Originally Posted by metabolix
And the bonkersly long unrestricted airfields which also have a drop in Vr (albeit only a couple of kts at these places) I guess I'm going to have to put down to the fine tuning of calculations
And a quick question for non 737 drivers - does this phenomenon happen with your aircraft Improved Climb performance tables as well?
I wonder whether the length of the actual strip of tarmac is really the focal point of the issue. The relative improved performance gains are not primarily for lifting extra weight off the runway as such, but translate into maintaining obstacle clearance ability at higher weights than a normal take-off would allow. Achieving engine-out screen-height and avoiding fixed obstacles within the take-off 'cone' might not necessarily be coincident - ie it might be the obstacles that produce the limitation, even though the length of the runway is miles and miles and miles!