Spatial Disorientation

Introduction:

  • Sensory mismatchs can result in a pilot's loss of orientation to the surrounding environment, also known as spatial disorientation
  • Disturbances to sensory systems or the inaccurate perception of a given situation may produce several dangerous illusions in flight
  • Driven by a variety of sources and interpretations, pilots can experience illusions in flight, which break down into four main categories: vestibular, visual, landing, and atmospheric
  • Vestibular system illusions consist of the inner ear's interpretation of orientation
  • Visual cues, supported by other senses, such as the vestibular system, are crucial metrics for maintaining spatial orientation
    • These cues are even more critical at night
  • Differences in runway size, width, and slope can also lead to illusions during landing
  • While many illusions are due to human limitations, atmospheric factors may also be at play
  • There are several steps pilots can take to prevent illusions from occurring; however, it is never possible to eliminate the risk
  • As such, pilots must be prepared to cope with spatial disorientation
  • Together, prevention and coping skills help mitigate dangerous outcomes from occurring
  • When you feel you have a solid understanding of taxiing, compare your knowledge against the Private Pilot (Airplane) and Commercial Pilot (Airplane) Spatial Disorientation Airman Certification Standards
  • Once satisfied, close out with the topic summary and prepare for your next lesson

WARNING:
All aeromedical topics are GENERALIZED.
Always consult with a doctor or physician to understand your specific situation

WARNING:
All procedures are GENERALIZED.
Fly the maneuver in accordance with the Pilot Operating Handbook (POH)
and/or current Standard Operating Procedures (SOPs)

Spatial Disorientation Overview:

  • Sensory Inputs
    Sensory Inputs
  • The three-dimensional environment of flight is unfamiliar to our bodies and creates sensory conflicts and illusions that make spatial orientation difficult
  • Generally, pilots determine the flight attitude of an airplane by reference to the natural horizon
  • When atmospheric or lighting conditions obscure the natural horizon, attitude can sometimes be maintained by reference to the surface below
  • If neither horizon nor surface references exist, the airplane's attitude is determined by artificial means - an attitude indicator or other flight instruments
  • However, during periods of low visibility, the supporting senses sometimes conflict with what is seen
  • When the sensory system doesn't agree with where you believe to be in space, spatial disorientation has occurred
  • Becoming spatially disoriented is the result of a properly functioning human system, which we are hard-wired to trust, misinterpreting our actual position or orientation in space
  • Sensory inputs can be broken into three categories:

  • Visual Sensory Input:

    • The eye gathers visual sensory inputs through visual acuity (focus), depth perception, and orientation
    • Visual cues are the largest contributor to determine spatial orientation
    • Conditions which preclude the eye's ability to sense (such as clouds, darkness, indistinct contrast between land and sky) will increase the chance of sensory mismatches and therefore spatial disorientation

  • Vestibular Sensory Input:

    • The vestibular system includes the sensory organs contained within the inner ear that detect relative motion of the head in space within its axes of movement
    • It consists of two major components:
      • Semicircular canals that detect changes in rotational acceleration
      • The otolith organs that detect linear (straight) acceleration
    • Accidents can occur due to a combination of vestibular illusions and poor visibility

  • Proprioceptive Sensory Input:

    • Proprioception is a term that encompasses the human sensation of the body's position
    • Proprioceptive sensory inputs give us a reference to posture and the relative position of our body in relation to our environment
  • Sensory Inputs
    Sensory Inputs

Illusions in Flight:

  • Vestibular System Illusions:

    • Vestibular system illusions are related to the inner ear
    • Inner-ear derived illusions include:

    • The Leans:

