I just looked. So he was obviously having issues so it is hardly representative of the product that works for most of us.

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6 hours ago, a350pilot said:

I have the same Problem like J.Giesselbach. Climbing to Cruise Level with a stable Speed of 250 Knots and AP set to FD, NAV and VS 2000 Ft/Min. When passing FL80 the Climb Rate suddenly goes from 2000 Ft/min to 4000 Ft/Min and the AoA rapidly grows into the Stall Status. A/C turns to the Right and goes down with an extreme Speed and negative AoA. I can not recover the Flight and A/C crashes into the Ground.  Made further 3 Flights with the same Behaviour. Is there any Solution in Sight?

Greets

Joachim

Yes there is a solution, stop using an inappropriate AP mode for climbing. I already told you what that is.

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7 hours ago, a350pilot said:

I have the same Problem like J.Giesselbach. Climbing to Cruise Level with a stable Speed of 250 Knots and AP set to FD, NAV and VS 2000 Ft/Min. When passing FL80 the Climb Rate suddenly goes from 2000 Ft/min to 4000 Ft/Min and the AoA rapidly grows into the Stall Status. A/C turns to the Right and goes down with an extreme Speed and negative AoA. I can not recover the Flight and A/C crashes into the Ground.  Made further 3 Flights with the same Behaviour. Is there any Solution in Sight?

Greets

Joachim

Never routinely use VS mode to climb at high altitude. That is potentially dangerous, as it offers no protection against high AOA and stalling. It is OK for lower altitudes, but not when you are FL200+ You should be using SPD mode with a selected airspeed typically between 250 and 290 knots, with engine power levers in the CLB detent.


You can use VS for the very last part of the climb to help level off smoothly, but not for the main part of the climb. 

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vor 15 Stunden , JRBarrett sagte:

Never routinely use VS mode to climb at high altitude. That is potentially dangerous, as it offers no protection against high AOA and stalling. It is OK for lower altitudes, but not when you are FL200+ You should be using SPD mode with a selected airspeed typically between 250 and 290 knots, with engine power levers in the CLB detent.


You can use VS for the very last part of the climb to help level off smoothly, but not for the main part of the climb. 

Thanks for the good Explanation. I will give it a try and report back.

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