Originally posted by Evan
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0- 2500m is enough landing distance for most normal landings with moderate braking. I mean if you remove 1000 of the 2500m due twice-longer-than-normal flare, a deceleration of just 0.2G which is less than 4 kts/sec (a moderate deceleration, Autobrakes 2 in the 737) would let you to go from 150kts to 0 in the remaining 1500m. Note that I am combining an abnormally high landing speed, an abnormally long touchdown, and a normal but very moderate braking. That combo is a pretty thick slice of cheese. And you still have several more:
1- Assuming that the plane flew at that landing speed from the threshold to the touchdown point, the whole threshold to touchdown to stopping point journey would take 52 seconds. The plane ahead will most likely not be 2500m down the runway, the same spot that it was 52 seconds ago when the landing plane crossed the threshold.
2- The pilots will not just sit there looking the other plane static on the runway estimating that it will be tight or worse if they leave Autobrakes 2, and leave Autobrakes 2 being along the ride for the crash.
3- Even if any evasive maneuver is needed a the last moment because the layers #0, 1, 2 and 3 all failed, it would be a low speed event, maybe with an airplane stuck in the mud at worst. Not your "best outcome" above.
And I want to think that there are provisions in place such as if you have an overweight landing, a flapless landing, or a very high density altitude conditions, where you need a greater landing speed and greater stopping distance (layer #0 at risk), these operations would not be performed.
So why I still don't like it? It still has the crystal ball thing. It is easy to watch the video and see hoe long down the runway the plane landing / departing ahead was on the runway when the landing plane crossed the threshold. But it is very difficult to predict where it will be when you are clearing the landing airplane for landing. Now, withholding the landing clearance until the conditions are met (rather than clearing a plane for landing when another one is cleared or about to be cleared to land or take off in front of them on the same runway) would eliminate the crystal ball thing, rendering an accident almost impossible.
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