Spatial Disorientation & Illusions In Flight

Vestibular System Illusions:

• Vestibular system illusions are related to the inner ear.
• Vestibular (inner-ear) illusions include:
  • The Leans.
  • Coriolis Illusion.
  • Graveyard Spin.
  • Graveyard Spiral.
  • Somatogravic Illusion.
  • Inversion Illusion.
  • Elevator Illusion.

• The Leans:

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  • 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. []
    • Because the initial turn went undetected, the pilot still feels as though the aircraft is straight and level.
    • When the aircraft returns to level flight, the pilot may feel a bank in the opposite direction.
    • A pilot relying on bodily sensations may lean in the direction of the original turn to regain what feels like an upright posture.
  • The disoriented pilot may roll back into the original bank or, while maintaining level flight, feel compelled to lean until the illusion subsides.
  • Maintaining an effective instrument scan helps the pilot detect this sensory mismatch and maintain level flight.
  • A breakdown in the instrument scan can cause a pilot to trust bodily sensations and overlook a difference between the aircraft's actual and perceived attitude.
  • Similarly, when entering a turn 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.

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• Coriolis Illusion:

  • The Coriolis illusion can occur when an abrupt head movement follows a prolonged turn, after the fluid in the semicircular canals has begun moving with the canals.
  • Moving the head in a different plane—for example, looking elsewhere in the flight deck or reaching for a chart—may set the inner-ear fluid moving and create the illusion of turning or accelerating about a different axis.
  • A disoriented pilot attempting to correct the aircraft's perceived attitude may inadvertently maneuver into a dangerous attitude.
  • Pilots must develop an instrument cross-check or scan that minimizes head movement.
  • Avoid abrupt head movements during prolonged, constant-rate turns, especially at night or in instrument conditions.

• Graveyard Spin:

  • During a prolonged spin, the pilot's motion-sensing system may stop detecting the rotation.
    • Stopping the spin can create the illusion of spinning in the opposite direction. []
  • A pilot attempting to counteract this false sensation may reenter the original spin.

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• Graveyard Spiral:

  • During a prolonged, coordinated, constant-rate turn, a pilot may feel as though the aircraft is no longer turning. []
  • If the pilot no longer senses a coordinated, constant-rate turn, an observed altitude loss can create the illusion of descending with the wings level.
  • When recovering to level flight, the pilot may feel a turn in the opposite direction.
  • The disoriented pilot may resume the original turn, allowing the aircraft to continue descending.
  • Seeing the instruments indicate a descent, the pilot may attempt to stop the altitude loss while mistakenly believing the wings are level.
  • Pulling back on the yoke tightens the spiral and increases the rate of descent.

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• Somatogravic Illusion:

  • Rapid acceleration, such as during takeoff, stimulates the otolith organs similarly to tilting the head backward.
    • This acceleration can create the illusion of a nose-up attitude, especially when clear visual references are absent.
  • Reacting to this illusion, the pilot may lower the nose into a dive.
  • Rapid deceleration, such as after a quick throttle reduction, can produce the opposite illusion, prompting the pilot to raise the nose and potentially stall the aircraft.

• Inversion Illusion:

  • An abrupt transition from a climb to straight-and-level flight can create the sensation of tumbling backward.
  • The disoriented pilot may lower the aircraft's nose, potentially intensifying the illusion.
  • It is as though you're in a recliner, and you feel as though you're looking up, but gravity is actually pulling you into the chair. In reality, you're descending, and the aircraft's acceleration downward is pushing you into the seat.

• Elevator Illusion:

  • An abrupt upward acceleration, such as in a brief updraft, can stimulate the otolith organs and create the illusion of being in a climb.
    • The disoriented pilot may push the aircraft into a nose-low attitude.
  • An abrupt downward acceleration, such as in a brief downdraft, can have the opposite effect, prompting the disoriented pilot to raise the aircraft's nose.

Visual/Night Illusions:

• Of the senses, vision is the most important for safe flight.
• Terrain features and atmospheric conditions can create optical illusions.
• These illusions are primarily associated with landing.
• When transitioning from instruments to outside visual cues for landing after an instrument approach, pilots must recognize potential visual illusions and take appropriate corrective action.

• False Horizon:

  • On dark nights, the natural horizon may be difficult or impossible to see.
  • Sloping cloud formations, an obscured horizon, ground lights mixed with stars, and geometric patterns of ground lights can create a false horizon, misleading pilots about the aircraft's attitude.
  • A disoriented pilot may align the aircraft with a false horizon, placing it in a dangerous attitude.
  • At night, pilots should cross-check outside visual references with flight and navigation instruments.

