Human senses
A sense is a biological system used by an organism for sensation, the process of gathering information about the world through the detection of stimuli. (For example, in the human body, the brain which is part of the central nervous system rec ...
are not naturally geared for the inflight environment. Pilots may experience disorientation and loss of perspective, creating illusions that range from false horizons to sensory conflict with instrument readings or the misjudging of altitude over water.
Vestibular system
The
vestibular system
The vestibular system, in vertebrates, is a sensory system that creates the sense of balance and spatial orientation for the purpose of coordinating movement with balance. Together with the cochlea, a part of the auditory system, it constitutes ...
, which is responsible for the sense of balance in humans, consists of the
otolith
An otolith ( grc-gre, ὠτο-, ' ear + , ', a stone), also called statoconium or otoconium or statolith, is a calcium carbonate structure in the saccule or utricle of the inner ear, specifically in the vestibular system of vertebrates. The sa ...
organs and the
semicircular canals
The semicircular canals or semicircular ducts are three semicircular, interconnected tubes located in the innermost part of each ear, the inner ear. The three canals are the horizontal, superior and posterior semicircular canals.
Structure
The ...
. Illusions in aviation are caused when the brain cannot reconcile inputs from the vestibular system and
visual system
The visual system comprises the sensory organ (the eye) and parts of the central nervous system (the retina containing photoreceptor cells, the optic nerve, the optic tract and the visual cortex) which gives organisms the sense of sight (the a ...
. The three semicircular canals, which recognize accelerations in
pitch,
yaw, and
roll
Roll or Rolls may refer to:
Movement about the longitudinal axis
* Roll angle (or roll rotation), one of the 3 angular degrees of freedom of any stiff body (for example a vehicle), describing motion about the longitudinal axis
** Roll (aviation), ...
, are stimulated by
angular acceleration
In physics, angular acceleration refers to the time rate of change of angular velocity. As there are two types of angular velocity, namely spin angular velocity and orbital angular velocity, there are naturally also two types of angular acceler ...
s; while the otolith organs, the
saccule
The saccule is a bed of sensory cells in the inner ear. It translates head movements into neural impulses for the brain to interpret. The saccule detects linear accelerations and head tilts in the vertical plane. When the head moves verticall ...
and
utricle, are stimulated by linear accelerations. Stimulation of the semicircular canals occurs when the movement of the
endolymph
Endolymph is the fluid contained in the membranous labyrinth of the inner ear. The major cation in endolymph is potassium, with the values of sodium and potassium concentration in the endolymph being 0.91 mM and 154 mM, respectively. I ...
inside the canals causes movement of the
crista ampullaris
The crista ampullaris is the sensory organ of rotation. They are found in the osseous ampullae, ampullae of each of the semicircular canals of the inner ear, meaning that there are three pairs in total. The function of the crista ampullaris is to ...
and the hair cells within them. Stimulation of the otolith organs occurs when
gravitational forces or linear accelerations cause movement of the otolith membrane, the otoliths, or the hair cells of the
macula
The macula (/ˈmakjʊlə/) or macula lutea is an oval-shaped pigmented area in the center of the retina of the human eye and in other animals. The macula in humans has a diameter of around and is subdivided into the umbo, foveola, foveal avas ...
.
Somatogyral illusions occur as a result of angular accelerations stimulating the semicircular canals. Somatogravic illusions, on the other hand, occur as a result of linear accelerations stimulating the otolith organs.
Vestibular/somatogyral
Illusions involving the
semicircular
In mathematics (and more specifically geometry), a semicircle is a one-dimensional locus of points that forms half of a circle. The full arc of a semicircle always measures 180° (equivalently, radians, or a half-turn). It has only one line of ...
and
somatogyral canals of the
vestibular system
The vestibular system, in vertebrates, is a sensory system that creates the sense of balance and spatial orientation for the purpose of coordinating movement with balance. Together with the cochlea, a part of the auditory system, it constitutes ...
of the ear occur primarily under conditions of unreliable or unavailable external visual references and result in false sensations of rotation. These include
the leans
The leans is the most common type of spatial disorientation for aviators. Through stabilization of the fluid in the semicircular canals, a pilot may perceive straight and level flight while actually in a banked turn. This is caused by a quick retu ...
