Spatial Disorientation - FAASafety.gov

1 Spatial DisorientationConfusion that KillsAOPA Air Safety FoundationSAFETY ADVISORP hysiology No. 1 Pilots deprived ofvisual referenceswhile flying canquickly lose controlof the aircraft and succumb to one ofgeneral aviation sbiggest deprived ofvisual referenceswhile flying canquickly lose controlof the aircraft and succumb to one ofgeneral aviation sbiggest Side UpWe humans are VFR-only creatures. The senses we useto maintain our balance and know which end is up are completely unreliable when our bodies are inmotion without visual reference to the world aroundus. Pilots deprived of visual references while flying canquickly lose control of the aircraft and succumb to oneof general aviation s killers: Spatial Disorientation : What Is It? Spatial Disorientation is the mistaken perception ofone s position and motion relative to the earth. Anycondition that deprives the pilot of natural, visual refer-ences to maintain orientation, such as clouds, fog,haze, darkness, terrain or sky backgrounds with indis-tinct contrast (such as arctic whiteout or clear, moon-less skies over water) can rapidly cause Spatial disorien-tation.

2 Pilots can compensate by learning to fly byreference to their instruments. But a malfunction offlight instruments, such as a vacuum failure, in condi-tions of reduced visibility can also end in Spatial disori-entation, with the same lethal the physiology and dangers of Spatial disorienta-tion are taught during primary and instrument flighttraining, general aviation pilots still have misunder-standings about what it is and how to deal with it. Andthe accidents it causes continue to claim the lives oftoo many pilots and passengers every year. Maintaining OrientationAre you sitting up or lying down? Leaning one way oranother? Three sensory systems give us the informationwe use to maintain our equilibrium and determinewhere we are and how we re oriented:Safe Pilots. Safe Skies. Pg. 2 Visual system Our eyes, which sense position based on what we see. Vestibular system Organs found in the inner ear that sense position by the way we re balanced.

3 Somatosensory system Nerves in the skin, muscles, and joints, which, along with hearing, senseposition based on gravity, feeling, and how each of these systems operates helpsexplain how Spatial Disorientation develops, and howto minimize your chances of experiencing SystemNinety percent of the information we use for point ofreference comes from our eyes. The most reliable ofour senses, vision overrides conflicting sensations fromour other systems. When we fly in visual meteorologi-cal conditions (VMC), our vision enables us to keep theairplane properly oriented to Earth by reference to theground, sky, and horizon. Such is its power that we rerarely aware when our brain receives conflicting signalsfrom other systems. Vision is relatively reliable, but it sprone to illusions, mistakes in processing or interpretingwhat we see, that can result in Spatial Disorientation . Vestibular SystemThe vestibular system, also called the kinesthetic sens-es, is our secondary positioning system, consisting ofmotion- and gravity-sensing organs.

4 The system isredundant; there s one in each inner ear, each capableof providing the brain with all the information neededto maintain balance. They can, however, be compro-mised by several factors: when sick, inebriated, hungover, dizzy, or nauseous, our internal gyros don t func-tion properly. Also, this system can only supplement,not replace, vision for maintaining orientation whileairborne. Each vestibular apparatus has two structures:semicircular canals and otolith organs. Semicircular canalsThe semicircular canals each have three perpendiculartubes containing fluid and sensory hairs. As the bodymoves, the motion of the fluid in the canals providesthe brain with roll, pitch, and yaw information. Thissystem can even substitute for sight while on theground; if you close your eyes, you can still walk, orsense whether you re upright or lying down. However, there are some limitations, such as when aturn commences in the air, the inertia of the fluidmoves in the opposite direction relative to the sensoryhairs, and we correctly interpret the turn and its direc-tion.

5 But if the turn continues, the fluid catches up, cre-ating the sensation that the turn has ceased. Therefore,a prolonged constant rate turn results in the false sensa-tion of not turning at all. When the turn finally doesstop, due to inertia the fluid continues moving, creatingthe sensation of a turn in the opposite direction. Addi-tionally, any bank rate of less than two degrees per sec-ond is insufficient to stimulate the fluid in the canals,and will not be felt. Considering that a standard rateturn is three degrees per second, you can understandhow, without visual reference , it s possible to enter abank that becomes progressively steeper while feelingthat the aircraft is flying straight and organsThe otolith organs are small sacs at the base of thesemicircular canals. They are embedded with sensoryhairs and contain a gelatinous membrane with chalk-like crystals called otoliths. As the head or bodymoves, the movement of the membrane against thesensory hairs registers gravity.

