1jz,
Boeing is correct in stating that the WAT limit gradients are instantaneous. No need to go looking for a Boeing document because it is clearly stated in the applicable regulations. FAR 25.121(a), (b) and (c) require instantaneous gradients. The sole purpose of those requirements is to define the Operating Limitation stated in 25.1533(a)(1), which is also the operating envelope of weight-altitude-temperature conditions that need to be considered for takeoff performance data. Takeoff distance information, for example, is only valid within that envelope.
The continuous takeoff flight path, on the other hand, is defined in FAR 25.111 and 25.115. The net takeoff flight path is provided in the AFM as Performance Information (ref. 25.1587(b)) to permit compliance with operating regulations that require obstacle clearance.
FAR 25.121(b) requires a "steady gradient of climb (of not less than) 2.4 percent for two-engine airplanes (...), at V2 with the critical engine inoperative, the remaining engine at the takeoff power or thrust available at the time the landing gear is fully retracted".
Consequently, at the maximum takeoff weight limited by the climb requirements of 25.121(a) through (c), the gradient of the takeoff flight path will be not less than 2.4 % at the time the landing gear is fully retracted. After that point the gradient will gradually reduce due to the normal reduction of thrust with increasing altitude.
Last edited by HazelNuts39; 9th Aug 2013 at 21:03.
Reason: additional text, grammar