, the graveyard spin and
spiral
In mathematics, a spiral is a curve which emanates from a point, moving farther away as it revolves around the point.
Helices
Two major definitions of "spiral" in the American Heritage Dictionary are:[Coriolis illusion
In psychophysical perception, the Coriolis effect (also referred to as the Coriolis illusion) is the misperception of body orientation and induced nausea due to the Coriolis force. This effect comes about as the head is moved in contrary or simi ...]
.
The leans
This is the most common illusion during flight, and can be caused by a sudden return to wings-level flight following a gradual entry and prolonged application of
bank
A bank is a financial institution that accepts deposits from the public and creates a demand deposit while simultaneously making loans. Lending activities can be directly performed by the bank or indirectly through capital markets.
Because ...
that had gone unnoticed by the pilot.
[ The reason a pilot can be unaware of such an attitude change in the first place is that human exposure to a rotational acceleration of ~1 degrees per second² or lower is below the detection threshold of the ]semicircular canals
The semicircular canals or semicircular ducts are three semicircular, interconnected tubes located in the innermost part of each ear, the inner ear. The three canals are the horizontal, superior and posterior semicircular canals.
Structure
The ...
. Rolling wings-level from such an attitude may cause an illusion that the aircraft is banking in the opposite direction. In response to such an illusion, a pilot will tend to roll back in the direction of the original bank in a corrective attempt to regain the perception of a level attitude
Attitude may refer to:
Philosophy and psychology
* Attitude (psychology), an individual's predisposed state of mind regarding a value
* Metaphysics of presence
* Propositional attitude, a relational mental state connecting a person to a pro ...
.
Graveyard spin
The graveyard spin is an illusion that can occur to a pilot who enters into a spin
Spin or spinning most often refers to:
* Spinning (textiles), the creation of yarn or thread by twisting fibers together, traditionally by hand spinning
* Spin, the rotation of an object around a central axis
* Spin (propaganda), an intentionally b ...
and is characterized by the pilot becoming less aware of the sense of rotation induced by the spin as the spin continues. As the pilot becomes less aware of the spin, any correction of the spin may cause the pilot to sense that he or she is spinning in the opposite direction. As an example, if the airplane is spinning to the right but goes unnoticed for a period of time sufficient for the pilot to become desensitized to the magnitude of the spin, a small adjustment to the left rudder
A rudder is a primary control surface used to steer a ship, boat, submarine, hovercraft, aircraft, or other vehicle that moves through a fluid medium (generally aircraft, air or watercraft, water). On an aircraft the rudder is used primarily to ...
may leave the pilot with a sensation of spinning to the left. As a result, the pilot will apply right rudder and unknowingly re-enter the original right spin. Cross-checking the airplane's flight instruments
Flight instruments are the instruments in the cockpit of an aircraft that provide the pilot with data about the flight situation of that aircraft, such as altitude, airspeed, vertical speed, heading and much more other crucial information in fli ...
would show that the airplane is still in a turn, which causes sensory conflict for the pilot. If the pilot does not correct the spin, the airplane will continue to lose altitude until contact with the terrain occurs.
Graveyard spiral
The graveyard spiral is characterized by the pilot mistakenly believing he or she is in wings-level flight when the aircraft is in fact engaged in a banking turn, and notices the altimeter
An altimeter or an altitude meter is an instrument used to measure the altitude of an object above a fixed level. The measurement of altitude is called altimetry, which is related to the term bathymetry, the measurement of depth under water. The m ...
indicating an ongoing drop in altitude. The sensory disorientation of returning from a prolonged banking turn to wings-level flight can cause the pilot to re-enter the banking turn, as in the graveyard spin illusion. While the plane continues in the turn and begins to indicate a loss of altitude, the pilot will try to correct the loss of altitude by "pulling up" on the plane's controls.[ Attempting to adjust the controls in this way will have the effect of tightening the ]radius
In classical geometry, a radius ( : radii) of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length. The name comes from the latin ''radius'', meaning ray but also the ...
of the turn and eventually quickening the rate of descent until the pilot is visually cued to the nature of the error or contact with the terrain occurs. Two of the most famous cases of an aircraft mishap from this form of spatial disorientation was the 1963 crash that killed singer Patsy Cline near Camden, Tennessee
Camden is a city in Benton County, Tennessee, United States. The population was 3,674 at the 2020 census. It is the county seat of Benton County.
