Spatial Disorientation in Aviation

Spatial Disorientation

T R****** 9/30/2014

Introduction Spatial awareness, is defined as the body’s innate ability to perceive and maintain its orientation with respect to the surrounding environment both in motion and at rest. As a general rule human beings have adapted to maintain orientation while on the ground (SKYbrary, 2013). Within an aircraft environment, a pilot will deal with environmental sensations induced by three planes of motion. As would be expected this is unfamiliar to the human body, and as a result, this unfamiliar motion can in turn induce illusions, or sensory conflicts, that make maintaining spatial orientation difficult, if not impossible. According to the FAA (n.d) advisory publication “Spatial Disorientation”, approximately 510% of aviation accidents have been attributed to some form of spatial disorientation, with 90% being fatal. In flight it can be challenging to form a detailed picture of your position in regard to your surroundings due to the vast numbers of sensory stimuli and the large variance in magnitude, frequency and direction (SKYbrary, 2013). When we (as pilots) receive what we perceive to be discrepancies between the information given to us by the visual, proprioceptive and vestibular systems we suffer what are called illusions, and it is these illusions that cause disorientation (PilotFriend, 2014). The key to effective spatial orientation is heavily reliant on proper perception, interpretation and integration of the sensory information provided by the visual as well as vestibular and proprioceptive systems (Stott, 2013). As a general rule humans trust their vision implicitly, and rely on vision for approximately 80% of orientation information. This behaviour renders pilots susceptible to a myriad of visual and physical illusions, particularly during takeoff and landing. Even in VFR conditions, pilots must monitor the aircraft instruments to maintain their position in space, in conjunction with other important details such as airspeed and attitude. The aircraft’s instruments are of no use if the pilot doesn’t ‘believe’ the information displayed. This seems like a simple concept but issues arise when pilots feel compelled to believe what their eyes are telling them rather than ‘accepting’ data from their instruments (SKYbrary, 2013). This concept becomes even more important when flying in IMC (instrument meteorological conditions) where there is little/no visual reference. Without visual reference our natural sense of spatial orientation becomes reliant on our vestibular and proprioceptive systems, and commonly this is when illusions manifest themselves.

This is why pilots who wish to fly under instrument conditions, require significant additional training to reduce dependence on their “internal” senses when they are at their most susceptible to illusions (SKYbrary, 2013). Disorientation presents itself in two ways; The first is a sense of confusion, usually in regard to aircraft attitude, when conflicting sensations are coupled with deteriorating visual conditions. The second occurs when the pilot perceives everything to be as expected only to come to the realisation that the aircraft has entered an undesired aircraft state. Once a pilot is said to have made an error in judgment that leads to one of these undesired aircraft states, the pilot is said to be disoriented. The use of the term “illusion” is recurrent throughout all literature about spatial disorientation, and it is the nature of such an illusion that forms the basis for the classification of in-flight events (Stott, 2013).

The Physiology of Spatial Awareness and Disorientation Many aircraft accidents have been attributed to visual illusions and spatial disorientation with their consequence being most prominent during night operations or in instrument meteorological conditions. Visual illusions manifest as a distortion of the visual information received by the pilot that may lead to misinformed decision making and poor situational awareness. Spatial disorientation transpires when the pilot’s perception of their position and situation is grossly different to the reality, usually due to conflicting sensations produced by the vestibular and proprioceptive systems (Newman, 2007). Spatial Disorientation, or SD, can be categorised into three groups; Type 1 – Unrecognised This is considered to be the most dangerous form of SD, as the pilot is unaware of the problem at hand and therefore will not take corrective action to rectify the situation. The pilot believes what they see or “perceive to see” matches with their other senses. An example of this phenomenon might be as follows; on an approach to land on a narrow strip, the pilot would believe that they are higher than they actually are, causing them to undershoot the approach (LeCompte, 2008).

Type 2 – recognised A pilot may recognise that there is something wrong, but not necessarily realise it is spatial disorientation. The issue may be perceived as an equipment or instrument failure. The pilot may still believe their vestibular system over the aircraft indications and may not correct the aircraft state. Type 3 – Incapacitating As in type 2, the pilot has recognised there is a problem, but due to the extremity of the event or confusion, cannot reorient through use of instruments or visual cues. The only way to relieve the situation is to shift control from the disoriented pilot – which is not possible in single pilot operations (Newman, 2007).

