Originally Posted by reventor
1) Did the pilots deliberately put the plane down on the grass?
If with "deliberately" you mean that they had a choice of touchdown somewhere else and still took the first patch of green after the perimeter fence:
Not known, like answers to all of these questions, but
probably not.
Originally Posted by reventor
2) Would the outcome, in retrospect, likely have been as fortunate had they landed (with same force) on the runway?
Probably not, but landing with the same sink rate on the runway would not have been a reasonable option.
We don't know what the vertical velocity was at the time of impact with the grass, but probably it was in the region of survivable even as an impact with a harder surface (much below 2000 fpm). Disruption of the fuselage and fire has been a common result in impacts worse than which can just barely destroy the undercarriage.
Originally Posted by reventor
3) Was the stall-like nose up movement at the very end as seen in the video intentional or an unwanted consequence of whatever failures the aircraft suffered?
Probably intentional. The official AAIB initial information has revealed only failures with the engine response to throttle input, but does not yet rule out other problems. By Occam's they are extremely unlikely though, because the already very unlikely throttle problem fully explains the whole event.
Originally Posted by reventor
4) If intentional, what was the purpose of it, assuming the angle of attack was higher than it should have been for a smooth landing, as appeared to be the case to my untrained eyes?
The logical purpose was to reach the RESA or in other words the airport proper and avoid crashing in inhospitable terrain before it.
The crew probably traded momentum (speed) for lift to clear the boundary obstacles. It's a dangerous manouvre, but clearly justified by the results. Generally you would not want to slow down because this actually increases the sink rate, since you will be flying at a lower than optimal lift to drag ratio, resulting in an impact closer to the point of upset. But that scenario assumes you will be touching down at V
l/d, and not trading speed for more lift and more distance.
I think the main idea behind your questions is the assumption that the crew had a choice of landing on the runway, but I think the circumstances of the crash indicate that they didn't. If they had even a little bit of more thrust or speed while crossing the airport perimeter, they most likely would not have landed much further, but instead with less sink rate and less damage, still ending quite near where they did. It would not have made any sense to try to reach the asphalt with a presumably dangerously low energy state, but instead to try to arrest the excess sink rate which resulted in quite heavy structural damage and some injuries to the passengers and crew.
Originally Posted by reventor
5) It is generally not entirely unreasonable to assume that the timing of the failure was crucial? A little shift in time and they either fall down in the residential area or make a reasonably normal landing.
I think it's a
good assumption. It has been speculated that the approach may not have been properly stabilised, having support mainly from eyewitness accounts, which would explain the throttle demand at that specific point of failure. However, it was a relatively gusty day and some (larger than average) throttle adjustment was necessary for even a perfect approach.