History
Native Americans were living in the Camden area as early as the Archaic period (8000-1000 B ...
and also the 1999 crash that killed John F. Kennedy Jr. near Martha's Vineyard
Martha's Vineyard, often simply called the Vineyard, is an island in the Northeastern United States, located south of Cape Cod in Dukes County, Massachusetts, known for being a popular, affluent summer colony. Martha's Vineyard includes the s ...
.
Coriolis illusion
This involves the simultaneous stimulation of two semicircular canals and is associated with a sudden tilting (forward or backwards) of the pilot's head while the aircraft is turning. This can occur when tilting the head down (to look at an approach chart or to write on the knee pad), up (to look at an overhead instrument or switch), or sideways. This can produce an overpowering sensation that the aircraft is rolling, pitching, and yawing all at the same time, which can be compared with the sensation of rolling down a hillside. This illusion can make the pilot quickly become disoriented and lose control of the aircraft.[
]
Vestibular/somatogravic
Somatogravic illusions are caused by linear accelerations. These illusions involving the utricle and the saccule
The saccule is a bed of sensory cells in the inner ear. It translates head movements into neural impulses for the brain to interpret. The saccule detects linear accelerations and head tilts in the vertical plane. When the head moves verticall ...
of the vestibular system
The vestibular system, in vertebrates, is a sensory system that creates the sense of balance and spatial orientation for the purpose of coordinating movement with balance. Together with the cochlea, a part of the auditory system, it constitutes ...
are most likely to occur under conditions with unreliable or unavailable external visual references.
Inversion
An abrupt change from climb to straight-and-level flight can stimulate the otolith organs enough to create the illusion of tumbling backwards, or inversion illusion. The disoriented pilot may push the aircraft abruptly into a nose-low attitude, possibly intensifying this illusion.[
]
Head-up
The head-up illusion involves a sudden forward linear acceleration during level flight where the pilot perceives the illusion that the nose of the aircraft is pitching up. The pilot's response to this illusion would be to push the yoke
A yoke is a wooden beam sometimes used between a pair of oxen or other animals to enable them to pull together on a load when working in pairs, as oxen usually do; some yokes are fitted to individual animals. There are several types of yoke, us ...
or the stick
Stick or the stick may refer to:
Thin elongated objects
* Twig
* The weapon used in stick fighting
* Walking stick, a device to facilitate balancing while walking
* Shepherd's crook
* Swagger stick
* Digging stick
* Swizzle stick, used to stir d ...
forward to pitch the nose of the aircraft down. A night take-off from a well-lit airport into a totally dark sky (black hole
A black hole is a region of spacetime where gravitation, gravity is so strong that nothing, including light or other Electromagnetic radiation, electromagnetic waves, has enough energy to escape it. The theory of general relativity predicts t ...
) or a catapult
A catapult is a ballistic device used to launch a projectile a great distance without the aid of gunpowder or other propellants – particularly various types of ancient and medieval siege engines. A catapult uses the sudden release of stored p ...
take-off from an aircraft carrier
An aircraft carrier is a warship that serves as a seagoing airbase, equipped with a full-length flight deck and facilities for carrying, arming, deploying, and recovering aircraft. Typically, it is the capital ship of a fleet, as it allows a ...
can also lead to this illusion, and could result in a crash.[
]
Head-down
The head-down illusion involves a sudden linear deceleration ( air braking, lowering flaps, decreasing engine power) during level flight where the pilot perceives the illusion that the nose of the aircraft is pitching down. The pilot's response to this illusion would be to pitch the nose of the aircraft up. If this illusion occurs during a low-speed final approach, the pilot could stall the aircraft.[
]
Visual
Visual illusions are familiar to most of us. Even under conditions of good visibility, one can experience visual illusions.
