With all due respect, it still doesn't matter. Under the assumptions presented with this question, the treadmill matches the plane's speed...no matter the change in acceleration, the speed would still be matched. What loss can be accounted for by the wheel bearings/suspension/friction/etc. is inconsequential because the situation is essentially one where friction can never be overcome to produce forward motion. So the engine can provide a constant, increasing, decreasing, or non-existant acceleration, but the speed would continue to be matched.
well, he IS an engineer.
Me and Scott, who were both arguing the opposite, are also engineers.
I personally found physics I to be one of the more fun classes in our curricula.