ACtually you still miss the point....
of course the velocity matters.....but the velocity only matters because it changes....
if the plane hits the building and continues to travel at the same velocity....no force on the building...
but what happens is that the plane loses velocity(i.e. decelerates)...thus causing force on the building.....
But i guess you already knew that.....
We really need to explain to you again.....when velocity changes....it becomes acceleration
So when momentum changes...it is force...not momentum any longer
Good luck with that job...Im sure if you mention any of this to a nuclear/chemical/electrical Engineer...they will laugh till they are blue in the face.....

The force is proportinal to the momentum, derived from the mass and veloctiy of the plane at the moment of impact. The F = 0 only when P = 0. (i.e. m or v =0)
Post a mathmatical expression to the contrary.