I agree that any obstacles penetrating the 35ft obstacle clearance on a net takeoff path of 1,6% will lead to a higher required net takeoff path and thus gross takeoff path.
But this is a far 121.189 Operator requirement not a far25 certifying requirement like the 2,4% gradient.
In that sense the 1,6% figure is irrelevant, because as operators we need to take the actual obstacles into account and assure that the net path clears them by 35ft.( 121.189 d) We don't do this by starting of at 2,4%. It is done by taking all relevant obstacles into account, add 35 feet, determine the net path. Then add the penalty and thus determine the gross flightpath required. This could be 2%, 3% 5% etc...
For all these percentages you could make a specific WAT table that determines the limiting weight.
If there are no obstacles we are still limited by certifying limits (121.189a) like the 2,4% 2nd segment WAT limit (or required groos obstacle climb gradient is less than the certifying limit)
Last edited by 737Jock; 26th February 2012 at 22:48.