      • Instrument Flying Handbook. Figure 1-6, Angular Acceleration
        Instrument Flying Handbook, Angular Acceleration
      • If entering a turn too slowly to stimulate the motion sensing system in the inner ear (less than 2°/second), an abrupt correction of a banked attitude can create the illusion of banking in the opposite direction [Figure 1]
        • The body never detected the turn in the first place, still feeling as though the aircraft/pilot's body are straight and level
        • When rolling back to level, the body may detect this movement as rolling from level to the side, instead of back to level
        • If the pilot relies on what their body is telling them, the pilot might lean in the direction of the original turn to regain what you think is the correct vertical posture
      • The disoriented pilot will roll the aircraft back into its original attitude, or if level flight is maintained, will feel compelled to lean in the perceived vertical plane until this illusion subsides
      • Maintaining a good instrument scan allows the pilot to detect this sensory mismatch and maintain level despite what is felt
      • A breakdown in the instrument scan will lend to a pilot believing the body's sensation and not recognize the aircraft's attitude differs from expectations
      • Similarly, when a turn is entered slowly and if an instrument scan is poor, a pilot may never detect the sensation of a turn
        • The pilot may not recognize what is happening until the aircraft is in an aggressive unusual attitude
      • Instrument Flying Handbook. Figure 1-6, Angular Acceleration
        Instrument Flying Handbook, Angular Acceleration

    • Coriolis illusion:

      • The Coriolis illusion occurs when a pilot has been turning long enough for the fluid in the ear canal to move at the same speed as the canal, which is then followed by an abrupt head movement
      • A movement of the head in a different plane, such as looking at something in a different part of the flight deck or grabbing a chart, may set the fluid moving and create the illusion of turning or accelerating on an entirely different axis
      • The disoriented pilot may maneuver the aircraft into a dangerous attitude in an attempt to correct the aircraft's perceived attitude
      • Pilots must develop an instrument cross-check or scan that involves minimal head movement
      • Always avoid abrupt maneuvers with your head, especially at night or in instrument conditions, while making prolonged constant-rate turns

    • Graveyard Spin:

      • Proper recovery from spin stops stimulating the motion system
        • An abrupt stop can stimulate a spin in the opposite direction [Figure 2]
      • Pilot corrections for this illusion could return the aircraft into the original spin

    • Graveyard Spiral:

      • As in other illusions, a pilot in a prolonged coordinated, constant rate turn will eventually have the illusion of not turning [Figure 2]
      • An observed loss of altitude during a coordinated constant-rate turn that has ceased stimulating the motion sensing system can create the illusion of being in a descent with the wings level
      • During the recovery to level flight, the pilot will experience the sensation of turning in the opposite direction (leans)
      • The pilot may return the aircraft to its original turn and, in doing so, continue to lose altitude
      • Instruments will likely indicate a descent at this point, causing the pilot to try to correct for the illusion of a level descent
      • The pilot pulls back on the yoke, tightening the spiral and increasing the loss in altitude
      • Instrument Flying Handbook. Figure 1-7, Graveyard Spiral
        Instrument Flying Handbook, Graveyard Spiral

    • Somatogravic Illusion:

      • A rapid acceleration, like experienced during takeoff, stimulates the otolith organs in the same way as tilting the head backward
        • This action creates the illusion of having a nose-up attitude, especially in situations without good visual references
      • The disoriented pilot may push the aircraft into a nose-low or dive attitude
      • A rapid deceleration by quick reduction of the throttle(s) can have the opposite effect, with the disoriented pilot pulling the aircraft into a nose-up or stall attitude

    • Inversion Illusion:

      • An abrupt change from climb to straight and level will make the pilot feel like he is tumbling backward
      • The disoriented pilot will push the nose forward (low) and possibly intensify the illusion
      • It is as though you're in a recliner, and you feel like you are looking up and gravity is pushing you into the chair, but in reality, you're descending, and the aircraft accelerating downward is pushing you into the seat

    • Elevator Illusion:

      • An abrupt upward vertical acceleration, like when in an updraft, can stimulate the otolith organs to create the illusion of being in a climb
        • The disoriented pilot may push the aircraft into a nose-low attitude
      • An abrupt downward vertical acceleration, usually in a downdraft, has the opposite effect, with the disoriented pilot pulling the aircraft into a nose-up attitude

  • Visual/Night Illusions:

    • Of the senses, vision is the most important for safe flight
    • However, various terrain features and atmospheric conditions can create optical illusions
    • These illusions are primarily associated with landing
    • Since pilots must transition from reliance on instruments to visual cues outside the flight deck for landing at the end of an instrument approach, they must be aware of the potential problems associated with these illusions and take appropriate corrective action

    • False Horizon:

