Vertigo: A Primer
Spatial disorientation is classified into three types.
-- Unrecognized spatial disorientation (Type I) refers to situations in which the pilot fails to perceive a change from the desired orientation.
-- Recognized spatial disorientation (Type II) occurs when the pilot realizes there is a conflict between the flight instrument readings and what his body senses is the spatial orientation.
-- Incapacitating spatial disorientation (Type III) refers to situations in which the physical symptoms accompanying disorientation — visual impairment, muscle spasms, nausea, or panic — are severe enough to incapacitate the pilot.
Among the illusions pilots may experience:
The Leans A somatogyral illusion in which, after a prolonged, gentle turn followed by a sudden return to level flight, a pilot will sense a turn (bank) in the opposite direction. A pilot experiencing the leans may lean in the direction of the original turn in an attempt to regain the perception of the correct vertical posture.
The Coriolis Illusion A somatogyral illusion in which, while the aircraft is turning, a pilot tilts his head — say, to read a map. When the head is tilted out of the plane of rotation, the pilot will experience a sensation of rolling. Depending on the nature of the turn, the pilot may also experience a sensation that the aircraft is pitching, yawing, or both.
The Graveyard Spiral Unaware the airplane is banked but sensing the nose drop and a loss in altitude, a pilot may pull back on the yoke to try to regain altitude or slow the rate of descent. The increase in back pressure on the control yoke usually results in a tighter turn and a drop of the nose, causing a further loss of altitude. The sequence may continue until the airplane stalls, breaks apart, or hits the ground.
The Inversion Illusion A somatogravic illusion in which, after a sustained climb in a high-performance aircraft, the pilot levels the aircraft, creating a lighter “seat bottom” sensation while the acceleration maintains the seat-back pressure. The sensation is that of the aircraft continuing to increase in pitch. Soon the pilot perceives the aircraft is inverted.