 Complete the following phrase:  The graveyard spiral and graveyard spin are both caused by the acclimation of the semicircular canals to prolonged rotation; after a banked turn in the case of the graveyard spiral or spin for the graveyard spin of approximately 20 seconds, the fluid in the semicircular canals has been entrained into motion by friction, and the vestibular system no longer perceives a rotational acceleration. If the aviator then ends the turn or spin and returns to level flight, the continued motion of the fluid will cause a sensation the aircraft is turning or spinning in the opposite direction, and the pilot may re-enter the original turn or spin inadvertently; the aviator may not recognize the illusion before the aircraft loses too much altitude, resulting in a collision with terrain or the g-forces on the aircraft may exceed the structural strength of the airframe, resulting in catastrophic failure. One of the most famous mishaps in aviation history involving the graveyard spiral is 