Altitude limitDDI merely says that:
If a creature has a specified altitude limit, the creature crashes at the end of its turn if it is flying higher than that limit.
When a creature is at ground level, is it at altitude 0 or altitude 1? That is: does a fly speed (altitude limit 1) allow the creature to end its turn 5 ft. above ground? Or does it force the creature to be at ground level at the end of its turn?