Originally Posted by
Chris Scott
Hi James,
Yes: the gear definitely absorbs vertical kinetic energy, preferably without collapsing in the process! I'm afraid you are now taking this topic well beyond my expertise. I have suggested that the aeroplane would have remained intact, had it contacted the runway at the same VS; but the truth is, I don't know. The AAIB has not stated the VS.
If the landing gear collapses on a runway, my GUESS is that there is likely to be less secondary damage to the rest of the aircraft than on grass. When the engine nacelles strike a runway, they will not dig in; likewise the nose or a wing tip.
Chris
I don't know the design details on the 777 specifically, but from what I do know of design of similar sized craft, the oleos will absorb vertical forces up to a point, but when it comes to horizontal (drag) forces - eg. when landing on grass - the gear is
supposed to detach. My understanding is that it also is
supposed to detach cleanly and without damaging the main spar and fuel tanks (for fairly obvious reasons).
In this case, it looks like the gear (at least on one side) punched up through the wing structure
prior to detaching due to the drag. From that observation, my fellings are that either:
a) the 777 gear didn't detach cleanly (as, I think, it will have been designed to do)
or
b) the vertical forces were way over the capability of the gear, at the point of impact, before drag forces could detach the gear - i.e. VS was beyond the limits of the gear.
If it's (b) then my guess is that the vertical forces will be the same on a runway (maybe more since soggy grass
might have absorbed some) and you would still punch the gear up through the wing. The gear may or may not detach after that, but the damage to the wing would have been done - my guess is that the wing (main spars) is the major damage that has written the hull off. Also, while the plane (with gear or not) might slide easier on the runway, wet grass would be a lot less likely to create sparks, which might be a consideration when you've got fuel everywhere...
Overall, I think it is quite possible that where they came down was the best place (from a survivability point of view) to do so
for that impact.
However, I'm not sure any of this is a useful comparison since I would be very suprised if, in the same circumstances, you managed to extend the flight as far as the runway and still have the same sink rate (but now I'm well beyond my expertise...).