I'm assuming a system where the force from the engine thrust is balanced by the force transmitted through the wheels due to the acceleration of the treadmill (and the inertia of the wheels).
I'm not sure what calculation to do here, because the most applicable calculation is the one that you did yourself in the other current thread. Just take a look at that calculation and ask yourself what would happen if the treadmill accelerated more than the acceleration required to keep the plane stationary.