Visual Illusions The visual system consists of central and peripheral vision. Vision is the dominant sense for orientation when good visual cues are present, and attention to the other senses is easily and often suppressed. It is important to note that we use our central vision for perceiving depth and distance, and that it is our peripheral vision that provides us with the subconscious orientation and motion information. It is the peripheral vision that is often paired with our vestibular sensations to provide a complete indication of relative position in the surrounding environment (Av Med, 2011). Given the visual system provides humans with up to 80% of orientation information, when this system suffers from an illusion onset, it can be a very powerful threat (Stott, 2013). Some of the most common visual illusions experienced by pilots include false horizons, illusions of perspective, autokinesis and the black hole effect. False Horizons also known as a sloping cloud horizon occurs in a number of situations, most commonly due to haze, clouds or mountainous terrain, in poor visual conditions. If not using the artificial horizon as the primary attitude indication during flight, pilot may misidentify the horizon accordingly. This could lead to setting an unwarranted climbing or descending attitude, the wrong power setting, or potentially unobserved banking attitudes. The risk with this illusion is not only the risk of collision with other traffic, but also with terrain (Av Med, 2011).

Perspective illusions, are a misinterpretation of aircraft position relative to a given runway. Pilots, through practice, develop recognition of what is called an approach profile. This profile will usually correspond with the common fields they visit. Any change in length, width, gradient and surrounding terrain may distort this “approach profile”. For example, on final approach for an up sloping runway, the pilot may perceive that they are too high on their profile and then lower the nose to compensate. This could lead to a runway undershoot or hard landing situation. Conversely a down sloping runway may cause a pilot to believe that they are low on the approach, this would likely result in flaring too early and thus stalling and/or performing a hard landing (Newman, 2007). Another illusion could occur on a flat narrow runway surrounded by down sloping terrain. The pilot will likely perceive that they are on a high approach profile and will correct by lowering the nose, again this can result in an undershot or hard landing. A black hole approach, common during night operations, may occur when the only visual reference is the runway lighting. A worse scenario would occur on up-sloping terrain, potentially with bright lights from a city or town at the upwind end of the runway. This can cause the pilot to misinterpret the approach as ‘high’, and erroneously correcting the perceived state by further lowering the nose, risking undershooting of the runway (Newman, 2007). Autokinesis refers to the perceived movement of a stationary object on a visually indistinct background. This may often be a star on a dark night or a light from a proximal aircraft. The light may be seen as rotating in either a circular or linear plane and can make it difficult to identify actual aircraft movements. This is due to the relaxation of the cillary muscles in the eye and can be corrected by momentarily adjusting the pilots focus to different objects including the instruments or external aircraft structures (Av Med, 2011). Vestibular illusions The human vestibular system, essentially monitors and thereby provides the source of our perceived sense of balance and feedback, and is provided by the two balance organs in each of our ears, the otolith organs and the semicircular canals. The semicircular canals are three tiny interconnected gyroscopes oriented at right angles to one another within the inner ear. Their role is to sense angular acceleration, meaning it provides us with our orientation in the pitch, roll and yaw planes of motion.

The important limitation to be aware of with this organ is that, it can only sense angular acceleration above 2 degrees per second. Therefore any movement below this threshold may, and usually will be, imperceptible – yet consequences can be catastrophic (Stott, 2013).

(PilotFriend, 2014) Disorientation experienced with respect to the semicircular canals are called ‘Somatogyral Illusions’. The manifestation of somatogyral illusion is most likely to occur when flying in conditions of poor or non-existent external visual reference, and is known to induce a false sense of rotation. The phenomena that fall into this category include “The Leans”, the “Coriolis Effect”, and the “Graveyard Spin or Spiral” (FAA, n.d). Onset of ‘The Leans’ is the illusion of banking when the aircraft is straight and level. It is the most common of all vestibular illusions. It is normally not dangerous, as it occurs after a correction has been made to aircraft attitude following an undetected bank. Once the aircraft is returned to level, the pilot feels the sensation of a bank in the opposite direction and may tilt their head in the direction of the perceived turn to reduce the sensation (SKYbrary, 2013). The Coriollis Illusion occurs when two or more of the semicircular canals are stimulated simultaneously, this can occur if the pilot moves their head rapidly when looking at their maps, overhead panel or picking up a pencil they may have dropped. This illusion induces the uncomfortable sensation of uncontrollably tumbling. Accidents can occur due to this illusion, due to the inability to distinguish between yaw, roll and pitch (Newman, 2007).