      • Dark nights tend to eliminate reference to a visual horizon
      • Sloping cloud formations, an obscured horizon, a dark scene spread with ground lights and stars, and specific geometric patterns of ground light can create the illusion of not being aligned with the horizon
      • Geometric patterns of ground light can create illusions of not being aligned correctly with the actual horizon
      • The disoriented pilot will align with an incorrect horizon and, hence, a dangerous attitude
      • As a result, pilots need to rely less on outside references at night and more on flight and navigation instruments

    • Autokinesis:

      • Caused by staring at a single point of light against a dark background for more than a few seconds
      • After a few moments, the light appears to move on its own
      • The disoriented pilot will lose control of the aircraft in attempting to align it with the light
      • To prevent this illusion, focus the eyes on objects at varying distances and avoid fixating on one target
      • Be sure to maintain a typical scan pattern

    • Vertigo:

      • A feeling of dizziness and disorientation caused by doubt in visual interpretation
      • Distractions and problems can result from a flickering light in the cockpit, anti-collision light, strobe lights, or other aircraft lights and can cause flicker vertigo
      • Often experienced from a lack of a well-defined horizon
      • Also experienced leaving a well-lit area (a runway) into darkness
      • Possible physical reactions include nausea, dizziness, grogginess, unconsciousness, headaches, or confusion

    • Black-hole Approach:

      • When landing at night from over water or non-lighted terrain, the runway lights are the only source of light
      • Without peripheral visual cues to help, pilots will have trouble orientating themselves relative to Earth (horizon)
      • The runway can seem out of position (down-sloping or up-sloping) and, in the worst case, results in landing short of the runway
      • Utilize visual glide-slope indicators, if available
      • If navigation aids (NAVAIDs) are unavailable, pilots should pay careful attention to using the flight instruments to assist in maintaining orientation and a normal approach
      • Night landings are further complicated by the difficulty of judging distance and the possibility of confusing approach and runway lights:
        • Bright runway and approach lighting systems, mainly where few lights illuminate the surrounding terrain, may create the illusion of less distance to the runway, leading to a higher-than-normal approach
        • When flying over terrain with only a few lights, it will make the runway recede or appear farther away, leading to a lower-than-normal approach
        • If the runway has a city in the distance on higher terrain, the tendency will be to fly a lower-than-normal approach
        • A good review of the airfield layout and boundaries before initiating any approach will help the pilot maintain a safe approach angle
          • For example, when a double row of approach lights joins the boundary lights of the runway, there can be confusion about where the approach lights terminate and runway lights begin
        • Under certain conditions, approach lights can make the aircraft seem higher in a turn to final than when its wings are level
      • The pilot should execute a go-around if at any time they are unsure of their position or altitude
      • While the black-hole illusion is typically thought of as a problem for approaches, it can also impact pilots on departures
      • See also: AOPA Air Safety Institute - Safety Quiz: IFR Into a Black Hole

  • Landing Illusions:

    • Various surface features and atmospheric conditions encountered in landing can create illusions of incorrect height above and distance from the runway threshold
    • Anticipating landing error illusions can prevent them during approaches, aerial visual inspection of unfamiliar airports before landing, using electronic glide slope or VASI systems when available, and maintaining optimum proficiency in landing procedures

    • Runway Width:

      [Figure 3]
      • Instrument Flying Handbook. Figure 1-9a, Runway Width Illusion
        Instrument Flying Handbook, Runway Width Illusion
      • A narrower-than-usual runway can create an illusion the aircraft is at a higher altitude than it actually is, especially when runway length-to-width relationships are comparable
        • The pilot who does not recognize this illusion will fly a lower approach, with the risk of striking objects along the approach path or landing short
      • A wider-than-usual runway can have the opposite effect, with the risk of leveling out high and landing hard or overshooting the runway
      • Instrument Flying Handbook. Figure 1-9a, Runway Width Illusion
        Instrument Flying Handbook, Runway Width Illusion

    • Runway Slope:

      [Figure 4]
      • Instrument Flying Handbook. Figure 1-9b, Runway Slope Illusion
        Instrument Flying Handbook, Runway Slope Illusion
      • An up-sloping runway, up-sloping terrain, or both can create an illusion the aircraft is at a higher altitude than it actually is
        • The pilot who does not recognize this illusion will fly a lower approach
      • Down-sloping runways and down-sloping approach terrain can cause pilots to fly higher approaches
        • Flying a higher approach can impact landing performance, eating into the runway available and devolving into higher approach speeds as pilots attempt to lose excess altitude
      • Instrument Flying Handbook. Figure 1-9b, Runway Slope Illusion
        Instrument Flying Handbook, Runway Slope Illusion

