Originally Posted by
fgrieu
So
according to the WSJ (paywalled, but
regurgitated by Reuters) the pilots of ET302 applied the
2018-23-51 EAD to some degree, flipped the trim switches off, could not correct the nose down condition (or is it move the trim wheel nose up), then flipped the trim switches back on (contrary to the EAD), to no avail.
I ask (because I don't know):
- How hard it is to manually trim nose up, depending on airspeed, current elevator position, AoA..? I have read about an
elevator blowback issue, but do not know the details.
- If standard simulator training prepares to that procedure, complete with simulation of how hard it is to turn the wheel. This is critical:
If pilots are not well trained to trim up by manual action on the wheel,
then mandating them to make it the only way to trim up was nonsense.
IMO the critical factor in both crashes (and the difference from the previous Lion Air flights), may have been that the pilots (unintentionally) allowed the speed to rise excessively before trying to intervene with the cutoff switches. Since the auto-throttles were still engaged (they are not disabled by AOA errors and unreliable airspeed), and the aircraft was in the climb phase, application of normal thrust would have led to excessive speed instead of increasing altitude. In either scenario this would also have led to an urgent requirement to retract flaps due to overspeed limitations, allowing MCAS to activate (if it had not already done so).
Nowhere in the Boeing/FAA emergency AD was the requirement to disable auto-throttles, particularly in the event of MCAS activation immediately after takeoff. This may have been because auto-throttles still provide protection in other flight regimes. IMO this inadvertently led both sets of crews down a 'box canyon', where they could not regain control nor pull-up, due to excessive loads on the horizontal stabiliser. As the WSJ article and recent simulator tests imply, all of the well-meaning advice may have been nonsense in the light of actual events.
Edit:
CurtainTwitcher gives a better explanation of the speed issues.
Edit: Peter Lemme made this point last week as well:
https://www.satcom.guru/2019/03/aoa-...oeing-fix.html