Quotes from Concours77:
(1)
"... the elevators return to "neutral" and the THS has actually "supplanted" the elevators as primary flight control?"
No, the THS remains the secondary flight control, having merely backed-up the activity of the elevators, which remain always the primary. If at any time the PF gives consistent inputs in the reverse sense, the THS will in due course travel in the appropriate, opposite direction. The auto-trim has no bias in one direction or the other, and it is certainly not a ratchet-type device.
(2)
"I fall back on the first lesson of trim, "not for maneuvering". But for tuning the attitude to allow continuous flight without constant correction, or deflection?"
The first lesson of trim is ALWAYS to use the primary control first, and then unload the primary control with trim. Never use trim as the primary control, except (once in many lifetimes) when the primary control fails.
(3)
"To the extent that aft loading of fuel helps fuel economy, it also challenges the stability of the airframe?"
No. Life is a compromise in regard to safety and stability, or we would never get out of bed. And so is aircraft stability.
(4)
"Imagine, "briskly Push the controls Nose Down, hold a descent, and carefully ascend when the risk of secondary Stall, is mitigated?"
I maintain the flight crew were cheated of that opportunity...."
First of all, as far as we know the two co-pilots never recognised that the aircraft was stalled, which is what Machinbird's hypothesis is investigating.
AFAIK they never attempted a stall recovery.
Had they attempted a stall recovery, would they have been cheated of it? IIRC, Owain has previously calculated that, even with the THS at full nose-up (NU) trim, there is enough elevator authority to pitch the A330 down. And there is evidence that the A330, height permitting, is recoverable from extreme alphas as in AF447. But it's true that the rate of pitch-down would be lower with full NU than a lower angle.
Setting that aside, there comes a point in any control-departure when an aircraft cannot be recovered before impact. This crew took the aircraft to that point, and then well beyond it. They seem to have misdiagnosed an overspeed when it should have been evident that the (presumably unintended) rapid climb of no less than 2000 ft would have depleted the vast majority of the aircraft's kinetic energy.