    • Featureless Terrain:

      • Lack of horizon or surface reference is common on an overwater flights, at night, or in low visibility conditions
      • An absence of surrounding ground features, such as overwater approach, darkened area, or terrain made featureless by snow, can create an illusion the aircraft is at a higher altitude than it is
      • This illusion is sometimes referred to as the "black hole approach" (explained above), causing pilots to fly a lower approach than is desired

    • Ground Lighting:

      • Light along a straight path, such as a road, can be mistaken for a runway
      • Bright runway and approach lighting systems, especially where few lights illuminate the surrounding terrain, may create the illusion of less distance to the runway, causing pilots to fly a higher approach
      • Conversely, the pilot overflying terrain, which has few lights to provide height cues, may make a lower-than-normal approach

    • Aircraft Lighting:

      • When the landing light illuminates the runway, just as with ground lighting illusions, it makes the lighted area appear higher than the non-lighted area
      • As a result, pilots may fly a higher-than-normal approach

  • Atmospheric Illusions:

    • Illusions concerning weather and the appearance it creates regarding terrain
    • Surface references or the natural horizon may at times become obscured by smoke, fog, smog, haze, dust, ice particles, or other phenomena, although visibility may be above Visual Flight Rule (VFR) minimums
      • This is especially true at airports located adjacent to large bodies of water or sparsely populated areas, where few, if any, surface references are available
    • Other contributors to disorientation are reflections from outside lights, sunlight shining through clouds, and light beams from the airplane's anti-collision rotating beacon

    • Water Refraction:

      • Rain on the windscreen can create an illusion of being at a higher altitude due to the horizon appearing lower than it is
        • This can result in flying a lower approach than is desired

    • Haze:

      • Haze can create an illusion of being farther from the runway
        • As a result, the pilot will tend to be low on the approach
      • Extremely clear air (clear, bright conditions of a high-altitude airport) can give the pilot the illusion of being closer to the runway
        • As a result, the pilot will tend to fly high on approach, which may result in an overshoot or go-around
      • The diffusion of light due to water particles on the windshield can adversely affect depth perception
      • The lights and terrain features normally used to gauge height during landing become less effective for the pilot

    • Fog:

      • Penetration of fog can create an illusion of pitching up
      • This may cause an abruptly steepened approach

Spatial Disorientation Prevention:

  1. Since it is not a matter of if, but when a pilot experience spatial disorientation, there are a few things pilots can do to prepare
  2. Fly often
  3. Avoid instrument meteorological conditions if you are not rated
  4. Practice partial panel instrument training (with a safety pilot) on a regular basis
  5. Various complex motions and forces and certain visual scenes encountered in flight can create illusions of motion and position
    • Spatial disorientation from these illusions can be prevented only by visual reference to reliable, fixed points on the ground or flight instruments
  6. Anticipate the possibility of visual illusions during approaches to unfamiliar airports, particularly at night or in adverse weather conditions
  7. Consult airport diagrams and the Chart Supplement U.S. for information on runway slope, terrain, and lighting
  8. Make frequent reference to the altimeter, especially during all approaches, day and night
  9. If possible, conduct aerial visual inspection of unfamiliar airports before landing
  10. Use Visual Approach Slope Indicator (VASI) or Precision Approach Path Indicator (PAPI) systems for a visual reference or an electronic glide slope whenever they are available
  11. Utilize the Visual Descent Point (VDP) found on many non-precision instrument approach procedure charts
  12. Recognize that the chances of being involved in an approach accident increase when some emergency or other activity distracts from usual procedures
  13. The following fundamental steps to assist in preventing spatial disorientation:
    1. Before flying with less than 3 miles visibility, obtain training and maintain proficiency in airplane control by reference to instruments
    2. When flying at night or in reduced visibility, use the flight instruments
    3. Maintain night currency if intending to fly at night. Include cross-country and local operations at different airports
    4. Study and become familiar with unique geographical conditions
    5. Check weather forecasts before departure, enroute, and at the destination. Be alert for weather deterioration
    6. Do not attempt visual flight when there is a possibility of getting trapped in deteriorating weather
    7. Rely on instrument indications unless the natural horizon or surface reference is clearly visible

