"Greg Copeland" wrote
Nitpicking aside, I suspect that everyone agrees that in order for the
plane to take off it must move
forward along the conveyor.

Which is exactly my point! If you have a motoroized conveyor which
always reduces the plane's forward movement to zero

It doesn't say that the plane has no forward movement - it says that the
conveyor moves backwards at the same speed at which the plane moves
forward - that does not prevent the plane from moving forward.