woohoo, another one!!
The plane does not move regardless of where the propulsion comes from.
As long as the plane is in contact with the conveyor, the "velocity" of the plane (regardless of propulsion) is translated to the wheels. The conveyor belt assures that the plane does not gain any speed relative to the outside area.
As the problem is stated, valid arguments can be made for either case and it all depends upon how the "speed" of the plane is defined.
so there :toungue sticking out smiley icon guy that I don't have access to if it even exists.