The Anal Equinox is a rare event that occurs when some helicopter pilots make ever tightening, successive, 360 degree turns. They actually cross the rectal event horizon and fly up their own alimentary canals.
 This phenomena was seen mainly among helicopter Scout pilots in Vietnam. Occasionally they could completely disappear for short periods of time. Cobra high bird crews can attest to this fact.
 WARNING!   Non-Scout type aviators must not attempt this maneuver without the supervision of an onboard, qualified instructor pilot.
 Some less skilled pilots attempting the maneuver only partially encountered the Equinox to their shoulders and suffered the dreaded Rectal/Cranial Inversion (RCI) and thus exacerbated the condition by depriving the brain of oxygen, usually resulting in catastrophic uncontrolled aircraft contact with the ground.
 The secrets of the Anal Equinox were never taught in flight school and are closely guarded by the Aero-Scout community. The uninitiated are unable to complete the process and are often doomed to repeat iterations of the RCI.
 

The Old Scout