RR_NDB;
I try very hard to leave hindsight bias behind and go where the available evidence and my experience and knowledge of the airplane take my thoughts. It doesn't always work, so disagreement, based upon further information and not just opinion, is always part of the process.
Believe me it is not pleasant to contemplate what has happened to this crew but as so many have said, it is crucial to find out what happened and why so that prevention takes place. In fact many things have already changed in the past year as a result of the available data in the form of recurrent training and so on.
It is a fact that airplanes, their systems and engines rarely fail mechanically, that navigation is extremely accurate, that autoflight is very good, that CFIT's and mid-air collisions are rare thanks to GPWS/EGPWS and TCAS, that satellites have made communications over vast areas of ocean almost routine, (though not here even though such wasn't likely an important factor), and that SOPs, CRM and things like checklist design have all contributed to the remarkable safety record of the industry.
It is therefore a fact that a very high percentage of accidents are HF accidents.
This is a primary reason for safety programs such as FOQA/FDM, which also have a crew-contact element (by a pilot's peers, not by management!), which is designed to address human factors issues and prevent untoward events.
So it is extremely important to understand what happened here and why, especially in Phase 2, and with two first officers and the ill-defined command and experience gradients which, I am sensing, may possibly also had had a cultural aspect.
These are SMS, HF and organizational areas of accident investigation and prevention. So, with reference to your comment, "Your thinking (on why's) i understand is concentrated in the crew (unexpected behavior) and considers the machine 'performed as expected'. ", I was not so much focused on the crew so much as it is where the available data is drawing attention. That means that new information, when or if it arises, always has the capacity to draw attention. This does not mean that design, and the machine is not the focus but that one places such attention in the context of the man-machine interface.
Designers cannot reasonably be expected to anticipate everything that will occur in an aircraft either by mechanical incident or crew action so it must be designed to fail gracefully as some have pointed out here, and this airplane failed gracefully - a loss of speed information does not necessarily result in a loss of control or loss of the aircraft. I don't think it is at all reasonable to expect that a designer will, in the course of such anticipatory processes, design against all outcomes that may or may not obtain in a fully-developed high altitude stall by line crews.
That said, even with a full NU THS, there was sufficient elevator authority and upwards force on the horizontal stabilizer and aft fuselage to lower the nose and un-stall the airplane albeit likely over as much as a 20,000ft loss of altitude. I think that is a remarkable bit of engineering. A level D simulator may not have the exact algorithms for post-stall behaviour but nor is it entirely without data and fidelity in such conditions.
Crew confusion must be examined very closely in both Phase 2 and 3. Post-pitch-up the PM was confused by the initial two very short stall warnings for example. Who knows how that may have influenced subsequent perceptions and input? The other aspect which I expect will be examined in the final report is the behaviour of the stall warning system below 60kts but this has been widely discussed.
It remains a concern as a former transport pilot that potentially irreversible actions were swiftly, unilaterally taken without adhering to SOPs, CRM communications standards and the handling of abnormals. Cockpit discipline and TEM (Threat/Error Management) processes are drilled into crews in each simulator session and are causes for failure of the ride if not executed to high standards. These processes intervene to prevent rushed actions while providing a basis for calm, measured and coordinated responses by both crew members. This isn't some elusive ideal, this is the normal standard by which transport aircraft are flown, so any unexpected divergence from this standard requires explanations and a willingness to closely examine crew actions where the data supports that kind of an approach. That is why I seem focused on the crew.