The graveyard dive is an extremely dangerous phenomenon and usually occurs as a result of ‘the leans’ or another form of spatial disorientation. If an aircraft slides into an undetected bank attitude and is not corrected, the nose will eventually pitch downward increasing the airspeed. Once recognised, the pilot, who has until this point believed that the aircraft was straight and level, will instinctively pull back on the controls to reduce airspeed and pitch up, however as the aircraft will be in a banked attitude, this back pressure will only increase the bank angle and therefore the intensity of the dive. Unless recognised and corrected immediately, the aircraft will almost definitely plunge into the ground or sea (Av Med, 2011). (This is what is believed to be the cause of loss of JF Kennedy Junior and his two passengers in 1999.) The Otolith organs are associated with what is called the “Somatogravic Illusion” There are two Otolith organs in each ear, they are made up of the Saccule and Utricle. The Utricle sense motion in the horizontal plane and the Saccule works in the vertical plane. Together these organs work as linear accelerometers, and under standard conditions the organ in the vertical plane is responsible for monitoring the earth’s gravitational field (PilotFriend, 2014). The term Somatogravic illusion, is the association of linear acceleration as motion in the pitching plane. For example on takeoff , the forward acceleration may be interpreted as an exaggerated pitch up or climbing motion and conversely deceleration in straight and level can be misconstrued as a descending motion. These misconceptions can be extremely dangerous especially in poor visual conditions or at night. Additionally when a high performance aircraft levels off after a climb the high relative airspeed coupled with the nose down attitude can produce the sensation of inverted flight, if the pilot pitches down to compensate for this “apparent attitude” the aircraft may enter a dive, and if not corrected, can be extremely dangerous (FAA, n.d). Early in US Air Force operations, there was a recurrent problem of fighter pilots flying into the ocean upon takeoff from aircraft carriers. It is believed to be due to this illusion. Upon take off at night, the acceleration experienced by pilots, also felt like an apparent pitch up, to combat this sensation, pilots would in turn pitch the aircraft down to “correct” the perceived attitude change, and end up diving into the sea. This phenomenon occurs due to the significant change in ‘G’ force experienced by these

organs. This change in force is not normally experienced when on the ground and the vestibular system is not adapted to distinguish between pitch and acceleration (LeCompte, 2008). Proprioceptive illusions The proprioceptive system uses a variety of receptors found in the skin, joints and muscles to be able to provide information on the relative position of limbs and the surrounding environment without visual references. It aids with balance and can tell us if we are standing sitting or moving, however its role in general spatial orientation is limited. This system on its own doesn’t provide much information, for example it cannot differentiate between straight and level flight and a balanced turn, however when coupled with the vestibular or visual systems, it helps provide a complete picture of physical and spatial orientation. There are no specific proprioceptive illusions per say, but this sensory system is commonly associated with the aforementioned somatogravic illusions (Av Med, 2011).

Spatial Disorientation in Aviation History There are numerous accounts of ‘accidents’ throughout the history of aviation, however it is these ‘accidents’ that have been investigated, analysed and used to produce stricter, more effective regulation, more targeted training and greater awareness. This in turn has led to aviation becoming an inherently safer industry. One of the events that served to change the future of aviation and the training of pilots was the tragic death of the high profile JF Kennedy Junior, and his two passengers in 1999. The significance of this particular incident is that the concluded cause was pilot error ‘as a result of spatial disorientation’. According to the NTSB report JF Kennedy Junior was a qualified private pilot with over 310 hours, and multiple endorsements, he had flown this particular route numerous times, both with and without an instructor and at least 5 times at night. Although having completed the theory examination Kennedy was not an instrument rated pilot (Airsafe.com, 2009). On the night of the accident, the conditions were considered to be VMC (conditions suitable for flight under visual flight rules) however there had be reports of hazy conditions and visibility down to 4nm. Originally planning to leave before EOD, Kennedy and his passengers were delayed and

