6 ms·

> One pilot has to move all focus to it, without touching the other controls. And even that may not be enough. It's quite plausibly physically impossible if t

> One pilot has to move all focus to it, without touching the other controls. And even that may not be enough. It's quite plausibly physically impossible if the pilot happens to be less strong than this one, or if the aircraft's situation is worse than this simulator's. In particular, the Ethiopian flight was in extreme overspeed (if I recall, past the max safe structural speed for the plane!), which increases all of these forces. I'm not sure whether that was being modeled by the simulator, or if the simulation's model of trim wheel force is a correct one. There's certainly no guarantee that a pilot can produce the force required to relieve aerodynamic load on the stabilizer here. It's a purely mechanical system.

_ph_ 7y ago
Actually, in earlier flight manuals for the 737 there was a description for the so called roller-coster-maneuver for exactly the case that the trim was so far off that it couldn't be operated manually any more. The maneuver consisted of pushing the yoke forward to take the pressure off the stabilizer and quickly trim back and then put the nose up again. So it was documented, that in certain conditions the forces could be too high for the pilots.
- lmilcin 7y ago
  Think of it for a sec. Your plane tries to kill you by pointing the nose down. With all your force you are barely able to make it only loose the altitude slowly. Now, would you point your nose down knowing that you may not be able to point it back up again?
  - _ph_ 7y ago
    Well, the roller-coster maneuver assumes you are high enough up that you can trade off some of your height for correcting the trim. Here is a link to the description: http://www.b737.org.uk/runawaystab.htm#rc http://www.b737.org.uk/runawaystab.htm#rc This obviously wouldn't work in cases like the Ethiopian, where the plane had very little height over ground due to the high mountains around the airport. Edit: the point isn't that the maneuver had prevented the accident, but that its existance in the flight manuals shows that it was known that the trim forces could be higher than what the pilots could apply to the trim wheels.
    - lmilcin 7y ago
      I'm not a pilot but I do sail some and the same manouver is used. You know, sails also generate huge forces which might not be possible to physically counter. What you do is, if you want to trim and are courteous to your crew, you point your yacht upwind for a moment to let them trim and then get back on your course.
      - _ph_ 7y ago
        I also did a bit of sailing and remember it was also standard to steer a bit more upwind if the boat is listing too much. That is, if there isn't anything in the way, if you steer more upwind :p
        lmilcin 7y ago
        This will actually depend on your course with regards to wind. There will be a course that will generate maximum heeling moment.
        odonnellryan 7y ago
        Generally you'll heel over the closer you are into wind while your sails aren't luffing. Taking off the wind will make the boat heel less.
    - cjbprime 7y ago
      Yeah, and I think MCAS ended up fully deflecting the stabilizer on Ethiopian. Even with a somewhat more reasonable altitude, I wonder how long it takes to physically manually retrim from one end of the jackscrew to level flight. I think even the electric motor takes at least six seconds to do that.
      - _ph_ 7y ago
        From what I read the situation was made worse by the fact that they where flying a bit on the fast side even when they were not going down yet, increasing the load on the stabilizer.
  - cjbprime 7y ago
    A normal person wouldn't, but you're probably overstating the reluctance an actual pilot would have. Being reluctant to push the nose down when in a bad situation would cause pilots of any aircraft to fail their first hour of stall training. It's more worrying that, since the procedure was removed from manuals and training, the pilots might simply not have realized that it would help.
deleted 7y ago
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JshWright 7y ago
At least some simulators are capable of modelling those forces (I don't have any knowledge of the domain, but I would assume it's standard in "professional" simulators): https://www.youtube.com/watch?v=aoNOVlxJmow https://www.youtube.com/watch?v=aoNOVlxJmow
inferiorhuman 7y ago
In particular, the Ethiopian flight was in extreme overspeed (if I recall, past the max safe structural speed for the plane!) While the Ethiopian crew did have the overspeed warning going off, it was well below the "do not exceed" and "max dive" speeds. I'm not sure whether that was being modeled by the simulator, or if the simulation's model of trim wheel force is a correct one. It wasn't. Boeing's already admitted that their simulators don't correctly emulate the forces on the trim wheel.
- salawat 7y ago
  The borked AoA vane also meant the computer was not calculating airspeed correctly. They were in an Airspeed Unreliable situation, which warrants being generous with power based on the stage of flight. Climb-out from Adis Ababa (a hot and high airport) means you've got precious little excess in terms of sacrificial power to begin with. The MAX 8 could only take-off at all due to an unusually long runway as I recall.
jacquesm 7y ago
> It's quite plausibly physically impossible if the pilot happens to be less strong than this one, or if the aircraft's situation is worse than this simulator's. That simulation would have ended in a crash if they didn't abort it. So the pilots strength did not seem to matter and the situation was about as bad as it gets.

