Human beings have obviously evolved to operate in a terrestrial playing field. But our big brains and ingenuity have allowed our advancements in technology to far outpace our ability to adapt. So, what happens when you take a terrestrial bi-pedal animal like a human and put them in a quickly accelerating aircraft that adds an additional dimension to any possible motion? Well, you run the risk for sudden, and in some cases incapacitating, disorientation. This is Spatial Disorientation.
Spatial disorientation (commonly referred to as Spatial-D) is the inability to determine one's position, location, and motion relative to their environment. Along with Hypoxia and G-induced loss of consciousness (G-LOC), Spatial-D is one of the most common causes of fatality from human factors in aviation. Spatial-D regularly affects pilots in all aircraft, whereas only military or acrobatic pilots in high performance aircraft have to worry about suffering a G-LOC. Another difference is that G-LOC can be prevented through the Anti-G Straining Maneuver, but there is no anti-Spatial D maneuver. The mishap leading to the death of John F. Kennedy Jr was likely a result of unrecognized Spatial-D.
PHYSIOLOGY - SPATIAL ORIENTATION
It is evident the human body did not develop for the purpose of flight in 3-dimensional space. In order to fully understand this phenomenon, it is vital to appreciate the anatomy and physiology that we constantly use to orient ourselves.
One's capacity to know their body's location and orientation in any setting is based on four functioning bodily systems. Sensory information for orientation is provided by our:
- Visual System
- Vestibular System
- Proprioceptive System
- Auditory System
VISION
Out of all of the systems listed above, vision is by far the most vital sense for determining orientation. Without vision, determining one's position on the ground proves difficult. The task of flying in the air without vision would be nearly impossible.
Visual perception is often separated into two separate functionalities- focal vision & ambient vision. Focal vision is used for object recognition and occurs whenever light reflected from an object is focused on the fovea in the back of the retina. This process is dominated by photoreceptors known as cone cells. This type of vision uses only the central 30 degrees within the visual field. Ambient vision, on the other hand, is described as answering the "Where?" question and is derived from stimulation of photoreceptors known as rods in the periphery of the retina.
VESTIBULAR SYSTEM
UNDERSTANDING THE PHYSIOLOGY OF THE VESTIBULAR APPARATUS
Although not as vital as the visual sensory system, the role of the vestibular apparatus located in the inner ear is also incredibly vital to spatial orientation. This system works synergistically with the visual system to assist with stabilization of an image on the retina when the head and/or body is in motion, and also acts independently to provide sensory information of the body's position and motion in the absence of vision.
CATEGORIES OF SPATIAL-D
There are variety of specific types of Spatial D. But Spatial-D is broadly divided into three categories:
- Unrecognized - Type 1
- Recognized - Type 2
- Incapacitating - Type 3
It is thought that more than half of the mishaps caused by Spatial-D are a consequence of Type 1 SD and that a majority of the remainder are Type 2. Type 3 SD may be due to various causes, such as a nystagmus (rhythmic beating of the eye) preventing the pilot from physically being able to see flight controls, dominant reflexes that hijack the controls, a cognitive inability to solve the disorientation, or incapacitating fear. These examples of Type 3 Spatial-D are fortunately quite rare.
NAVY PILOT BARANY CHAIR TRAINING
Recent upgrades with Ground Collision Avoidance Technology (GCAT) such as the DoD's Auto-GCAS is expected to save pilots experiencing unrecoverable Spatial D.