Spatial disorientation is the major causal factor in numerous aircraft accidents.
It occurs when pilots cannot perceive, understand or anticipate the state of their aircraft or the environment around them.
Spatial disorientation refers to the inability to determine position or relative motion occurring during periods of challenging visibility since vision is the dominant sense of orientation.
The body’s vestibular and proprioceptive systems collectively work to co-ordinate movement with balance, but can also create illusory non-visual sensations in the absence of strong visual cues, resulting in spatial disorientation.
Human senses are not naturally geared for the in-flight environment.
During flight, pilots may experience disorientation and loss of perspective, creating sensory illusions that range from false horizons to sensory conflict with cockpit instrument readings.
Illusions in aviation are caused when the brain cannot reconcile inputs from the vestibular and visual systems.
The visual system is the physiological basis of visual perception – the ability to detect and process light.
The system detects, transduces and interprets information concerning light within the visible range to construct images and build mental models of the surrounding environment.
The visual system is associated with the eye and functionally divided into the optical system including the cornea and lens and the neural system including the retina and visual cortex.
The vestibular system in humans is a sensory system that creates the sense of balance and spatial orientation for the purpose of co-ordinating movement with balance.
Together with the cochlea, a part of the auditory system, it constitutes the labyrinth of the inner ear.
[caption id="attachment_1143825" align="alignnone" width="714"] A diagram showing the semicircular canals of the ear which control the sense motions of roll, pitch and yaw.Diagram courtesy the FAA -[/caption]
As movements consist of rotations and translations, the vestibular system comprises two components: the three semicircular canals which are interconnected tubes located in the innermost part of the inner ear. They are stimulated by angular accelerations in the pitch, yaw and roll axis and the otoliths, which indicate linear accelerations.
The vestibular system sends signals primarily to the neural structures that control eye movement.
They provide the anatomical basis of the vestibulo-ocular reflex that is required for clear vision.
Signals are also sent to the muscles that keep humans upright and in general control posture.
These provide the anatomical means required to enable pilots to maintain their desired positions during flight.
Illusions involving the semicircular and somatogyral canals of the vestibular system of the ear occur primarily under conditions of unreliable or unavailable external visual references and result in false sensations of rotation. These include the leans, the graveyard spin and spiral, and the Coriolis illusion.
The "leans" is the most c