ended up departing later than planned (Airsafe.com, 2009). The first threat that presents itself is a potentially ‘rushed’ flight crew. With the forecast of haze the pilot should have been aware of the potential of the false horizon illusion. According to radar analysis the aircraft activity appeared relatively normal until reaching approximately 34 miles to the west of their destination, Martha’s Vineyard Airport. At this point in the flight the first signs of potential disorientation manifest while crossing a 30 mile body of water. The aircraft was documented to have begun a varied descent between 400-800fpm, this in itself is not considered unusual however upon reaching 7 miles from the shoreline, the aircraft entered a right turn and stopped descending at approximately 2200ft and consequently climbed back to 2600ft followed by entry into a left turn (Airsafe.com, 2009). This could indicate an unintentional descent and turn; this may have been the beginning of the leans and a subsequent graveyard dive. While in the left turn the aircraft then began a more rapid descent reaching 900fpm. From here the radar indicated the aircraft then entered another right turn while still descending, unfortunately, this turn was accompanied by a significant increase in rate of descent to in excess of 4700fpm and the aircraft proceeded to strike the water in a nose down attitude. The NTSB determined the cause of the accident as pilot error as a result of spatial disorientation with aircraft manoeuvres consistent with attempted recovery and subsequent entry into a grave yard dive as a result of the leans. Other contributing factors we identified, including haze and the dark night. It has been suggested that JF Kennedy Junior may have recovered from the beginnings of two graveyard dives before the third brought the aircraft down into the ocean (Airsafe.com, 2009). This example is certainly not the only event that has had an impact on aviation operations and regulation, but it is one of the most high profile, and clearly demonstrates the seriousness of disorientation in flight.

Prevention As previously mentioned spatial disorientation is to blame for approximately 5-10% of all aviation accidents, this may not seem particularly significant, however considering 90% of those incidents were fatal, it is definitely an area of particular concern. Although not entirely preventable, through education and specific and rigorous training, the number of these incidents can continue to decline (Stott, 2013). It is important to remember that the sensory misinformation produced by these illusions are predictable, and only occur due to the normal functioning and associated limitation of these systems. As humans are not adapted for flight. These shortcomings can be expected in unusual conditions such as acceleration, turns and fluctuating G loads (Newman, 2007). With these limitations being accepted, training programs have been developed to redirect pilot attention to their instruments. Factors such as proper training, simplistic aircraft cockpit design, and good health all contribute to reducing spatial disorientation. Any pilot irrespective of age, gender and experience can suffer from spatial disorientation and therefore must be made aware of the hazards associated with these phenomena, in order to mitigate the inherent risks (SKYbrary, 2013). Simple rules, need to be adopted by all pilots – being aware of ones limitations and not trying to fly under both VMC and IMC on the same flight (CavalryPilot, 2006). Simplifying flight procedures, and appropriate preparation, is the way to effectively decrease cockpit workload without detracting from overall crew performance (PilotFriend, 2014). All these methodologies, and many more, may be adopted in both the operational requirements, and training programs, of both the private and commercial operator, to ensure the risks associated with spatial disorientation will continue to be minimised and effectively managed.

Conclusion Loss of control, or controlled flight into terrain, is inevitable if corrective action is not applied upon the onset of spatial disorientation. Unfortunately becoming disoriented is inherently inevitable at some stage in a pilot’s career. However accidents are avoidable if the appropriate measures are taken. Educational remediation to physiological shortfalls may help flight crew identify and rectify issues associated with spatial disorientation before they become an issue and the aviation industry can continue to become a safer environment as a result. Despite the advancement in aircraft instrumentation and display mechanisms, there will always be a time where pilots question what the aircraft system is telling them due to the conflicting messages their internal instruments are relaying (SKYbrary, 2013). No one is impervious to these sensations, therefore ongoing crew education targeting the risks associated with spatial disorientation and how to recognise, recover or avoid is of utmost importance in maintaining flight safety.

References 

Airsafe.com, 2009. Airsafe.com. [Online] Available at: http://www.airsafe.com/events/celebs/jfk_jr.htm [Accessed 28 September 2014].



Av Med, 2011. Aviation Medicine. [Online] Available at: http://www.avmed.in/2011/04/spatial-disorientation-vestibular-illusions/ [Accessed 28 September 2014].



FAA, n.d. FAA.gov. [Online] Available at: http://www.faa.gov/pilots/safety/pilotsafetybrochures/media/SpatialD.pdf [Accessed 28 Sepetember 2014].



LeCompte, T., 2008. The Disorient Express. AIR & SPACE MAGAZINE, September.



Newman, D., 2007. An overview of spatial disorientation as a factor in aviation accidents and incidents, Canberra: Australian Transport Safety Bureau.



PilotFriend, 2014. Aviation Medicine - PilotFriend. [Online] Available at: http://www.pilotfriend.com/aeromed/medical/spat_disorientation.htm [Accessed 28 September 2014].



SKYbrary, 2013. Skybrary.Aero. [Online] Available at: http://www.skybrary.aero/index.php/Spatial_Disorientation [Accessed 29 September 2014].



Stott, J., 2013. Orientation and disorientation in aviation. [Online] Available at: http://www.extremephysiolmed.com/content/2/1/2# [Accessed 28 September 2014].