6 The forces of acceleration and deceleration also stimu-late the otoliths and, without visual reference , the bodycan t tell the difference between the inertial forcesresulting from acceleration and the force of , acceleration may give the sensation of tiltingbackwards. Deceleration may give the perception ofpitching SystemAlso called the proprioceptive system, this system iscomprised of nerves in the skin, muscles, joints, andinternal organs, along with hearing. The nerves sensepressure differentials. This system remains relativelyunnoticed on the ground. But while flying, pilots canfeel changes in G-forces and pressure as the inertia ofSafe Pilots. Safe Skies. Pg. 3their bodies reacts to the motion of the airplane. Thesesensations are most acutely felt where the body andthe airplane meet, namely on the seat, and the abilityto correctly interpret these sensations is the source ofthe term seat-of-the-pants flying.

7 Our binaural hearing can determine our position rela-tive to a sound source. In the air our hearing can alsoidentify conditions such as an overspeeding propeller ,air rushing against the airframe, or an engine suddenlygoing IllusionsAll three sensory systems are prone to errors. Insome cases we may have the illusion of beingstraight and level when we re almost inverted. Orwe may be convinced we re tumbling end over endwhen we re straight and level. The following aresome of the most common illusions affecting pilotsof fixed-wing aircraft that can result in Spatial disori-entation. Visual IllusionsFalse Horizon When the only or most distinct visualreference is a cloud formation, it can be confused withthe horizon or the ground. A sloping cloud deck thatextends into a pilot s peripheral vision will appear to behorizontal. Likewise, a cloud bank below the aircraftthat is not horizontal to the ground may appear to behorizontal.

8 These illusions cause the pilot to fly the air-craft in a banked attitude. Confusing Ground and Star Light At night, groundlights can be confused with stars. This can lead pilots tomaneuver the aircraft into an unusual attitude in an effortto put the ground lights above them. In areas withsparse ground lighting, isolated lights can also be mistak-en for stars, which can make the aircraft appear to be in anose-high attitude or have one wing low. When overcastconditions block any view of stars, unlighted areas of theterrain can appear to be part of the sky. Autokinesis At night, a stationary dim light against adark background will appear to move if a pilot visuallyfixates on the light for about six to 12 seconds. This canlead pilots to mistake the light for another aircraft, andto attempt to maneuver the aircraft to compensate forthe perceived movement of the IllusionsIn the absence of visual reference , we rely on our vestibu-lar system to keep us oriented.

9 But as previously explained,this system is unreliable when in motion. Therefore, theseillusions create the greatest danger of Spatial Leans This is the most common form of spatialdisorientation. It results from a pilot s failure to detectangular, or banking, motion. If a bank is entered slowly,or is maintained long enough for fluid in the semicircu-lar canals to stabilize, and the aircraft is quicklyreturned to straight and level, the motion of the fluid inthe canal will give the sensation that the aircraft isbanking in the opposite direction, and the pilot willhave a tendency to bank the aircraft into an attitudeerroneously perceived to be straight and Graveyard Spiral This is a high speed, tightdescending turn (not a spin, because the wing neverstalls) entered as a result of a failure to detect rollingmotion. Since any bank rate of less than two degreesper second is not felt, the wing may drop and the planemay begin a turn without the pilot realizing it.

10 As theplane spirals downward and its descent accelerates, thepilot senses the descent but not the turn. The naturaltendency is for the pilot to pull back on the yoke toarrest the altitude loss. But with the bank angle havinggradually increased, this control input only tightens theturn and increases the descent Illusion Abrupt movements of the headcan set the fluid in the semicircular canals moving in sucha way as to create an overwhelming sensation of tumblinghead over heels. The sensation can be so strong as to leadpilots to lose control of the aircraft. Looking down, as youmight when searching for a chart in the cockpit, and thenlooking up can cause vertigo. Inversion Illusion An abrupt change from climb tostraight-and-level flight can excessively stimulate thesensory organs for gravity and linear acceleration, creat-ing the illusion of tumbling Disorientation AccidentsThe Aeronautical Information Manual ranks Spatial Disorientation among the most cited contributing factors to fatal aircraft accidents.