Aeromedical Factors

Vestibular Illusions direction causing the disoriented pilot to return the aircraft The Leans to its original turn. Because an aircraft tends to lose altitude in turns unless the pilot compensates for the loss in lift, A condition called the leans, is the most common illusion the pilot may notice a loss of altitude. The absence of any during flight and is caused by a sudden return to level flight sensation of turning creates the illusion of being in a level following a gradual and prolonged turn that went unnoticed by descent. The pilot may pull back on the controls in an attempt the pilot. The reason a pilot can be unaware of such a gradual to climb or stop the descent. This action tightens the spiral turn is that human exposure to a rotational acceleration of 2 and increases the loss of altitude; this illusion is referred to degrees per second or lower is below the detection threshold as a “graveyard spiral.” [Figure 17-5] This may lead to a of the semicircular canals. [Figure 17-4] Leveling the wings loss of aircraft control. after such a turn may cause an illusion that the aircraft is banking in the opposite direction. In response to such an Somatogravic Illusion illusion, a pilot may lean in the direction of the original turn in a corrective attempt to regain the perception of a correct A rapid acceleration, such as experienced during takeoff, vertical posture. stimulates the otolith organs in the same way as tilting the head backwards. This action may create what is known as Coriolis Illusion the “somatogravic illusion” of being in a nose-up attitude, especially in conditions with poor visual references. The The “coriolis illusion” occurs when a pilot has been in a turn disoriented pilot may push the aircraft into a nose-low or long enough for the fluid in the ear canal to move at the same dive attitude. A rapid deceleration by quick reduction of the speed as the canal. A movement of the head in a different throttle(s) can have the opposite effect, with the disoriented plane, such as looking at something in a different part of the pilot pulling the aircraft into a nose-up or stall attitude. flight deck, may set the fluid moving, creating the illusion of turning or accelerating on an entirely different axis. This action causes the pilot to think the aircraft is performing a maneuver it is not. The disoriented pilot may maneuver the aircraft into a dangerous attitude in an attempt to correct the aircraft’s perceived attitude. Graveyard spin For this reason, it is important that pilots develop an instrument cross-check or scan that involves minimal head movement. Take care when retrieving charts and other objects in the flight deck—if something is dropped, retrieve it with minimal head movement and be alert for the coriolis illusion. Graveyard Spiral As in other illusions, a pilot in a prolonged coordinated, constant-rate turn may experience the illusion of not Graveyard spiral turning. During the recovery to level flight, the pilot will then experience the sensation of turning in the opposite Figure 17-5. Graveyard spiral. Endolymph Cupola Tube No turning Start of turn Constant rate turn Turn stopped No sensation. Sensation of turning No sensation after fluid Sensation of turning in as moving fluid deflects accelerates to same opposite direction as moving hairs. speed as tube wall. fluid deflects hairs in opposite direction. Figure 17-4. Human sensation of angular acceleration. 17-7