Spatial disorientation refers to a person’s mistaken perception of orientation, direction, and balance relative to his environment, usually due to the lack of a fixed frame of reference. In the context of aviation, it refers to a pilot’s mistaken perception of an airplane’s orientation, direction, and balance relative to the earth, essentially because the movement inherent in aviation is unnatural and unfamiliar to the human body.It is the primary reason for airplane accidents.
Statistics show that between 5 to 10% of all general aviation accidents can be attributed to spatial disorientation, 90% of which are fatal (“Spatial Disorientation”). It is therefore important to understand the causes of this problem and to find effective solutions for it.TypesThere are three types of Spatial Disorientation in aviation: Unrecognized (type 1), Recognized (type 2), and Incapacitating (type 3) (Erickson, 2004).Unrecognized disorientation, the most dangerous type, is when the pilot does not perceive that anything is wrong, and is totally unaware of any orientation problem, real or otherwise. In such a situation the pilot believes that everything is going normally (“Disorientation”).The second, and also most common, type, is recognized disorientation. It is experienced by almost all pilots. It is when the pilot perceives some inconsistency between his sense of orientation and the airplane instruments.
However, the pilot does not necessarily perceive it as spatial disorientation; he may incorrectly assume that the instruments are malfunctioning, and may not do anything because of very strong vestibular indications of correct orientation.. But most often the pilot will be able to rectify the situation in favor of the aircraft’s instruments. (“Disorientation”)The third type, incapacitating disorientation, although also recognized by the pilot, differs from the second type in that the pilot is unable to perform any attempts to resolve any perceived inconsistency in orientation. Some causes are strong vestibular-ocular disorganization, strong vestibular spinal reflexes to the shoulder and arm, or even such intense fear or panic that he is unable to make a rational decision to recover the aircraft. (Gomez)Mechanisms of OrientationIn aviation, roughly 90% of sensory cues that help establish orientation are visual, making vision the most important determinant of orientation.
Clear weather and a clear view of the horizon will provide a pilot with ample visual cues—that is, a fixed reference—so that the possibility of serious sensory disorientation is negligible; but these same visual cues can cause spatial disorientation in the absence of a clear view of the earth’s surface and horizon. Of course disorientation can be overcome by referring instead to the aircraft’s instruments for orientation information. (Gomez)Also important is the vestibular system. The vestibular system, a complex of partially fluid-filled canals in the inner ear, is responsible for sensing and controlling motion. However, the fluid in the ear reacts only to non-uniform movement—sustained motion is not detected (“Sensory Illusions in Aviation,” 2006).
As a result, a prolonged and uniform motion, such as a spin, is eventually sensed vestibularly as “normal”, and a sudden return to an actual regular and level orientation is perceived vestibularly as a deviation from the normal orientation, wherein the pilot will experience disorientation, and will try to compensate by returning the aircraft to the previous mode of movement. (Gomez)A pilot can actively and effectively suppress disorienting vestibular sensations when there is an ample amount of visual cues. This ability is developed in training and in flight through repeated exposure to disorientation-inducing situations.
This ability is, however, severely restricted in the absence of visual cues. in the absence of visual cues, vestibular sensations may win over and cause disorientation. (Gomez)Examples“The Leans”. This is the most common aviation illusion, caused by a sudden return to a level orientation after a prolonged turn unnoticed by the pilot (a rotational acceleration of 2 degrees per second or below is undetectable by the vestibular system). The pilot may incorrectly perceive that the level flight is not level, and the pilot will lean in the direction of the original turn to regain a “correct” vertical posture. (“Sensory Illusions in Aviation,” 2006)The Graveyard Spiral. This occurs after a prolonged bank turn. A pilot coming from a prolonged bank turn will incorrectly perceive (vestibularly) that the orientation during the turn is level, and upon return to actual level flight, the pilot will become disorientated and incorrectly perceive that the actual level flight is banked in the opposite direction of the original turn.
If the pilot believes the illusion and returns to the banked turn, the plane will continue to lose altitude and crash. (“Sensory Illusions in Aviation,” 2006)The false horizon illusion is when the pilot mistakes a cloud formation with the horizon or ground. A sloping cloud bank below the aircraft may be perceived as horizontal, thus the pilot will fly the plane banked, believing it to be level. (“Disorientation”)The height-depth perception illusion occurs because of a lack of visual cues that aid in depth perception. This can happen when flying over desert, snow, or water. Because of the misperception the pilot may fly dangerously low. (“Disorientation”)RemediesPilots need to keep in mind that spatial disorientation cannot be eliminated (at least in the near future), and that misleading sensory cues can be predicted and prepared for (“Disorientation”).
External and instrument cues should not be mixed, especially when visual and vestibular cues are suspect. (Gomez)Hasty, intuitive actions can be made when experiencing disorientation; hence these actions should be delayed in favor of checking visual references and instruments (“Disorientation”).A pilot should never fly without visual reference points, either from the actual horizon or that from the instruments. And, since the probability of instrument malfunction is low compared to the probability of spatial disorientation, instrument readings should be trusted foremost when in doubt about sensory cues (“Disorientation”). The possibility of spatial disorientation can be minimized by frequent and systematic monitoring of critical flight parameters as displayed by instruments (Gomez).Ground based physiological training and in-flight training should be taken (Gomez). Training, instrument proficiency, well-being, and good aircraft design can reduce spatial disorientation (“Disorientation”).
ReferencesSpatial Disorientation. Pilotfriend. Retrieved April 28, 2006, from http://www.
pilotfriend.com/aeromed/medical/spat_disorientation.htmErickson, R. Spatial Disorientation (SD) Happens Only to the Other Guy. (2004, June). Naval Safety Center. Retrieved Aril 28, 2006, from http://www.
htmDisorientation. South African Civil Aviation Authority Online. Retrieved April 28, 2006, from http://www.caa.co.za/resource%20center/av.
%20medicine/docs/Disorientation.htmGomez, G. Spatial Disorientation : Something Old ; Something New. Indian Society of Aerospace Medicine. Retrieved April 28, 2006, from http://www.
isam-india.org/essays/cme_spatial.shtmlSensory Illusions in Aviation. (2006, April 23).
Wikipedia. Wikimedia Foundation. Retrieved April 28, 2006, from http://en.wikipedia.org/wiki/Sensory_Illusions_in_Aviation#Sensory_illusions