Originally Posted by
coaldemon
Nothing required for Manual Trim from what I have heard. System has been tested and works. Having used it in test flights it is not that hard to move and I understand the FAA and Boeing have retested it recently. Once outside the envelope it may be a different story but then you are outside the certified envelope for the aircraft.
The manual trim issue occurs when the aircraft is substantially out of trim, and electric trim is not available, but that is well within the envelope of the aircraft, as both JT and ET were for the most part of their foreshortened flights.
That is the problem...
It may be argued that this condition can only occur from a failure such as MCAS, however the A300 accidents, (RCTP, RJNN the old one) and the A320 splash (LFMP) along with USAir 320 events out of Reagan, A310 aerobatics at UUEE and LFPG, all of those were aircraft that ended up considerable out of trim without a failure of the trim system at all. For a similar case in say a B737NG, try getting the plane to Vref on an approach, going TOGA and failing the stab trim (simulating a failure or runaway resulting in cutout)... watch the fur fly. This is the easy fault, judicious use of bank will give a crew time to manage the problem. Nose down being that much out of trim is less likely before MCAS existed, but still will be challenging, and will take up some sky. The saving grace is just that the likelihood of the AND case is not as high as the ANU case, if and only if MCAS is removed from the equation.