Spatial Disorientation


Spatial Disorientation can be defined from Encyclopædia Britannica [7] as “the inability of a person to determine his true body position, motion, and altitude relative to the earth or his surroundings.’’

The FAA Airline Transport Pilot knowledge test defined Spatial Disorientation as “pilots whom uses body sensations to interpret flight altitudes resulting in spatial disorientation” [Gleim & Gleim (2008 4)].

Spatial Disorientation is being defined by authors Green, Muir, James, Gradwell, & Green, [(1996 5)] as “a person suffering from illusions of orientations which some are caused by misinterpretation of visual information: difference in perception of orientation making a correspondingly inaccurate mental model.”

Spatial orientation defines “our natural ability to maintain our body orientation and/or posture in relation to the surrounding environment (physical space) at rest and during motion” [Melchor & Antuñano (2000 6)].

Theoretical frame

Spatial Disorientation is the mistaken perception of an individual’s position in relation to the motion relative to the earth. This effect usually happens to pilots and divers. In the context of aviation, this condition deprives the pilots’ visual references to maintain orientation. Fog, Darkness terrains, moonless nights etc created indistinct contrast which can rapidly cause spatial disorientation [Wynbrandt, (2004 10)]. In general, humans are designed to maintain spatial orientation on ground. Thus the flight environment is hostile and unfamiliar to the human body. This eventually creates sensory conflicts and illusions which allow spatial disorientation. Statistics show that between 5 to 10% of all general aviation accidents can be attributed to spatial disorientation and 90% of these accidents are fatal [Melchor & Antuñano (2000 6)]. Thus the following article will be directed in relations to aviation.

Spatial Orientation on Ground

Spatial Disorientation on ground are attributed towards the effectiveness of perception, interpretation of visual vestibular of equilibrium as well as the proprioceptive sensory information [Melchor & Antuñano (2000 6)]. Changes in linear accelerations, angular accelerations and gravity are all detected through the vestibular system and the proprioceptive receptors and then being compared to the visual information in the brain in order to determine the spatial orientation.

Spatial Orientation on Flight

In the aviation aspect, spatial orientations in flight are sometimes difficult to achieve due to various types of sensory stimuli which might vary in magnitude, directions and frequencies. Any differences or discrepancies which can be detected between the visual, vestibular and the proprioceptive sensory inputs into the brain might result in a sensory mismatch which eventually produces illusions and creates spatial disorientations [Melchor & Antuñano (2000 6)].

Mechanisms of Equilibriums for Spatial Orientation

There are 3 mechanisms of equilibriums in order to create a complete mental picture of orientation and provide balance to an individual [Wynbrandt, (2004 10)].

Visual Systems

Visual systems refer to our eyes which sense what we see. 90% of the information we use as references comes from the images captured from our eyes. It is the most reliable sensor of our senses as vision overrides conflicting sensations from all other sensory systems [Wynbrandt, (2004 10)]. In terms of Flying for pilots in visual meteorological conditions (VMC), 80% of the orientations are based on the orientation to the earth by references to the ground, sky and the horizon [Melchor & Antuñano (2000 6)]. Visual references that provide information about distance, speed, and depth of visualized objects include: [Wynbrandt, (2004 10)].

•Comparative size of known objects at different distances
•Comparative form or shape of objects at different distances
•Relative velocity of images across the retina in eyes. Nearby objects are perceived as moving faster then distant objects
•Interposition of objects
•Varying texture and contrast of objects at different distances
•Difference in illumination perspective of objects in lights or shadowing environment
•Differences in aerial perspective of visualised objects

Modes of Visual Systems

The visual systems have 2 modes of processing visual information.

Central/Focal Vision
This mode of processing visual information involves the identification of objects and the perception of colours. It is used for recognition and identification of objects [Melchor & Antuñano (2000 6)]. The images we perceived are stored in the memory in order for further comparison of their sizes in regards to our own position in order to achieve orientation.

In terms of flight during instrumental Flight Rules (IFR), the central vision allows pilots to acquire information from the flight instruments that is processed by the brain to provide spatial orientation information. During Visual Flight Rules (VFR), the central vision allows pilots to acquire external information in order to make judgements of distances, speeds and depths.

Peripheral/Ambient Vision
This mode of processing visual information involves with the perception of movement in individual and surrounding environment which provides peripheral reference cues to maintain spatial orientation [Melchor & Antuñano (2000 6)]. It primary role is to detect motion although it has poor acuity properties. This mode of processing is also responsible for orienting individuals in the absence of perception from vestibular apparatus [Wynbrandt, (2004 10)].

