737Jock,
Can you point me too a reference that says it only momentary?
I think you chose to emphasise the wrong part of the regulation.
far 25.121 b) Takeoff; landing gear retracted. In the takeoff configuration existing at the point of the flight path at which the landing gear is fully retracted, and in the configuration used in §25.111 but without ground effect, the steady gradient of climb may not be less than 2.4 percent for two-engine airplanes, 2.7 percent for three-engine airplanes, and 3.0 percent for four-engine airplanes, at V2 and with --
The point at which the performance must be demonstrated is emphasised, the nature of the performance must be steady and not as a result of any temporary trickery like zooming/speed bleed, ground effect, etc., but there is nothing that says it must have the same value at the end of the path as it did at the beginning.
Stay Alive,