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. I have personally lost a good friend as a consequence of this phenomenon. On 28 January 2013, my former climbing partner and friend Maj Luc “GAZA” Gruenther, became disoriented and crashed his F-16C over the Adriatic Sea. This event reestablished for me the fact that ANY AVIATOR, AT ANYTIME can fall prey to this deadly human factor.
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
Let’s look at each of these independently below.
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. This is what you as the viewer is directly looking at. It is often said that focal vision answers the question of “What?” and relies on higher cognition for interpretation.
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 (corresponding to peripheral visual fields). You may recall that rods function better than cones in darker environments, but also detect far less detail and color recognition. This type of vision is usually processed subconsciously, and therefore can provide vital information to one’s position relative to their environment while the central focal vision focuses on the particular object of interest. Consider the instance when you are sitting in a parked car at rest facing forward and the car next to you begins to back out. Your peripheral vision senses this motion and your brain often interprets this data as if you are moving forward.
Although not as vital as the visual sensory system, the role of the vestibular apparatus located in the inner ear is also incred 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.
UNDERSTANDING THE PHYSIOLOGY OF THE VESTIBULAR APPARATUS
The anatomy of the vestibular apparatus resides within the bony labyrinth of the inner ear, located in the temporal bones of the skull. The cochlea, the vestibule, and the semicircular canals make up the bony labyrinth. The cochlea is the sensory organ for hearing. The vestibule is comprised of the otolith organs, the utricle and saccule, which sense linear acceleration. The semicircular canals, on the other hand, sense angular or rotational motion and accelerations of the head. Within the various vestibular end organs is a fluid called endolymph.
Although the actual way in which mechanical energy in the form of motion and acceleration translates into a neural input is quite complicated, it should suffice to say that relative motions and accelerations provoke either movement of the endolymph (fluid in the inner ear) and/or other moving parts within the vestibular apparatus. When these materials move, microscopic projections known as cilia from sensory receptors called hair cells physically bend. The direction that the cilia bends will translate into either a cellular depolarization or hyperpolarization, thus initiating or terminating an action potential that travels down neural pathways to the brain for further interpretation. In this way, mechanical energy from physical motion and position are converted into an biochemical electrical neural signal, which is then transformed by the brain into a spatial map of one’s orientation.
PROPRIOCEPTIVE & AUDITORY SYSTEMS
The third way in which humans sense their position and motion is through proprioceptors in connective tissue, joints, and the skin. Muscle spindles, Golgi tendon organs, cutaneous mechanoreceptors and other sensory receptors are the mainstay of this system. Each of these relay information about the relative position and interaction of the body’s extremities and skin with their environment. Lastly, the sense of hearing (acoustic energy transmitted to the cochlea from vibration of the eardrum through the three small bones known as the hammer, anvil and stirrup) has also demonstrated an ability to assist with spatial orientation thru perceiving the location of a sound’s source (kind of like a very primitive bat). When one is said to be “flying by the seat of their pants”, they are invoking sensory cues from these latter three systems rather than the dominant sense of vision. It’s often difficult for a pilot to even describe how they are perceiving their position when using these systems as this all happens fairly subconsciously.
PATHOLOGY – SPATIAL DISORIENTATION (SPATIAL-D)
In order to fully understand Spatial Disorientation, it is important to note how these sensory systems work together to determine the body’s relative motion and orientation. All of the above senses have specific minimum thresholds at which the particular sensation initiates a neural input perceived by the human mind. This means that below a certain signal intensity, inputs will not be perceived and therefore no action would occur. Fascinating studies have been conducted demonstrating that these thresholds and therefore one’s insensitivity to stimulus increases with inattention. It is easy to see how a pilot who is distracted or not aggressively monitoring flight instruments is at increased risk for dismissal of important sensory information. All of these systems also run the risk of adaptation and habituation, which means the response to persistent or repetitive stimuli decreases or possibly ceases altogether over time. This phenomenon allows Spatial-D to be intentionally reproduced in an aircraft, simulator, or spinning Barany chair in order to demonstrate how the mind can be easily fooled by constant angular motion. Which is exactly the scenario experienced during a prolonged banked turn.
Watch the below video as the US Navy student pilot points his thumbs in the direction of perceived rotation. After a certain amount of time under constant rotational acceleration, the fluid in the semicircular canals reaches an equilibrium and without the aid of vision to overrule his senses, he is unable to determine that he is still spinning.
NAVY PILOT BARANY CHAIR TRAINING
All of these different sensory systems also interact, further complicating study of this deadly condition. The vestibular sense seems to be suppressed in favor of visual dominance and enhanced by new, novel stimulatory sensations. This means that when vision is intact and unobstructed, the mind will favor vision’s spatial information over conflicting vestibular system data. If a pilot enters poor weather and vision is obstructed, however, the mind quickly reverses the suppressive effect on vestibular senses as spatial orientation becomes derived from these inputs. This can sometimes occur with disastrous results as the vestibular system is prone to very specific and reproducible errors when linear or angular accelerations are maintained for significant periods of time. Even on the ground at 1 G/0 knots, the various senses that provide humans with their spatial orientation can be prone to error. We know that humans require at least 2 of the senses described above to be operating correctly to maintain an accurate spatial and postural equilibrium. The Romberg Test, which is typically used by doctors to evaluate for stroke, examines the functioning of these systems by having the patient stand and close their eyes. If one’s proprioceptive or vestibular systems have been damaged due to brain injury, balance will not be maintained when visual input is eliminated.
CATEGORIES OF SPATIAL-D
There are variety of specific types of Spatial D that will be covered in detail on a future post. But Spatial-D is broadly divided into three categories:
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. This is a good thing as most cases of Type 3 Spatial-D result in controlled flight into terrain (CFIT) with survival only in the event of ejection.
Recent upgrades with Ground Collision Avoidance Technology (GCAT) such as the DoD’s Auto-GCAS is expected to save pilots experiencing unrecoverable Spatial D.
The following video demonstrates a Type 1 SD case followed by a re-creation of a fatal Type 3 SD case, both in the F-16 Fighting Falcon. Note that in the first case, the instructor pilot’s (IP) recommendations to “get on the round dials” possibly saves his wingman’s life as the disoriented pilot immediately corrects the attitude of his aircraft once his focus returns to inside the aircraft. This is likely due to the fact that his IP’s advice prompted him to transition from visually assessing his environment outside the cockpit in favor of trusting his internal flight instruments.
In summary, Spatial Disorientation remains a constant threat to general, military, and commercial aviation pilots alike. Globally, Spatial-D is thought to be the leading cause of mishaps in flight. This article provides a foundation for the anatomy, physiology and pathology for Spatial Disorientation and will be referred to in future articles on the topic. A list of types of Spatial D and how the above sensory systems make a pilot prone to this deadly syndrome can be found elsewhere.
1. Fundamentals of Aerospace Medicine (Ed. 4) by Jeffrey R. Davis (Editor), Robert Johnson (Editor), Jan Stepanek (Editor), Jennifer A. Fogarty (Editor).