• Autokinesis:

  • Autokinesis can occur after staring at a single point of light against a dark background for more than a few seconds.
  • After a few moments, the stationary light may appear to move.
  • A disoriented pilot attempting to align the aircraft with the apparently moving light may lose control of the aircraft.
  • To help prevent this illusion, shift your focus among objects at different distances and avoid fixating on a single target.
  • Maintain a regular scan pattern.

• Vertigo:

  • A feeling of dizziness and disorientation caused by doubt in visual interpretation.
  • Flickering cockpit lights, anti-collision lights, strobes, or other aircraft lights can cause flicker vertigo.
  • Vertigo is often experienced when there is no well-defined horizon.
  • Vertigo can also occur when transitioning from a well-lit area, such as a runway, into darkness.
  • Possible symptoms include nausea, dizziness, grogginess, loss of consciousness, headaches, or confusion.

• Black-Hole Approach:

  • During a night approach over water or unlit terrain, runway lights may be the only visible lights.
  • A lack of peripheral visual cues can make it difficult for pilots to orient themselves relative to the horizon.
  • The runway may appear to slope upward or downward, and misjudging the approach can lead to landing short of the runway.
  • Use visual glide-slope indicators, if available.
  • If navigation aids (NAVAIDs) are unavailable, pilots should use flight instruments to maintain orientation and follow a standard approach profile.
  • Difficulty judging distance and distinguishing approach lights from runway lights can further complicate night landings:
    • Bright runway and approach lights, particularly in otherwise dark areas, may make the runway appear closer, leading to a higher-than-normal approach angle.
    • Over sparsely lit terrain, the runway may appear farther away, leading to a lower-than-normal approach.
    • If the runway is near a city on higher terrain in the distance, pilots may fly a lower-than-normal approach.
    • Reviewing the airfield layout and boundaries before an approach can help the pilot maintain a safe approach angle.
      • Where a double row of approach lights meets the runway boundary lights, pilots may have difficulty identifying where the approach lights end and the runway lights begin.
    • Under certain conditions, approach lights can make the aircraft appear higher during the turn to final than when its wings are level.
  • If unsure of their position or altitude during the approach, the pilot should go around.
  • The black-hole illusion can also affect departures.
  • See also: AOPA Air Safety Institute - Safety Quiz: IFR Into a Black Hole.

Landing Illusions:

• Surface features and atmospheric conditions during landing can distort a pilot's perception of height above and distance from the runway threshold.
• To reduce landing errors caused by illusions, anticipate misleading visual cues, visually inspect unfamiliar airports from the air before landing, use available glide slope or Visual Approach Slope Indicator (VASI) guidance, and maintain proficiency in landing procedures.

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• Runway Width:

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  • A narrower-than-usual runway can create an illusion in which the aircraft appears to be at a higher altitude than it actually is, especially when the runway's length-to-width ratio is comparable.
    • A pilot who does not recognize this illusion may fly a lower approach, increasing the risk of striking obstacles or landing short of the intended touchdown point.
  • A wider-than-usual runway can have the opposite effect, increasing the risk of leveling off too high, landing hard, or overshooting the runway.

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• Runway Slope:

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  • An up-sloping runway, up-sloping terrain, or both can make the aircraft appear higher than it actually is.
    • A pilot who does not recognize this illusion may fly a lower-than-normal approach.
  • Down-sloping runways and approach terrain can lead pilots to fly higher-than-normal approaches.
    • A higher-than-normal approach can affect landing performance by leaving less runway for the landing roll and increasing airspeed as the pilot attempts to lose excess altitude.

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• Featureless Terrain:

  • Horizon or surface references may be unavailable during overwater flights, at night, or in low visibility.
  • A lack of visible ground features during approaches over water, dark areas, or snow-covered terrain can make the aircraft appear higher than it actually is.
  • This illusion, sometimes called the “black-hole approach” (explained above), can lead pilots to fly a lower-than-normal approach.

• Ground Lighting:

  • A line of lights, such as those along a road, can be mistaken for a runway.
  • Bright runway and approach lights, especially against dark surrounding terrain, can make the runway appear closer than it is, prompting a higher-than-normal approach.
  • Conversely, flying over terrain with few lights to provide height cues may lead to a lower-than-normal approach.

• Aircraft Lighting:

  • Landing-light illumination can make the illuminated area appear higher than the surrounding unlit area, potentially leading pilots to fly a higher-than-normal approach.