Types of Visual Illusions

Orientation by the visual systems requires perception, recognition and identification. Thus an individual must determine his/her position by understanding where referenced objects are in relations to his/her position. Visual illusions will occur when visual cues are reduced or obscurities are observed through many factors hindering vision [USAF 8]. In an aviation context, here are some typical visual illusions flight crews might encounter.

False Horizon Illusion
When flight crews encounter cloud formation as their only or distinct visual references, it can create an illusion in relations to the confused perception with the horizon or ground. Such illusion can be also created through flying over clouds (sloping cloud can have peripheral vision which might appear as horizontal), night flying over featureless terrain with ground lights that are indistinguishable from stars, or night flying with a pattern of ground lightings in starless skies. Confusion of ground lights and stars can lead to pilots distorting, manoeuvring the aircraft in unusual attitude to allow ‘ground lights’ being ‘above’ the aircraft as they perceive that the ground is part of the sky. Theses illusions can cause an individual to be spatially disorientated, causing pilots to fly the aircraft in a banked attitude [Melchor & Antuñano (2000 6)].

This illusion refers to the situation which might occur at night or in a dark environment. A stationary light against a dark background will appear to move if an individual fixates his/her concentration on the light for about 6 to 12 seconds. In flight, this can lead pilots to mistake the light for another aircraft which eventually he/she will attempt to manoeuvre the aircraft in order to avoid collision or to compensate for the perceived movement of the light [Green, Muir, James, Gradwell, & Green, (1996 5)].

Aerial Perspective/Depth Perception illusions
Such illusions are caused by the different widths, gradient of terrains. Such aerial perspective illusions are critical in aviation for flight safety during landings or approaches. Pilots’ mental model of approaches and landings are often developed through training. During approach, pilots recall a mental image of the expected relationships between the length and width of a typical runway landing image [USAF 8].

•Approach over flat terrain with UPSLOPING runway or a DOWNSLOPING TERRAIN with a flat runway might produce the visual illusion of a high-altitude approach. Such illusion distorts pilots’ responds as he/she might pitch the aircraft nose downwards in order to decrease the altitude, which might result in a Controlled Flight into Terrain (CFIT) accident.
•Approach over flat terrain with DOWNSLOPING runway or a UPSLOPING TERRAIN with a flat runway may produce the visual illusion of low-altitude approach. Such illusion may create responds by pitching the aircraft nose upwards, resulting in low-altitude stall or a missed approach.
•Visual illusion can be further created with either a narrow or long runway will produce high-altitude approach visual illusions.
•A wide runway might produce the visual illusion of a low-altitude approach

Black-Hole Approach Illusions
In aviation, this illusion has resulted in many air accidents. The black-hole effect occurs normally during the final approach at a starless or moonless night, over water or unlighted terrains towards a lighted runway (city airport) which horizon is not visible. While pilots are approaching a runway under such conditions with no lights prior to the runway, but with city lights or rising terrain beyond the runway, the black hole illusion will produce a high-altitude approach illusion. Pilots might then respond by lowering the aircraft glide slope which might result in CFIT accidents [Green, Muir, James, Gradwell, & Green, (1996 5)].

Vection/Relative Motion Illusion
This illusion happens when the brain interprets peripheral visual information making an individual confused in his/her situation. It refers to the falsely perceived self-motion in relation to the real motion of another object. For example, when stopped at a traffic light in a car, the car next to you edges forward slowly. Vection illusion might occur which an individual might perceive as he/she is rolling backwards and he/she will apply harder on brakes. Such illusion can happen while taxiing an aircraft at an airport [Melchor & Antuñano (2000 6)].

Structural illusions
Structural illusions are causes by heat waves, rain, snow or visual obscurants. A straight line may appear to be curved when viewed through such visual obscurants [Wynbrandt, (2004 10)].

Reversible Perspective Illusions
At night, such illusions may allow pilots to perceive that an aircraft maybe appearing to be going away but it is actually approaching. Such illusions are usual observed during flying in parallel courses.

Crater Illusion
This illusion occurs during landings for pilots at night, with the landing lights to far under the nose of the aircraft. Thus it will create an illusion of landing into a crater [USAF 8].

Flicker Vertigo
Causes through lights travelling pass rotor blades of helicopters or turbo-propeller aircrafts which will result in drastic physical deterioration resulting fatal accidents.

Whiteout Effect
Dust or snow covered terrain obscuring visual cues will result in spatial disorientations for pilots [Gleim & Gleim (2008 4)].

