Spatial disorientation Guide, Meaning , Facts, Information and Description
Spatial disorientation is a condition in which an aircraft pilot's perception of up-and-down (proprioception) does not agree with reality. While it can be brought on by disturbances to or disease within the vestibular system, it is more typically a temporary condition resulting from attempted flight into poor weather conditions with low or no visibility. Under these conditions the pilot may be deprived of an external visual horizon, which is critical to maintaining a correct sense of up and down while flying. A pilot who enters such conditions will quickly lose his spatial orientation if he does not have training in flying with reference to instruments. Approximately 80% of the private pilots in the United States do not have an instrument rating, and therefore are prohibited from flying in conditions where instrument skills are required. Unfortunately not all pilots abide by this rule, and approximately 40% of the NTSB fatal general aviation accident reports list continuation of flight into conditions for which the pilot was not qualified as either a contributing or proximate cause.During flight most of the senses are 'fooled' by centrifugal force, and indicate to the brain that 'down' is at the bottom of the cockpit no matter what the actual attitude of the aircraft. Only the inner ear and the visual sense provide data to the contrary. The inner ear contains rotational 'accelerometers,' known as the semicircular canals, which provide information to the lower brain on rotational accelerations in the pitch, roll and yaw axes. This system is imperfect, and errors develop in the brain's estimate of rate and direction of turn in each axis. Normally these errors are corrected using information from the visual sense, in particular an external visual horizon.
Once an aircraft enters conditions under which the pilot cannot see a distinct visual horizon, the drift in the inner ear continues uncorrected. Errors in the perceived rate of turn about any axis can build up at about 0.2 to 0.3 degrees per second per second. If the pilot is not trained for or is not proficient in the use of gyroscopic flight instruments these errors will build up to a point that control of the aircraft is lost, usually in a steep, diving turn known as a graveyard spiral. During the entire time leading up to and well into the maneuver the pilot remains unaware that he is turning, believing that he is maintaining straight flight.
The graveyard spiral usually terminates when (1) the g-forces on the aircraft build up to and exceed the structural strength of the airframe, resulting in catastrophic failure, or (2) the aircraft contacts the ground. In a 1954 study, the Air Safety Foundation found that out of 20 non-instrument-rated subject pilots, 19 of the 20 entered a graveyard spiral soon after entering simulated instrument conditions. The 20th pilot also lost control of his aircraft, but in another maneuver. The average time between onset of instrument conditions and loss of control was 178 seconds.
Spatial disorientation can also affect instrument-rated pilots in certain conditions. A powerful tumbling sensation (vertigo) can be set up if the pilot moves his head too much during instrument flight. This is called the Coriolis illusion. Pilot are also susceptible to spatial disorientation during night flight over featureless terrain.
This phenomenon was extensively reported in the press in 1999, after John F. Kennedy, Jr's plane went down during a night flight over water near Martha's Vineyard. Subsequent investigation indeed pointed to spatial disorientation as the likely cause.
Information from the following government documents is in the public domain.
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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. Genetically speaking, humans are designed to maintain spatial orientation on the ground. The three-dimensional environment of flight is unfamiliar to the human body, creating sensory conflicts and illusions that make spatial orientation difficult, and sometimes impossible to achieve. Statistics show that between 5 to 10% of all general aviation accidents can be attributed to spatial disorientation, 90% of which are fatal. It is important to know the difference between spatial orientation and airsickness.
Good spatial orientation on the ground relies on the effective perception, integration, and interpretation of visual, vestibular (organs of equilibrium located in the inner ear), and proprioceptive (receptors located in the skin, muscles, tendons, and joints) sensory information. Changes in linear acceleration, angular acceleration, and gravity are detected by the vestibular system and the proprioceptive receptors, and then compared in the brain with visual information (Figure 1, at right).
Most problems related to disorientation can be traced to the inner ear, a sensory organ about the size of an eraser on a pencil. It may well be the most well-protected organ in the human body, and for good reason. It's the key to our ability to balance when on the ground, or to remain oriented in space when we fly.
The inner ear is similar to a three-axis gyro. It detects movement in the roll, pitch, and yaw axes that pilots know so well. When the sensory outputs of the inner ear are integrated with appropriate visual references and spatial orientation cues from our bodies, there is little chance to experience disorientation.
The problem occurs when the outside visual input is obscured, and the seat-of-the-pants input is ambiguous. Then, you're down to just the output from the inner ear—and that's when trouble can start.
Fluid in the inner ear reacts only to rate of change, not a sustained change. For example, when you initiate a banking left turn, your inner ear will detect the roll into the turn, but if you hold the turn constant, your inner ear will compensate and rather quickly, although inaccurately, sense that it has returned to level flight.
Perhaps the most treacherous thing under such conditions is that the signals the inner ear produces—incorrect though they may be—feel right!
These sensory illusions occur because flight is an unnatural environment—our senses are not capable of providing reliable signals that we can interpret and relate to our position in three dimensions—without visual reference.
