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They were saying you cannot counteract MCAS's control inputs with the elevator alone. Pulling on the yoke is not how you counteract a runaway stabilizer on th

They were saying you cannot counteract MCAS's control inputs with the elevator alone. Pulling on the yoke is not how you counteract a runaway stabilizer on the 737. I've pasted the relevant part of the QRH in a few previous comments. Yes, the stabilizer ultimately has more pitch authority under some circumstances. That may be what happened here, but if I'm interpreting the graphs on the preliminary report correctly I wonder about mechanical failure of some sort. This gets a bit more complex with the 737 because moving the yoke WILL actually stop one of the stabilizer trim algorithms, but not MCAS.

Someone1234 8y ago
> Pulling on the yoke is not how you counteract a runaway stabilizer on the 737. I've pasted the relevant part of the QRH in a few previous comments. It is how pilots learn to counteract nose down day one of pilot training. In many aircraft hard elevation will overpower even a faulty horizontal stabilizer. If the QRH was a panacea we would have 348 fewer loses today. > That may be what happened here, but if I'm interpreting the graphs on the preliminary report correctly I wonder about mechanical failure of some sort. There was a mechanical failure, the AoA sensor. I'm skeptical there needs to be more going on than MCAS due to the "repeated correction" unauthorized change Boeing made. > “The FAA believed the airplane was designed to the 0.6 limit, and that’s what the foreign regulatory authorities thought, too,” said an FAA engineer. “It makes a difference in your assessment of the hazard involved.”
- inferiorhuman 8y ago
  In many aircraft hard elevation will overpower even a faulty horizontal stabilizer In the 737 you can get into situations where the elevator has insufficient authority to overcome a stabilizer. Excessive pitch up (leading to a potential stall) that you can't counter by pushing on the yoke is exactly what MCAS is designed to prevent. There was a mechanical failure, the AoA sensor. A fixed offset from reality is an interesting failure mode, especially in two separate sensors (Lion Air replaced the alpha vane before flight 610), and even more interesting as it's the same alpha vane used in the 737 NG. The left alpha vane was being interpreted as almost exactly twenty degrees higher than the right.
  - 6nf 8y ago
    The left alpha vane was being interpreted as almost exactly twenty degrees higher than the right. Is that because the plane was in a banking maneuver at the time maybe? I dont know anything about planes but I heard that when you're turning the two sensors will disagree by some amount
    - inferiorhuman 8y ago
      Is that because the plane was in a banking maneuver at the time maybe? I dont know anything about planes but I heard that when you're turning the two sensors will disagree by some amount The difference in angle of attack was consistent throughout the entire flight (well up until the crash where the values began to converge). The threshold for the optional 'angle-of-attack disagree' warning is, I think, ten degrees. It seems very unlikely that the plane had a twenty degree bank angle for two entire flights.
    - cjbprime 8y ago
      I think it's been disclosed that in Lion Air the sensors were twenty degrees apart even when sitting on the runway before the flight. It is shocking that nothing checked for disagreement or communicated it to the pilots.

Someone1234 8y ago

> Pulling on the yoke is not how you counteract a runaway stabilizer on the 737. I've pasted the relevant part of the QRH in a few previous comments. It is how pilots learn to counteract nose down day one of pilot training. In many aircraft hard elevation will overpower even a faulty horizontal stabilizer. If the QRH was a panacea we would have 348 fewer loses today. > That may be what happened here, but if I'm interpreting the graphs on the preliminary report correctly I wonder about mechanical failure of some sort. There was a mechanical failure, the AoA sensor. I'm skeptical there needs to be more going on than MCAS due to the "repeated correction" unauthorized change Boeing made. > “The FAA believed the airplane was designed to the 0.6 limit, and that’s what the foreign regulatory authorities thought, too,” said an FAA engineer. “It makes a difference in your assessment of the hazard involved.”

inferiorhuman 8y ago
In many aircraft hard elevation will overpower even a faulty horizontal stabilizer In the 737 you can get into situations where the elevator has insufficient authority to overcome a stabilizer. Excessive pitch up (leading to a potential stall) that you can't counter by pushing on the yoke is exactly what MCAS is designed to prevent. There was a mechanical failure, the AoA sensor. A fixed offset from reality is an interesting failure mode, especially in two separate sensors (Lion Air replaced the alpha vane before flight 610), and even more interesting as it's the same alpha vane used in the 737 NG. The left alpha vane was being interpreted as almost exactly twenty degrees higher than the right.
- 6nf 8y ago
  The left alpha vane was being interpreted as almost exactly twenty degrees higher than the right. Is that because the plane was in a banking maneuver at the time maybe? I dont know anything about planes but I heard that when you're turning the two sensors will disagree by some amount
  - inferiorhuman 8y ago
    Is that because the plane was in a banking maneuver at the time maybe? I dont know anything about planes but I heard that when you're turning the two sensors will disagree by some amount The difference in angle of attack was consistent throughout the entire flight (well up until the crash where the values began to converge). The threshold for the optional 'angle-of-attack disagree' warning is, I think, ten degrees. It seems very unlikely that the plane had a twenty degree bank angle for two entire flights.
  - cjbprime 8y ago
    I think it's been disclosed that in Lion Air the sensors were twenty degrees apart even when sitting on the runway before the flight. It is shocking that nothing checked for disagreement or communicated it to the pilots.