_ph_ 7y ago

Actually, in earlier flight manuals for the 737 there was a description for the so called roller-coster-maneuver for exactly the case that the trim was so far off that it couldn't be operated manually any more. The maneuver consisted of pushing the yoke forward to take the pressure off the stabilizer and quickly trim back and then put the nose up again. So it was documented, that in certain conditions the forces could be too high for the pilots.

lmilcin 7y ago
Think of it for a sec. Your plane tries to kill you by pointing the nose down. With all your force you are barely able to make it only loose the altitude slowly. Now, would you point your nose down knowing that you may not be able to point it back up again?
- _ph_ 7y ago
  Well, the roller-coster maneuver assumes you are high enough up that you can trade off some of your height for correcting the trim. Here is a link to the description: http://www.b737.org.uk/runawaystab.htm#rc http://www.b737.org.uk/runawaystab.htm#rc This obviously wouldn't work in cases like the Ethiopian, where the plane had very little height over ground due to the high mountains around the airport. Edit: the point isn't that the maneuver had prevented the accident, but that its existance in the flight manuals shows that it was known that the trim forces could be higher than what the pilots could apply to the trim wheels.
  - lmilcin 7y ago
    I'm not a pilot but I do sail some and the same manouver is used. You know, sails also generate huge forces which might not be possible to physically counter. What you do is, if you want to trim and are courteous to your crew, you point your yacht upwind for a moment to let them trim and then get back on your course.
    - _ph_ 7y ago
      I also did a bit of sailing and remember it was also standard to steer a bit more upwind if the boat is listing too much. That is, if there isn't anything in the way, if you steer more upwind :p
      - lmilcin 7y ago
        This will actually depend on your course with regards to wind. There will be a course that will generate maximum heeling moment.
      - odonnellryan 7y ago
        Generally you'll heel over the closer you are into wind while your sails aren't luffing. Taking off the wind will make the boat heel less.
  - cjbprime 7y ago
    Yeah, and I think MCAS ended up fully deflecting the stabilizer on Ethiopian. Even with a somewhat more reasonable altitude, I wonder how long it takes to physically manually retrim from one end of the jackscrew to level flight. I think even the electric motor takes at least six seconds to do that.
    - _ph_ 7y ago
      From what I read the situation was made worse by the fact that they where flying a bit on the fast side even when they were not going down yet, increasing the load on the stabilizer.
- cjbprime 7y ago
  A normal person wouldn't, but you're probably overstating the reluctance an actual pilot would have. Being reluctant to push the nose down when in a bad situation would cause pilots of any aircraft to fail their first hour of stall training. It's more worrying that, since the procedure was removed from manuals and training, the pilots might simply not have realized that it would help.

deleted 7y ago

[deleted]

JshWright 7y ago

At least some simulators are capable of modelling those forces (I don't have any knowledge of the domain, but I would assume it's standard in "professional" simulators): https://www.youtube.com/watch?v=aoNOVlxJmow https://www.youtube.com/watch?v=aoNOVlxJmow

inferiorhuman 7y ago

In particular, the Ethiopian flight was in extreme overspeed (if I recall, past the max safe structural speed for the plane!) While the Ethiopian crew did have the overspeed warning going off, it was well below the "do not exceed" and "max dive" speeds. I'm not sure whether that was being modeled by the simulator, or if the simulation's model of trim wheel force is a correct one. It wasn't. Boeing's already admitted that their simulators don't correctly emulate the forces on the trim wheel.

salawat 7y ago
The borked AoA vane also meant the computer was not calculating airspeed correctly. They were in an Airspeed Unreliable situation, which warrants being generous with power based on the stage of flight. Climb-out from Adis Ababa (a hot and high airport) means you've got precious little excess in terms of sacrificial power to begin with. The MAX 8 could only take-off at all due to an unusually long runway as I recall.

jacquesm 7y ago

> It's quite plausibly physically impossible if the pilot happens to be less strong than this one, or if the aircraft's situation is worse than this simulator's. That simulation would have ended in a crash if they didn't abort it. So the pilots strength did not seem to matter and the situation was about as bad as it gets.