(Edit May 2012-- my thoughts on this matter have now changed significantly-- I'm still convinced that the earth "feels" a downward push from the wing of an aircraft in flight, equal in magnitude to the weight of the aircraft, which is also equal to the upward gravitational attraction that the aircraft exerts on the earth, but I no longer believe that this downward force need involve any specific amount of downward momentum of the air (downwash). For more, see posts 58, 61, and 72. End edit.)
Originally Posted by DPATE
It sounds like you are saying the aircraft pushes air down and that that air travels downward from the plane and eventually hits the Earth, thereby enforcing Newton's laws.
Is that the premise of your argument?
The plane's gravity pulls upwards on the earth with a force equal to mg.
Something must be stopping the earth from accelerating upwards toward the plane, because a steady and indefinite upward acceleration of the planet is very inconsistent with conservation of momentum.
The thing that stops the acceleration can only be a downward push equal to the plane's weight (mg), which is somehow or another transmitted to the surface of the earth near the plane. I'm proposing that the downwash is the mechanism that imparts the downward force, equal to the plane's weight (mg), upon the surface of the earth near the plane.
Please see especially the last three paragraphs (starting with "This discussion is starting to branch off into several branches: ") of my last post above.