Spatial Orientation on the Ground
Spatial Orientation in Flight
Spatial orientation in flight is difficult to achieve because numerous sensory stimuli (visual, vestibular, and proprioceptive) vary in magnitude, direction, and frequency. Any differences or discrepancies between visual, vestibular, and proprioceptive sensory inputs result in a sensory mismatch that can produce illusions and lead to spatial disorientation. Good spatial orientation relies on the effective perception, integration and interpretation of visual, vestibular (organs of equilibrium located in the inner ear) and proprioceptive (receptors located in the skin, muscles, tendons, and joints) sensory information.Vestibular Aspects of Spatial Orientation
The inner ear contains the vestibular system, which is also known as the organ of equilibrium. About the size of an pencil eraser, the vestibular system contains two distinct structures: the semicircular canals, which detect changes in angular acceleration, and the otolith organs (the utricule and the saccule), which detect changes in linear acceleration and gravity. Both the semicircular canals and the otolith organs provide information to the brain regarding our body’s position and movement. A connection between the vestibular system and the eyes helps to maintain balance and keep the eyes focused on an object while the head is moving or while the body is rotating. The inner ear
Vision and the inner ear
Sensory illusions
As a result, when you finally level the wings, that new change will cause your inner ear to produce signals that make you believe you're banking to the right. This is the crux of the problem you have when flying without instruments in low visibility weather. Even the best pilots will quickly become disoriented if they attempt to fly without instruments when there are no outside visual references. That's because vision provides the predominant and coordinating sense we rely upon for stability.The Semicircular Canals
The semicircular canals are three half-circular, interconnected tubes located inside each ear that are the equivalent of three gyroscopes located in three planes perpendicular (at right angles) to each other. Each plane corresponds to the rolling, pitching, or yawing motions of an aircraft.Each canal is filled with a fluid called endolymph and contains a motion sensor with little hairs whose ends are embedded in a gelatinous structure called the cupula. The cupula and the hairs move as the fluid moves inside the canal in response to an angular acceleration.
The movement of the hairs is similar to the movement of seaweed caused by ocean currents or that of wheat fields moved by wind gusts. When the head is still and the airplane is straight and level, the fluid in the canals does not move and the hairs stand straight up, indicating to the brain that there is no rotational acceleration (a turn). If you turn either your aircraft or your head, the canal moves with your head, but the fluid inside does not move because of its inertia. As the canal moves, the hairs inside also move with it and are bent in the opposite direction of the acceleration by the stationary fluid (A). This hair movement sends a signal to the brain to indicate that the head has turned. The problem starts when you continue turning your aircraft at a constant rate (as in a coordinated turn) for more than 20 seconds. In this kind of turn, the fluid inside the canal starts moving initially, then friction causes it to catch up with the walls of the rotating canal (B). When this happens, the hairs inside the canal will return to their straight up position, sending an erroneous signal to the brain that the turn has stopped–when, in fact, the turn continues. If you then start rolling out of the turn to go back to level flight, the fluid inside the canal will continue to move (because of its inertia), and the hairs will now move in the opposite direction (C), sending an erroneous signal to the brain indicating that you are turning in the opposite direction, when in fact, you are actually slowing down from the original turn.
| The Leans. This is the most common illusion during flight and is caused by a sudden return to level flight following a gradual and prolonged turn that went unnoticed by the pilot. The reason a pilot can be unaware of such a gradual turn is that human exposure to a rotational acceleration of 2 degrees per second or lower is below the detection threshold of the semicircular canals. Leveling the wings after such a turn may cause an illusion that the aircraft is banking in the opposite direction. In response to such an illusion, a pilot may lean in the direction of the original turn in a corrective attempt to regain the perception of a correct vertical posture.
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Visual references provide the most important sensory information to maintain spatial orientation on the ground and during flight, especially when the body and/or the environment are in motion. Even birds, reputable flyers, are unable to maintain spatial orientation and fly safely when deprived of vision (due to clouds or fog). Only bats have developed the ability to fly without vision but have replaced their vision with auditory echolocation. So, it should not be any surprise to us that, when we fly under conditions of limited visibility, we have problems maintaining spatial orientation.
Central vision, also known as foveal vision is involved with the identification of objects and the perception of colors. During instrument flight rules (IFR) flights, central vision allows pilots to acquire information from the flight instruments that is processed by the brain to provide orientational information. During visual flight rules (VFR) flights, central vision allows pilots to acquire external information (monocular and binocular) to make judgments of distance, speed, and depth.
Peripheral vision, also known as ambient vision, is involved with the perception of movement (self and surrounding environment) and provides peripheral reference cues to maintain spatial orientation. This capability enables orientation independent from central vision and that is why we can walk while reading. With peripheral vision, motion of the surrounding environment produces a perception of self-motion even if we are standing or sitting still.Vision and Spatial Orientation
Central Vision
Peripheral Vision
| • Take the opportunity to experience spatial disorientation illusions in a Barany chair, a Vertigon, a GYRO, or a Virtual Reality Spatial Disorientation Demonstrator. |
| • Before flying with less than 3 miles visibility, obtain training and maintain proficiency in airplane control by reference to instruments. |
| • When flying at night or in reduced visibility, use the flight instruments. |
| • If intending to fly at night, maintain night-flight currency. Include cross-country and local operations at different airports. |
| • If only Visual Flight Rules-qualified, do not attempt visual flight when there is a possibility of getting trapped in deteriorating weather. |
| • If you experience a vestibular illusion during flight, trust your instruments and disregard your sensory perceptions. |
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