Linear perspective
This illusion may make a pilot change (increase or decrease) the slope of their final approach. They are caused by runways with different widths, upsloping or downsloping runways, and upsloping or downsloping final approach terrain. Pilots learn to recognize a normal final approach by developing and recalling a mental image of the expected relationship between the length and the width of an average runway. An example would be a pilot used to small general aviation fields visiting a large international airport. The much wider runway would give the pilot the mental picture of the point where they would usually begin the flare, when they are much higher than they should be. A pilot flying an aircraft where the cockpit height relative to the ground is vastly higher or lower than they are used to can cause a similar illusion in the last part of the approach.
Upsloping terrain or narrow or long runway
A final approach over an upsloping terrain with a flat runway, or to an unusually narrow or long runway may produce the visual illusion of being too high on final approach. The pilot may then increase their rate of descent, positioning the aircraft unusually low on the approach path.[
]
Downsloping terrain or wide runway
A final approach over a downsloping terrain with a flat runway, or to an unusually wide runway may produce the visual illusion of being too low on final approach. The pilot may then pitch the aircraft's nose up to increase the altitude, which can result in a low-altitude stall or a missed approach.[
]
Other
Black-hole approach
A black-hole approach illusion can happen during a final approach at night (with no stars or moonlight) over water or unlit terrain to a lighted runway, in which the horizon is not visible.[ As the name suggests, it involves an approach to landing during the night where there is nothing to see between the aircraft and the intended runway, there is just a visual “black-hole”. Pilots too often confidently proceed with a visual approach instead of relying on instruments during nighttime landings. As a result, this can lead to the pilot experiencing glide path overestimation (GPO) because of the lack of peripheral visual cues, especially, below the aircraft. In addition, with no peripheral visual cues allowing for an orientation relative to the earth there can be an illusion of the pilot being upright and the runway being tilted and sloping. As a result, they initiate an aggressive descent and wrongly adjust to an unsafe glide path below the desired three-degree glide path.][
]
Autokinesis
The autokinetic illusion occurs at night or in conditions with poor visual cues. This illusion gives the pilot the impression that a stationary object is moving in front of the airplane's path; it is caused by staring at a fixed single point of light (ground light or a star) in a totally dark and featureless background. The reason why this visual illusion occurs is because of very small movements of the eyes. In conditions with poor visual cues accompanied by a single source of light, these eye movements are interpreted by the brain as movement of the object being viewed.[ This illusion can cause a misperception that such a light is on a collision course with the aircraft.][
Planets or stars in the night sky can often cause the illusion to occur. Often these bright stars or planets have been mistaken for landing lights of oncoming aircraft, satellites, or even UFOs. An example of a star that commonly causes this illusion is Sirius, which is the brightest star in the night sky and in winter appears over the entire continental United States at one to three fist-widths above the horizon. At dusk, the planet Venus can cause this illusion to occur and many pilots have mistaken it as lights coming from other aircraft.
]
False visual reference
False visual reference illusions may cause the pilot to orient the aircraft in relation to a false horizon; these illusions can be caused by flying over a banked cloud, night flying over featureless terrain with ground lights that are indistinguishable from a dark sky with stars, or night flying over a featureless terrain with a clearly defined pattern of ground lights and a dark, starless sky.
Glassy water landings in seaplanes
Calm glassy water poses a hazard to pilots of seaplane
A seaplane is a powered fixed-wing aircraft capable of takeoff, taking off and water landing, landing (alighting) on water.Gunston, "The Cambridge Aerospace Dictionary", 2009. Seaplanes are usually divided into two categories based on their tec ...
s because the absence of waves hinders accurate judgment of the aircraft's altitude above the water surface on landing. If the pilot overestimates the aircraft's altitude and fails to flare, the tips of the float
Float may refer to:
Arts and entertainment Music Albums
* ''Float'' (Aesop Rock album), 2000
* ''Float'' (Flogging Molly album), 2008
* ''Float'' (Styles P album), 2013
Songs
* "Float" (Tim and the Glory Boys song), 2022
* "Float", by Bush ...
