4 ms·

The pilot can run the trim in the other direction using the normal switches on the yoke. You can see that if you look at the trim position graph in the Lion Air

The pilot can run the trim in the other direction using the normal switches on the yoke. You can see that if you look at the trim position graph in the Lion Air accident. For some reason before the crash the pattern of repeatedly correcting changes, possibly because he handed control to the first officer.

Rooster61 8y ago
"The undated EASA certification document, available online, was issued in February 2016, an agency spokesman said. It specifically noted that at speeds greater than 230 knots (265mph, 425kph) with flaps retracted, pilots might have to use the wheel in the cockpit’s center console rather than an electric thumb switch on the control yoke. " So, yes and no. It gives SOME control over the trim, but if the trim keeps getting bumpped progressively higher by the MCAS, it will eventually outstrip the yoke control. My guess is that that change you mentioned is the threshold at which their yoke trim control became insufficient.
- VBprogrammer 8y ago
  This appears to be a reference to https://www.easa.europa.eu/sites/default/files/dfu/IM.A.120%20Boeing737%20TCDS%20APPENDIX%20ISS%2010.pdf https://www.easa.europa.eu/sites/default/files/dfu/IM.A.120%... issue 10. They are saying there that near Vmo (maximum operating speed) with an aft centre of gravity (the aircraft loaded in a specific way) there might not be enough nose down trim authority available within the limits of the electric trim to completely trim the aircraft (allow the pilot to relax the forward pressure on the yoke). In the crashes there was too much nose down trim and MCAS kept adding it more. They are trying to move it in the other direction. Pants reporting but nothing to see here.
  - Rooster61 8y ago
    Just to clarify, it's B-05/MAX under Issue 10. Took me a minute to find it. > there might not be enough nose down trim After reading it, I'm not sure how you are gathering that it's only nose down trim. It only mentions an inability to completely set the trim longitudinally. Longitudinal doesn't mean in one direction. It only indicates which plane we are talking about, which in this case is pitch. > Vmo (maximum operating speed) with an aft centre of gravity (the aircraft loaded in a specific way) "The aisle stand trim switches can be used to trim the airplane throughout the flight envelope and fully complies with the reference regulation Simulation has demonstrated that the thumb switch trim does not have enough authority to completely trim the aircraft longitudinally in certain corners of the flight envelope, e.g. gear up/flaps up, aft center of gravity, near Vmo/Mmo corner, and gear down/flaps up, at speeds above 230 kts" The issue mentions that there are certain corners, and lists what you posted after e.g. That isn't the only corner case in which the yoke trim control becomes insufficient.
    - VBprogrammer 8y ago
      I was reading between the lines on the fact that the scenarios the listed involved high speeds (which generally need nose down trim) and an aft centre of gravity which also needs nose down trim. Further, the section on EUSA's position clarifies that they wanted to improve the margin of safety on an out of trim dive, this is where 3 seconds of nose down trim (incidentally, that's how long they expect it to take for a mediocre pilot to identify a trim runaway) are applied without pilot intervention and the pilot has to demonstrate controllability. But that point is pretty moot because the electronic trim cannot drive the jackscrew to the extremes that the manual trim wheel can, but it can return from the extremes to the centre. MCAS is driving trim to the nose-down extreme and the pilot is trying to return it to neutral.
      - Rooster61 8y ago
        That makes sense. Thanks for the clarification.

Rooster61 8y ago

"The undated EASA certification document, available online, was issued in February 2016, an agency spokesman said. It specifically noted that at speeds greater than 230 knots (265mph, 425kph) with flaps retracted, pilots might have to use the wheel in the cockpit’s center console rather than an electric thumb switch on the control yoke. " So, yes and no. It gives SOME control over the trim, but if the trim keeps getting bumpped progressively higher by the MCAS, it will eventually outstrip the yoke control. My guess is that that change you mentioned is the threshold at which their yoke trim control became insufficient.

VBprogrammer 8y ago
This appears to be a reference to https://www.easa.europa.eu/sites/default/files/dfu/IM.A.120%20Boeing737%20TCDS%20APPENDIX%20ISS%2010.pdf https://www.easa.europa.eu/sites/default/files/dfu/IM.A.120%... issue 10. They are saying there that near Vmo (maximum operating speed) with an aft centre of gravity (the aircraft loaded in a specific way) there might not be enough nose down trim authority available within the limits of the electric trim to completely trim the aircraft (allow the pilot to relax the forward pressure on the yoke). In the crashes there was too much nose down trim and MCAS kept adding it more. They are trying to move it in the other direction. Pants reporting but nothing to see here.
- Rooster61 8y ago
  Just to clarify, it's B-05/MAX under Issue 10. Took me a minute to find it. > there might not be enough nose down trim After reading it, I'm not sure how you are gathering that it's only nose down trim. It only mentions an inability to completely set the trim longitudinally. Longitudinal doesn't mean in one direction. It only indicates which plane we are talking about, which in this case is pitch. > Vmo (maximum operating speed) with an aft centre of gravity (the aircraft loaded in a specific way) "The aisle stand trim switches can be used to trim the airplane throughout the flight envelope and fully complies with the reference regulation Simulation has demonstrated that the thumb switch trim does not have enough authority to completely trim the aircraft longitudinally in certain corners of the flight envelope, e.g. gear up/flaps up, aft center of gravity, near Vmo/Mmo corner, and gear down/flaps up, at speeds above 230 kts" The issue mentions that there are certain corners, and lists what you posted after e.g. That isn't the only corner case in which the yoke trim control becomes insufficient.
  - VBprogrammer 8y ago
    I was reading between the lines on the fact that the scenarios the listed involved high speeds (which generally need nose down trim) and an aft centre of gravity which also needs nose down trim. Further, the section on EUSA's position clarifies that they wanted to improve the margin of safety on an out of trim dive, this is where 3 seconds of nose down trim (incidentally, that's how long they expect it to take for a mediocre pilot to identify a trim runaway) are applied without pilot intervention and the pilot has to demonstrate controllability. But that point is pretty moot because the electronic trim cannot drive the jackscrew to the extremes that the manual trim wheel can, but it can return from the extremes to the centre. MCAS is driving trim to the nose-down extreme and the pilot is trying to return it to neutral.
    - Rooster61 8y ago
      That makes sense. Thanks for the clarification.