Vestibular Systems

The vestibular system which is also known as the kinaesthetic senses is human secondary positioning systems consisting of motion and gravity-sensing organs, which provides spatial orientation. The systems are located in each of our inner ear, each providing data to the brain with the information needed to maintain one’s orientation and balance [USAF 8]. However, vestibular system can be compromised by factors such as sickness, dizzy or nauseous etc as the internal gyros do not function properly. This function is to supplement vision for maintaining one’s orientation [Wynbrandt, (2004 10)].

Two Structures of each Vestibular Apparatus

Each Vestibular apparatus has two organs which collects information to the brain, maintaining orientation.

Semicircular Canals
The semicircular canals each have three perpendicular tubes containing fluids and thousands of sensory hair. As the body moves, the motion of the fluid in each canal provides the brain with data such as roll, pitch or yaw. However, due to its unique design, there are several limitations whereas wrong data might be recorded by the sensory hairs in each canal. When aircrafts makes a turn, the inertia of fluid moves in the opposite directions relatively to the sensory hairs, thus we interpret the turn and direction, but as the turn continues, the fluid catches up which might be often interpreted by the sensory hair as the turn has ceased. Therefore, prolong turning rate might result in a false sensation of not turning. Turning at 2 degrees per second are proven to insufficiently stimulate the fluid in the canals, thus without visual information, it is possible that spatial disorientation had occur [Green, Muir, James, Gradwell, & Green, (1996 5)].

Otolith Organs
Theses organs are small sacs which are in the semicircular canals. They are embedded with the sensory hair and contained ‘otoliths’ which are gelatinous membrane with chalklike crystals [Green, Muir, James, Gradwell, & Green, (1996 5)]. As an individual moves, the movement of the membrane against the sensor hairs will register gravity. They are simulated by gravity and linear acceleration but they can only sense a change in speed but not in direction [USAF 8].

Types of Vestibular Illusions

Vestibular illusions occur when either the semicircular canals (somatogyral illusions) or the Otolith organs (somatogravic illusions) received wrong data/inputs as a result of the environment. Such illusion might be overwhelming and are the greatest danger of spatial disorientation.

Somatogyral Illusions

The Leans
This illusion is based upon the principle that the sensory hair cells in the semicircular canals will extinguish a signal after approximately 20seconds which will lead to an individual believing that they are at level despite being at a banking angle or a turn [Green, Muir, James, Gradwell, & Green, (1996 5)]. In aviation, this is the most common form of spatial disorientation which results a pilots’ failure to detect their motion. If a pilot enters a bank slowly, or prolong its turning time till fluid in the semicircular canals are stabilised, the aircraft might already be straighten and levelled but the motion in the pilot’s semicircular canals will still perceive that the aircraft was banking in the opposite direction. Thus this might result in the pilot abrupt control movements in order to compensate with the illusion [Wynbrandt, (2004 10)].

Graveyard Spin & Spiral
This illusion can occur when a pilot is engaged in prolong constant, coordinated turn, creating an illusion whereby the pilot might perceive that they are not turning. Thus the pilot either increases the turn angle or increases the airspeed in order to achieve what him/her desire. Thus with any bank rate of less then 2degrees, the pilot may not feel it but the aircraft might be already engaged in a spiral downward turn. As the aircraft spiral downwards, descent increases together with the increase in banking angle. As the pilot notice the loss of altitude, the naturally corrective action of pulling back on the controls to climb will further deteriorate the situation [FAA (2007 3)].

Coriolis illusion
This illusion is based on the cross-coupling effect when two or more semicircular canals are simultaneously stimulated. Sudden abrupt movement of head triggers such illusions [FAA (2007 3)].

Somatogravic Illusions

Oculogravic or also known as Somatogravic illusion
This illusion can be caused by the rapid acceleration such as takeoff which stimulates the otoliths organs in the same way as tilting the head backwards [FAA (2007 3)]. This action creates the aircraft being nosed-up especially in situations without any visual references (CAT III Takeoff). The upward movement of the eyes during the rapid acceleration leaves the eyes lagging, looking up relatively to the aircraft. Thus the sensation creates such illusions [Melchor & Antuñano (2000 6)].

Elevator illusion
This illusion is created with a sustained forward acceleration (Fighter Jets on Aircraft carrier with catapult launches) which the otoliths organs are stimulated. This illusion causes a nose up sensation creating an urge for pilots to push the control stick forward into a dive. Thus in order for fighter pilots to prevent themselves for this illusion, they took off on aircraft carriers with hands placed on handles at the top of their seats [USAF 8].

Nystagmus (Vestibulo-ocular Interaction)
This simply refers to the involuntary rapid oscillations of the eyes in a horizontal, vertical or rotary direction which will create spatial disorientation [USAF 8].