s may be driven into the water, flipping the seaplane; similarly, if the pilot underestimates the aircraft's altitude, flares too high and stalls, the aircraft will pitch down with the same potential result. Glassy water may also result in an unusually clear view of the lake or sea floor and abnormally brilliant reflections of clouds or shore features; these extraneous visual cues may further disorient the pilot. These hazards may be mitigated by flying the final approach over land or parallel to a nearby shoreline, allowing the pilot to use the land as a visual reference; however, the pilot must take care that the presumably shallow landing zone is free of obstructions. In the absence of a suitable landing area near shore, the recommended procedure is to make a long and shallow approach at a slow and steady descent rate and not to attempt to flare; however, the pilot should account for the increased glide and landing distance when using this technique.
Vection
This is when the brain perceives peripheral motion, without sufficient other cues, as applying to itself. Consider the example of being in a car in lanes of traffic, when cars in the adjacent lane start creeping slowly forward. This can produce the perception of actually moving backwards, particularly if the wheels of the other cars are not visible. A similar illusion can happen while taxiing an aircraft.
Repeating pattern
This is when an aircraft is moving at very low altitude over a surface that has a regular repeating pattern, for example ripples on water. The pilot's eyes can misinterpret the altitude if each eye lines up different parts of the pattern rather than both eyes lining up on the same part. This leads to a large error in altitude perception, and any descent can result in impact with the surface. This illusion is of particular danger to helicopter pilots operating at a few metres altitude over calm water.
Examples
* 1965 Carmel mid-air collision
The 1965 Carmel mid-air collision occurred on December 4, 1965, when Eastern Air Lines Flight 853 (N6218C), a Lockheed Super Constellation en route from Boston Logan International Airport to Newark International Airport, collided in mid-air wit ...
, false visual reference illusion (upsloping cloud tops)
* Adam Air Flight 574
Adam Air Flight 574 (KI574 or DHI574) was a scheduled domestic passenger flight operated by Adam Air between the Indonesian cities of Surabaya and Manado that crashed into the Makassar Strait near Polewali in Sulawesi on 1 January 2007. All 102 ...
, graveyard spiral (pilots preoccupied with unrelated equipment failure)
* Alitalia Flight 4128
Alitalia Flight 4128 was a scheduled flight from Leonardo da Vinci Airport, in Rome, Italy, to Palermo International Airport in Palermo, Italy, with 129 on board. On December 23, 1978, it crashed into the Tyrrhenian Sea about north of Palermo wh ...
, black-hole approach illusion
* AIRES Flight 8250
AIRES Flight 8250 was a domestic scheduled passenger flight that on 16 August 2010 crashed on landing at night in poor weather on the Colombian island of San Andrés, killing two of the 131 people on board. The aircraft, an AIRES-operated Boein ...
, black-hole approach illusion
* Air India Flight 855
Air India Flight 855 was a scheduled passenger flight from Santa Cruz Airport, Bombay to Dubai International Airport, Dubai. On New Years Day in 1978, the Boeing 747 operating the flight crashed about off the coast of Bandra, Bombay (now Mum ...
, the leans
* Afriqiyah Airways Flight 771
Afriqiyah Airways Flight 771 was a scheduled international Afriqiyah Airways passenger flight that crashed on 12 May 2010 at about 06:01 local time (04:01 UTC) on approach to Tripoli International Airport, about short of the runway. Of the 10 ...
, head-up illusion
* Atlas Air Flight 3591
Atlas Air Flight 3591 was a scheduled domestic cargo flight under the Amazon Air banner between Miami International Airport and George Bush Intercontinental Airport in Houston. On February 23, 2019, the Boeing 767-375ER(BCF) used for this flig ...
, illusion when accidentally using go around mode
* Copa Airlines Flight 201
Copa Airlines Flight 201 was a regularly scheduled passenger flight from Tocumen International Airport in Panama City, Panama to Alfonso Bonilla Aragón International Airport in Cali, Colombia. On 6 June 1992, the Boeing 737-204 Advanced operatin ...
, the leans
* Flash Airlines Flight 604
Flash Airlines Flight 604 was a charter flight provided by Egyptian private charter company Flash Airlines. On 3 January 2004, the Boeing 737-300 that was operating the route crashed into the Red Sea shortly after takeoff from Sharm El Sheikh ...