Atmospheric Illusions:

• Atmospheric conditions can distort the appearance of terrain, creating visual illusions.
• Smoke, fog, smog, haze, dust, ice particles, or other phenomena can obscure surface references or the natural horizon.
  • This can occur even when visibility exceeds Visual Flight Rules (VFR) minimums.
  • Obscuration is more likely at airports located adjacent to large bodies of water or sparsely populated areas, where few, if any, surface references are available.
• Reflections from outside lights, sunlight shining through clouds, and beams from the aircraft's rotating anti-collision beacon can also contribute to disorientation.

• Water Refraction:

  • Rain on the windscreen can make the horizon appear lower, creating the illusion that the aircraft is higher than it actually is.
    • Pilots experiencing this illusion may fly a lower-than-intended approach.

• Haze:

  • Haze can make the runway appear farther away than it actually is.
    • This illusion may lead the pilot to fly a lower-than-normal approach.
  • Clear, bright conditions, such as those at a high-altitude airport, can make the runway appear closer than it actually is.
    • This illusion may lead to a higher-than-normal approach, potentially resulting in an overshoot or a go-around.
  • Water droplets on the windscreen can scatter light and impair depth perception.
  • These conditions make lights and terrain features less reliable for judging height during landing.

• Fog:

  • Entering fog can create the illusion that the aircraft is pitching up.
  • Pilots reacting to this illusion may abruptly steepen their approach.

Spatial Disorientation Demonstration Purpose:

1. Controlled aircraft maneuvers can help pilots experience and understand spatial disorientation.
2. Although each maneuver typically produces a specific illusion, any false sensation can demonstrate disorientation.
3. Even when a maneuver produces no sensation, it demonstrates that bodily senses may fail to detect bank or roll.
4. Do not attempt these maneuvers at low altitudes or without an instructor or appropriate safety pilot.
5. The instructor typically flies these demonstrations, but having the pilot fly under the instructor's direction can also demonstrate disorientation effectively.
   • The pilot should close their eyes and tilt their head to one side.
   • The instructor directs the pilot's control inputs.
   • With eyes closed and head tilted, the pilot attempts to establish the requested attitude or make the instructed control input.
   • Without visual references, the pilot may react to bodily sensations without knowing the aircraft's actual attitude.
   • After a short time, the pilot will become disoriented, and the instructor pilot then tells the pilot to look up and recover.
   • This exercise allows the pilot to experience disorientation while controlling the aircraft.
6. Spatial disorientation objectives:
   • These demonstrations help pilots understand human susceptibility to spatial disorientation.
   • These demonstrations show that bodily sensations can give a false impression of aircraft attitude.
   • These demonstrations help pilots understand how aircraft motion and head movements contribute to disorientation, helping reduce its occurrence and severity.
   • These demonstrations build confidence in using flight instruments to determine aircraft attitude.

Spatial Disorientation Demonstration Procedure:

1. Climbing While Accelerating:

   • With the pilot's eyes closed, the instructor maintains approach airspeed in a straight-and-level attitude for several seconds, then accelerates while maintaining the same attitude.
   • Without visual references, the pilot may feel as though the aircraft is climbing during this maneuver.

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°.
   • Without outside visual references, the slight positive G during the turn can create the sensation of climbing.
   • Upon sensing a climb, the pilot should immediately open their eyes to observe that a gradually established, coordinated turn can feel like a climb.

3. Diving While Turning:

   • Repeating the previous procedure with eyes closed until about halfway through recovery from the turn can create a sensation of diving.

4. Tilting to the Right or Left:

   • With the aircraft straight and level and the pilot's eyes closed, the instructor introduces a slight or moderate skid to either side while keeping the wings level.
   • This maneuver creates the illusion of the body tilting opposite the direction of the skid.

5. Reversal of Motion:

   • The reversal of motion illusion can be demonstrated in any of the three planes of motion.
   • While the aircraft is straight and level, with the pilot's eyes closed, the instructor pilot smoothly and positively rolls the aircraft to approximately a 45° bank angle, maintaining its heading and pitch attitude.
   • The reversal of motion illusion creates a strong sensation of rotating opposite the aircraft's actual roll direction.
   • After experiencing this illusion, the pilot should open their eyes and observe the aircraft's actual banked attitude.

6. Diving or Rolling Beyond the Vertical Plane:

   • This maneuver may produce extreme disorientation.
   • During straight-and-level flight, the pilot should sit normally with eyes closed or gaze directed toward the floor.
   • The instructor initiates a positive, coordinated roll toward a 30° or 40° bank angle.
   • During the roll, the pilot tilts their head forward, looks right or left, and then immediately returns their head upright.
   • The instructor should time the maneuver so that the roll stops as the pilot returns their head upright.
   • This maneuver can produce intense disorientation and a sensation of falling in the direction of the roll.