Inversion Illusion
This is an illusion of tumbling backwards which was caused by an abrupt change from climb to straight-level flight. The abrupt change can excessively stimulate the sensory organs for gravity and linear acceleration which results in such spatial disorientation [USAF 8].

Somatosensory or Proprioceptive System

This system comprises of the nerves in skins, muscles, joints, internal organs and hearing. It allow individual to be aware of its position, weight and changes in the equilibrium. As the nerve senses pressure differentials, this system remains relatively unnoticed while on ground. But while flying, pilots can feel the G-forces and pressure as the inertia of the body reacts to the motion of the aircraft [USAF 8]. These sensations are mostly acutely felt when the body and the aircraft meets which is the pilot’s seats. The term Seats-of-the-pants strictly refers to pilots correctly interpreting these sensations [Melchor & Antuñano (2000 6)].

FAA’s Prevention Actions for Spatial Disorientation

The Aeromedical Education Division of the FAA Civil Aerospace Medical Institute [Melchor & Antuñano (2000 6)] and the FAA Instrument Flying Handbook [FAA (2007 3)] recommended the following actions to minimise the risk of spatial disorientation for pilots.

•Understand illusions and remain constant alert for such perception
•Obtain training and maintain your proficiency in aircraft control by reference to instruments.
•When flying at night or in reduced visibility, use and rely on your flight instruments.
•Always obtain and understand the latest preflight weather briefings.
•Study and become familiar with unique geographical conditions where flight is intended.
•Do not attempt visual flight when there is a possibility of being trapped in deteriorating weather.
•If you experience a visual illusion during flight (most pilots do at one time or another), have confidence in your instruments and ignore all conflicting signals your body gives you. Accidents usually happen as a result of a pilot's indecision to rely on the instruments.
•If you are one of two pilots in an aircraft and you begin to experience a visual illusion, transfer control of the aircraft to the other pilot, since pilots seldom experience visual illusions at the same time.
•Ensure that when using outside visual references, they must be reliable and fixed infrastructures/lights on the earth.
•By being knowledgeable, relying on experience, and trusting your instruments, you will help keep the skies safe for everyone.
•Avoid sudden head movement in particular to during takeoffs, turns and approaches to landings.
•Physically healthy will reduce the risk for spatial disorientation

Supporting evidence

Spatial disorientation has been a causal factor for many aviation accidents. A study carried out by Bellenkes, Bason & Yacavone (1992 [1]) determined that partial disorientation as a causal factor for all 33 class A mishaps (1980-1989) they analysed. It was found that Type I spartial disorientation was common in helicopter pilots operating at night and Type II was common in jet pilots perating during day time. Clark and Rupert (1992 [2]) found that this spartial disorientation was due to misperception of visual, proprioceptive or vestibular cues.

Refuting evidence

Way forward (to do list)

1. Bellenkes, A., Bason, R. & Yacavone, D. W. (1992). Spatial disorientation in naval aviation mishaps - A review of class A incidents from 1980 through 1989. Aviation Space and Environmental Medicine, 63, 2, 128-131.
2. Clark, J. B. & Rupert, A. H. (1992). Spatial disorientation and dysfunction of orienation equilibrium reflexes - Aeromedical eveluation and considerations. Aviation Space and Environmental Medicine, 63, 10, 914-918.
3. Federal Aviation Administration (FAA). (2007).Instrument Flying Handbook. USA: Jeppesen, Boeing Company
4. Gleim, I. N. & Gleim, G. W. (2008). ATP Airline Transport Pilot FAA Knowledge Test. USA: Gleim Publications.
5. Green, R. G. Muir, H. James, M. Gradwell, D. & Green, R. L. (1996).// Human Factors for Pilots (2nd Ed).// U.K: Ashgate.
6. Melchor J. & Antuñano, M.D. (2000). Spatial Disorientation: Seeing is not Believing. In Medical Facts for Pilots. FAA Civil Aerospace Medical Institute. Publication AAM-400-00/1
7. Spatial disorientation. (2008). In Encyclopædia Britannica. Information Retrieved on October 07, 2008, from Encyclopædia Britannica Online website:
8. United States Air Force. Flight Surgeon Refresher Course-Spatial Disorientation. USAF publication FSRC-304. US Army School of Medicine.
9. Wickens, C. D. & Hollands, J. G. (2000).Engineering Psychology and Human Performance. Upper Saddle River, USA: Prentice-Hall Inc.
10. Wynbrandt, J. (2004). Spatial Disorientation, Confusion that Kills. In AOPA Air Safety Foundation, //Safety Advisor Physiology Safe Pilots Safe Skies Publication NO: 1 08/04.

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