Located inside your inner-ear, the vestibular system gives us a large portion of our sense of motion. It works great walking on the ground and durning other normal, daily activities. Taken into the 3-D realm of aviation, however, and it can play dangerous tricks on a pilot. The result is spatial disorientation--literally, not knowing which way is up. In this class we will explore how the vestibular system works, what flight conditions can trick it, and what pilots and engineers have done to avoid "spatial-D" and its potentially disastrous effects.