Coping with Spatial Disorientation:

  • The sensations that lead to illusions during instrument flight conditions are everyday perceptions experienced by pilots
    • In fact, it is never a question of whether you will experience these illusions, but when
  • Pilots cannot wholly prevent undesirable sensations, but through training and awareness, pilots can ignore or suppress them by developing absolute reliance on the flight instruments
  • As pilots gain proficiency in instrument flying, they become less susceptible to these illusions and their effects
  • To prevent illusions and their potentially disastrous consequences, pilots must:
    1. Understand the causes of these illusions and remain always alert for them. Take the opportunity to understand and then experience spatial disorientation illusions in a device such as a Barany chair, a Vertigon, or a Virtual Reality Spatial Disorientation Demonstrator
    2. Always obtain and understand preflight weather briefings
    3. Before flying in marginal visibility (less than 3 miles) or where a visible horizon is not evident, such as flight over open water during the night, obtain training and maintain proficiency in airplane control by reference to instruments
    4. Only continue flight into adverse weather conditions or dusk or darkness if proficient in using flight instruments. If intending to fly at night, maintain night-flight currency and proficiency. Include cross-country and local operations at various airfields
    5. Ensure that when using outside visual references, they are reliable, fixed points on the Earth's surface
    6. Avoid sudden head movement, particularly during takeoffs, turns, and approaches to landing
    7. Be physically tuned for flight into reduced visibility by following the "IMSAFE" checklist. That is, ensure proper rest and adequate diet, and allow for night adaptation if flying at night. Remember that illness, medication, alcohol, fatigue, sleep loss, and mild hypoxia are likely to increase susceptibility to spatial disorientation
    8. Most importantly, become proficient in using flight instruments and rely upon them. Trust the instruments and disregard your sensory perceptions

Spatial Disorientation Risk Factors:

  • Age, fatigue, stress, anxiety, certain medical conditions, medications, smoking, alcohol, and other drugs that affect the visual, vestibular, or proprioceptive sensory inputs can also increase susceptibility
  • When visual cues are absent, your body will turn to your vestibular system for information
  • The vestibular system is complex and can be easily deceived in certain flight conditions
    • When motion makes this system unreliable, pilots experience vestibular illusions. These dangerous illusions are the most likely culprits of spatial disorientation

Spatial Disorientation Demonstration:

  • A spatial disorientation demonstration enhances flight training by exposing student pilots to various sensations they could encounter in flight as well as the attitudes that could trigger those sensations

  • Spatial Disorientation Demonstration Purpose:

    1. There are a number of controlled aircraft maneuvers a pilot can perform to experiment with spatial disorientation
    2. While each maneuver will normally create a specific illusion, any false sensation is an effective demonstration of disorientation
    3. Thus, even if there is no sensation during any of these maneuvers, the absence of sensation is still an effective demonstration in that it shows the inability to detect bank or roll
    4. There are several objectives in demonstrating these various maneuvers
    5. A pilot should not attempt any of these maneuvers at low altitudes, or in the absence of an instructor pilot or an appropriate safety pilot

    6. In the descriptions of these maneuvers, the instructor pilot is doing the flying, but having the pilot do the flying can also be a very effective demonstration
    7. The pilot should close his or her eyes and tilt the head to one side
    8. The instructor pilot tells the pilot what control inputs to perform
    9. The pilot then attempts to establish the correct attitude or control input with eyes closed and head tilted
    10. While it is clear the pilot has no idea of the actual attitude, he or she will react to what the senses are saying
    11. After a short time, the pilot will become disoriented and the instructor pilot then tells the pilot to look up and recover
    12. The benefit of this exercise is the pilot experiences the disorientation while flying the aircraft
    13. They teach pilots to understand the susceptibility of the human system to spatial disorientation
    14. They demonstrate that judgments of aircraft attitude based on bodily sensations are frequently false
    15. They help lessen the occurrence and degree of disorientation through a better understanding of the relationship between aircraft motion, head movements, and resulting disorientation
    16. They help instill a greater confidence in relying on flight instruments for assessing true aircraft attitude

