The maximum TOW limited by climb requirements (WAT limit) for Transport Category Airplanes is based on the most limiting of three T.O. climb requirements with one engine inoperative (gradients for twins):
25.121(a): 0%; Vlof; gear down; T.O. flap, T.O. thrust
25.121(b): 2.4%, V2; gear up; T.O. flap; T.O. thrust
25.121(c): 1.2%; Vfto; gear up; flaps up; M.Cont. thrust
The conditions for these requirements differ in some details from those used to establish the take-off flight path, notably with respect to the variation of thrust with altitude.
Originally Posted by Jock737
The climb limit therefore only arises when the gross flight path minus 0,8% (net flight path) does not clear all obstacles by at least 35ft.
That is not correct. The WAT limits are a certificate limitation and apply regardless of obstacle clearance considerations for all types of operations. Obstacle clearance by the Net TOFP is required by operating regulations such as FAR 121 for Air Carriers.