, the leans (controversial)
* FlyDubai Flight 981
Flydubai Flight 981 was a scheduled international passenger flight from Dubai International Airport, in the United Arab Emirates, to Rostov-on-Don Airport, Russia. On 19 March 2016, the Boeing 737-800 aircraft serving the flight crashed during a ...
, head-up illusion
* Gulf Air Flight 072
Gulf Air Flight 072 (GF072/GFA072) was a scheduled international passenger flight from Cairo International Airport in Egypt to Bahrain International Airport in Bahrain, operated by Gulf Air. On 23 August 2000 at 19:30Arabia Standard Time (UTC+3 ...
, head-up illusion
* John F. Kennedy Jr. plane crash
John F. Kennedy Jr., the son and namesake of the former U.S. President John F. Kennedy, died when the light aircraft he was flying crashed into the Atlantic Ocean off Martha's Vineyard, Massachusetts, on July 16, 1999. Kennedy's wife Carolyn B ...
, spatial disorientation (controversial)
* Mount Erebus disaster
The Mount Erebus disaster occurred on 28 November 1979 when Air New Zealand Flight 901 (TE-901) flew into Mount Erebus on Ross Island, Antarctica, killing all 237 passengers and 20 crew on board. Air New Zealand had been operating scheduled A ...
, false visual reference illusion (featureless terrain indistinguishable from sky)
* , spatial disorientation
* Roger Peterson (pilot)
On February 3, 1959, American rock and roll musicians Buddy Holly, Ritchie Valens, and The Big Bopper, "The Big Bopper" J. P. Richardson were all killed in a plane crash near Clear Lake, Iowa, together with pilot Roger Peterson. The even ...
, spatial disorientation (controversial)
* Swissair Flight 111, the leans (secondary to electrical fire and multiple equipment failures)
* Tatarstan Airlines Flight 363
Tatarstan Airlines Flight 363 was a scheduled domestic passenger flight, operated by Tatarstan Airlines on behalf of Ak Bars Aero, from Moscow to Kazan, Russia. On 17 November 2013, at local time (UTC+4), the Boeing 737-500 crashed during an a ...
, head-up illusion
* VASP Flight 168
VASP Flight 168, a Boeing 727-212, serial number 21347, registered PP-SRK, was a scheduled passenger flight from São Paulo to Fortaleza, Brazil which, on June 8, 1982, crashed into terrain while descending into Fortaleza, killing all 137 people ...
, black-hole approach illusion
* West Air Sweden Flight 294
West Air Sweden Flight 294 was a cargo flight of a Canadair CRJ200 from Oslo to Tromsø, Norway that crashed on 8 January 2016. A malfunction in one of the inertial reference units had produced erroneous attitude indications on one of the instrume ...
, head-up illusion (secondary to instrument failure)
See also
* Pilot error
Pilot error generally refers to an Aviation accidents and incidents, accident in which an action or decision made by the Aircraft pilot#Airline, pilot was the cause or a contributing factor that led to the accident, but also includes the pi ...
* Brownout
* Spatial disorientation
Spatial disorientation results in a person being unable to determine their position or relative motion, commonly occurring during periods of challenging visibility, since vision is the dominant sense for orientation. The auditory system, vestibular ...
* Bárány chair
The Barany chair or Bárány chair is a device used for aerospace physiology training, particularly for student pilots.
Test
The subject is placed in the chair, blindfolded, then spun about the vertical axis while keeping their head upright or t ...
* Kopp-Etchells effect
* Controlled flight into terrain
In aviation, a controlled flight into terrain (CFIT; usually ) is an aviation accidents and incidents, accident in which an airworthy aircraft, under aircraft pilot, pilot control, is unintentionally flown into the ground, a mountain, a body of ...
References
{{Reflist
External links
FAA Pilot Safety Brochures – Spatial Disorientation (pdf)
FAA Pilot Safety Brochures – Spatial Disorientation – Visual Illusions (pdf)
Pilot’s Handbook of Aeronautical Knowledge, Chapter 17: Aeromedical factors
Aviation risks
Illusions