Thank you for your explanation guys.
I accept the balanced field one, and I also understand that the range of V1 you can get in some situations, allow you to accept an intersection T.off.
But I understand better Mutt's word. it seems obvious to me that if you change one factor (weight or distance available) you screw up your nice calculations.
I guess am also gonna ask to alex whittingam what is his point about that.
Thank you all
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Flying is not dangerous, crashing is