Originally Posted by Old Smokey
It's a constant pitch value to be flown for the Airborne portion of the Takeoff from Vloff through to V2. It does cater for the worst case condition.
Certification testing is based upon flight at the nominated fixed pitch attitude from Vloff through to V2. This is not unique to Boeing, at one of the manufacturer's acquired by Boeing the figure was / is 9°, and applies at all weights and environmental conditions.
Think about it, in the 1st segment we are told to fly V2 (and the FD is programmed for this), in the 2nd segment we are told to fly V2 or V2 plus a particular additive if a higher speed has been achieved (and the FD is programmed for this), in the 3rd segment we are told to fly a constant altitude (and the FD is programmed for this), and so it goes. What are they going to tell you to fly between Vloff and V2? An attitude which will ensure correct acceleration between the two is what is provided, 8° for the case in point. It COULD be varied at the manufacturer's discretion to squeeze the last drop of performance from the aircrat, but at this point in time, it's constant.
Hope that helps, search around on the forums, there’s a few discussions covering your question in more detail