henra, you touched on a serious point here. The plane had a lot of kinetic energy, mV^2. It also had 35,000' of potential energy. It had a specific velocity vector to that energy. Changing the velocity vector as projected on the ground requires trading mgh for mV^2, external force input, or both sufficiently gentle that the plane does not crumple and sufficiently large that the plane nearly stops in the air. God did not simply swat the airborne example of human hubris from the air. Something else did. We probably need to know how before we can determine what.
So what transitions and energy transformations can take place that would effect these scenarios? How might these energy transitions take place? And for each such transformation "why" might it take place?
We have a set of working presumptions based on the conditions of pieces found. The plane hit the water with "substantial" (how substantial?) vertical velocity and modest forward velocity with a vector roughly along the projection of the axis of the plane's body on the water.
One recurrent question never really answered for that theme is "how do you reconcile the observed fracture patterns with the VS breaking off in flight?" The sideways or even torque type stresses that the VS sees in flight would produce a quite different fracture pattern than the one observed. This is one example of what I mean by "how might these energy transitions take place?"
GreatBear's scenario needs the transitions explained. The data record gives him three tools to work with. Two are related to the communications outage. Was it loss of line of sight from antenna to satellite (body of the plane in the way) or loss of power later made up by restarting engines or the emergency system kicking in. The third tool is his imagination and experience.
In his scenario we have a really big and modestly breakable object containing hundreds of really breakable objects broken in a specific pattern that must come to a near stop along its former track almost instantly and converting it to a much lower velocity off to 90 degrees from its flight path.
mm43 had the same problem. He posted his banked turns graphs which essentially posit controlled turns rather than jet fighter aerobatics. It's a start. It does show a way to account for the forward velocity bleeding off in a slightly more gradual way with the plane ending up off to one side of its former track by around 90 degrees.
Presume first that the plane is not decelerated at more than about 3g. Much more than that would potentially cause things to break making everything in the analysis more difficult. Start simple work in complications later only if needed.
This may be a little over the top, mind you. The damage to the recovered corpses, perhaps people not strapped in, suggests they were not subjected to being thrown around the cabin so much as thrown to the floor of the cabin while in sitting positions. (At least that is my understanding.) Violent maneuvers that satisfy this condition seem questionable. Perhaps 1/2g to 1g is a better limit.
This isn't decrying GreatBear's analysis. It's simply requesting that energy and the energy state transitions be considered, too.