  • Spatial Disorientation Demonstration Procedure:

    1. Climbing While Accelerating:

      • With the pilot not flying's eyes closed, the instructor pilot maintains approach airspeed in a straight-and-level attitude for several seconds, and then accelerates while maintaining straight-and-level attitude
      • The usual illusion during this maneuver, without visual references, will be that the aircraft is climbing

    2. Climbing While Turning:

      • With the pilot's eyes still closed and the aircraft in a straight-and-level attitude, the instructor pilot now executes, with a relatively slow entry, a well-coordinated turn of about 1.5 positive G (approximately 50° bank) for 90°
      • While in the turn, without outside visual references and under the effect of the slight positive G, the usual illusion produced is that of a climb
      • Upon sensing the climb, the pilot should immediately open the eyes and see that a slowly established, coordinated turn produces the same feeling as a climb

    3. Diving While Turning:

      • Repeating the previous procedure, with the exception that the pilot's eyes should be kept closed until recovery from the turn is approximately one-half completed can create this sensation
      • With the eyes closed, the usual illusion will be that the aircraft is diving

    4. Tilting to Right or Left:

      • While in a straight-and-level attitude, with the pilot's eyes closed, the instructor pilot executes a moderate or slight skid to the left with wings level
      • This creates the illusion of the body being tilted to the right

    5. Reversal of Motion:

      • This illusion can be demonstrated in any of the three planes of motion. While straight and level, with the pilot's eyes closed, the instructor pilot smoothly and positively rolls the aircraft to approximately a 45° bank attitude while maintaining heading and pitch attitude
      • This creates the illusion of a strong sense of rotation in the opposite direction
      • After this illusion is noted, the pilot should open his or her eyes and observe that the aircraft is in a banked attitude

    6. Diving or Rolling Beyond the Vertical Plane:

      • This maneuver may produce extreme disorientation
      • While in straight-and-level flight, the pilot should sit normally, either with eyes closed or gaze lowered to the floor
      • The instructor pilot starts a positive, coordinated roll toward a 30° or 40° angle of bank
      • As this is in progress, the pilot tilts his or her head forward, looks to the right or left, then immediately returns his or her head to an upright position
      • The instructor pilot should time the maneuver so the roll is stopped as the pilot returns his or her head upright
      • An intense disorientation is usually produced by this maneuver, and the pilot experiences the sensation of falling downward into the direction of the roll

Spatial Disorientation Case Studies:

  • NTSB Identification: WPR11FA256 The National Transportation Safety Board determines the probable cause(s) of this accident to be: the non-instrument-rated pilot's decision to conduct a visual flight rules flight over mountainous terrain into a region covered by clouds, which likely resulted in spatial disorientation and subsequent loss of airplane control
  • NTSB Identification: CEN13FA135 The National Transportation Safety Board determines the probable cause(s) of this accident to be: The pilot's inadvertent controlled descent into terrain due to spatial disorientation. Contributing to the accident was a lack of visual reference due to night conditions

Conclusion:

  • Between 5 to 10% of all general aviation accidents are attributed to spatial disorientation, and 90% of those are fatal
    • NTSB data suggests that spatial D is a more common occurrence at night or in limited visibility weather conditions
  • Illusions rank among the most common factors cited as contributing to fatal aircraft accidents
  • The degree of disorientation may vary considerably with individual pilots, as do the conditions that induce the problem
  • Various complex motions and forces and certain visual scenes encountered in flight can create illusions of motion and position
  • Spatial disorientation from these illusions can be prevented only by visual reference to reliable, fixed points on the ground or flight instruments
  • The acronym "ICEFLAGS" is a tool to remember the different types of vestibular and visual/night illusions
    • Inversion, Coriolis, Elevator, False horizon, Leans, Autokinesis, Graveyard Spiral, Somatogravic
  • Review your illusions in flight knowledge by taking the Air Safety Institute's "Into a Black Hole" quiz
  • Consider completing the AOPA's spatial orientation spotlight to learn more about spatial disorientation
  • Consider practicing maneuvers on a flight simulator to introduce yourself to maneuvers or knock off rust
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References: