Download Man`s vestibular and visual system is functionally adapted for life in

Spatial Disorientation in Aviation
Mark Peterson BMed DRACOG FRACGP MFM
1.0
Introduction
Spatial orientation is an essential precondition for situational awareness
in aviation. Sensory perceptions and inferences allow the pilot to form
awareness of the meaning and implications of the current situation, and
the anticipation of future status essential to safe aviation decision
making (Endsley 1999 cited in Rainford, 2006 p.329). Loss of reliable
sensory input and inferences, such as contrasting horizon outlines, has
contributed to major loss of life in aviation, evidenced by the death of
257 people on board Air New Zealand Flight TE901 on Mt Erebus,
Antarctica in 1979 ( Maurino, Reason ,Johnston and Lee, 1995 p.45).
Instrument flight condition accidents associated with disorientation,
account for 28% of pilot fatalities in general aviation (Li and Baker,1999
cited in Li and Baker ,2007). It is generally regarded as being under
reported (Harding and Mills, 1993 p. 88), in part due to the potential for
lethality. Aspects of organizational culture may also inhibit reporting of
disorientation events (Reinhart p.126). Of the 19 hull losses sustained in
the commercial jet accident rate for 2008, 6 were “loss of control”
accidents in which spatial disorientation and loss of situational
awareness in varied forms were likely to have played a major part,
including poor visual references, and initial corrections being in the
wrong direction (Burin, 2010 cited in Flight Safety Australia, 2011, and
Job, 2011).
Human physiology has evolved in a specific terrestrial context which
includes a low velocity body in a largely two-dimensional setting; low
and non-sustained rates of acceleration;1 G of gravity; daylight ; at sea
level partial pressures of oxygen and levels of radiation; with low levels
of vibration, and ambient noise.
Each of these characteristic are altered in the flight environment. The
features of visual and vestibular systems adapted to terrestrial life will be
outlined. Error (or risk) producing phenomena due to limitations in
normal human physiology in the flight environment, will be discussed.
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2.0
Spatial orientation, and visuo-vestibular interactions.
The perceptual inputs into physiological systems for spatial orientation
can be classified as visual, vestibular, and peripheral tissue afferents. All
three classes of inputs interact within the brain to form a orientational
“construct”. The process is complex, involving interaction of the relevant
occipital/ temporal/parietal lobe locations of optic inputs, with vestibular,
cerebellar and brainstem information. Both immediate “head reference”
and gravitational “earth-reference” must include information and
inferences relating to height, direction, position, speed, acceleration,
time. The final orientational “construct” is formed in relation to immediate
surrounds and their meaning, and most importantly to the earth and its
meaning. Confusion of head referenced constructs as being earth
referenced is a major cause of disorientation (such as the coriolis
illusion). The entire process occurs continuously whilst conscious, as
well as being predictive in both time and space. Accurate spatial
orientation is the essential precursor to predictive situational awareness
essential to safe flight.
2.1
Visual orientation.
Visual inputs are usually defined as focal or ambient.
Focal vision requires the central macular functions of the retina, has
good colour and contrast discrimination and excellent image
stabilization. The sensory cells predominant in the foveal and parafoveal
areas of the macula are termed “cones”, and are adapted to
discrimination of fine detail, to object recognition and identification. Focal
vision occurs most efficiently in the central 30 degree field of view, but
effective tracking of focal vision can occur at up to 60 degrees
angulation of the observer to the object. Radiation of focal visual inputs
is via the parvocellular layers of the lateral geniculate body of the
thalamus to the ventral aspect of the primary visual (occipital) cortex,
adjacent to temporal cortex. The parvocellular system comprises 80% of
all optic radiation fibres. The system is termed the “what” system (
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Liebowitz HW and Dichigans J,1980 as cited in Davis JR, 2008 p.148)
.The lateral geniculate body is of particular interest , as it contains
connections to multiple visual, auditory and vestibular inputs that allow
integration of information used in the tracking of visual targets .
Ambient vision uses the more peripheral location of the retina, has poor
colour and contrast discrimation, and is suited to large mobile stimuli
and nocturnal vision. The “rods” are the predominant sensory cells in
this part of the retina. Ambient type vision projects using the
magnocentral pathways via its respective layers of the lateral geniculate
nucleus, to the dorsal occipital cortex (motion) and superior temporal
cortex (form). It is referred to as the “where” system (Liebowitz et
al,1980 as cited in Davis, 2008 p.150). It is also interesting to note that
the dorsal occipital cortex has significant projection to the pontine nuclei
which project to the cerebellar cortex, aiding integration of visual
perception of external movement with the subject’s personal perception
of movement ( Davis,2008 p.149) . Ambient visual cues are less useful
for distance judgment (see below) such as altitude, speed and
ascent/descent, but are highly effective in overall visual orientation in
terrestrial contexts, and in VFR flight.
The cornea provides the majority of refractive power required for
distance vision, with the lens providing lesser refractive power, primarily
for close visual accommodation. In addition, it is noteworthy that the
optic nerve sends a branch to the superior colliculus in the midbrain,
which initiates and regulates orientation movements of the head, eyes
and neck.
Far distance cues that have evolved over evolution and during the
course of an individual experience, are primarily monocular, while close
distance cues ( personal and immediate space less than 10 m and 60 m
respectively) are binocular. The risk producing aspects of terrestrially
originated distance cues will be discussed later on.
2.2
Vestibular Orientation
The main systems for vestibular orientation are the semicircular canals
(SCC’s) for angular motion and the otoliths ( utricle and saccule) which
sit below the SCC’s , for linear acceleration and gravity
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The semicircular canals consist of 3 ducts bilaterally – posterior, anterior
and lateral – of circular canal structures containing hair-like sensory
cells superimposed by a gelatinous cupula. Each canal has a basal
ampulla, which is maximally stimulated by acceleration in the relevant
plane of each canal. All movement stimulates at least 2 of the 3 SCC’s,
or contralateral canals on each side of the head. The inertial resistance
of the cupula endolymph stimulates the hair-like receptors of the SCC’s
during relative movement of the structure. Sensory signals are sent to
the ampullary nerves, and thence to the vestibular nerve via the
vestibular nuclei (Davis, 2008 p.152). Central integration of the signals
from the 3 canals gives inferred information relating to yaw, pitch and
roll, despite the axes of the canals not being specifically in those planes
with respect to the attitude of the head. The thresholds for signal are
highly receptive, being reported as 0.5 degrees/sec ( squared) for
angular motion in the semicircular canls, and 0.1 m/sec ( squared) for
linear acceleration in the otoliths (Rainford, 2006 p 295). The system is
accurate for terrestrial use with typical short motions. Errors typical in
the aviation environment may be produced with steady speed of rotation
for more than a few seconds, or steady increase or decrease in rate of
turn. As soon as the rate of rotations of the cupula becomes constant, it
will register as having returned to neutral position, and at 10-15 secs of
roll, no signal is perceived. Roll cessation after approx 20-30 seconds of
motion produces a recovery error in which a false impression ( equal
intensity) of movement in the opposite direction may arise. In the
aviation environment, this false impression is resolved with continued
straight and level flight (Rainford ,2006 p.297).
The otoliths (utricle and saccule) sit beneath and attached to the SCC’s.
There are two sets, right and left, and the utricles are horizontal in the
upright head, with the saccules being vertical. The otoliths are
responsible for sensory information relating to acceleration in the the
respective plane of the macular cells within each organ. Myelinated
fibres then provide signals to the utricular and saccular nerves, and
thence the vestibular nerves via the vestibular nuclei (Rainford, 2006 p.
295). Its noteworthy that unusual combinations of force in the aviation
environment may cause otolith mediated perceptual error. Gx
acceleration or deceleration may be misinterpreted as having a
component of pitch axis alteration. Major risks occur in the aviation
environment at take–off (especially at night and especially in high
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performance aircraft) when the false “pitch up” perception leads to pilots
enacting inappropriate “pitch down” commands. This can only be
overcome by pilots consciously overriding otolith-mediated pitch
information with visual instrument observed rate of climb/air speed and
pitch attitude information. In practice this amounts to mentally or verbally
rehearsing the possible dangers of night take offs during taxiing, take-off
roll, and in early climb when not clear of obstacles, in order to give
appropriate primacy to internal instrument cues. In terrestrial
environments and in 2 dimensions, these misperceptions are not as
dangerous.
2.3
Visuo-vestibular interactions.
Very close physiological interaction occurs between visual and
vestibular systems. Smooth eye movements such as pursuit, use
vestibular and cerebellar input via brainstem reflexes, as well as ocular
motor cranial nerves nuclei to coordinate eye attention to a target. The
vestibulo-ocular reflex is fundamental to survival in the terrestrial
environment where running and vibration from human movement
degrade target tracking .The reflex occurs with the slow component of
the reflex being the ocular tracking aspect, whilst the rapid component
being vestibular input , initiated in the semicircular canals. In the flying
environment, prolonged spins or rolls leave the vestibular component of
the reflex accurate only in the initial phases. Degradation of object
tracking subsequently occurs, both inside and outside the aircraft
(Rainford, 2006 p.304).
Powerful mechanisms stabilise the retinal image as long as the relative
motion of the target to the subject is less than 60 degrees. At relative
angular disparity above 60 degrees, saccadic eye movement and/or
voluntary head movement is required. Saccadic eye movement is either
reflex or voluntary, assisting ambient peripheral visual tracking when
smooth pursuit eye movements cannot stabilize the retinal image.
An additional interaction between the visual and vestibular system
occurs when linear acceleration induces eye movements via otolith
stimulation – this reflex is less accurate than both smooth pursuit or
saccadic eye movements.
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2.4
Other inputs into spatial awareness – peripheral tissue
afferents
Skin, muscles, tendons, ligaments and joint capsules generate
proprioceptive and tension afferent signals, usually supplied via the
dorsal columns of the spinal cord to brainstem, pons, midbrain ,
cerebellar and thalamic centres integrating sensory signals for spatial
orientation. In addition, sensory signals in the ocular muscles generate
signals used for assisting conjugate gaze (mediated by the longitudinal
fasciculus for the 6th nerve axis) and tracking. Auditory signals, while
important for orientation in the terrestrial environment, are of limited
usefulness for spatial in the noisy and artificial environment of aviation,
apart from use in communications.
3.0
Spacial Disorientation (SD)
Spacial disorientation is the subject of detailed attention in aviation and
is the primary cause of more than 15% of all aviation accidents (Reinhart
,2008 p.126). It is regarded by aviation safety authority Tony Kern
(1998, p.263)) as one of four “killing conditions”, (alongside unexpected
weather deterioration, low flying, and mid-mission planning changes)
that can be addressed by training and flight discipline. A case-control
study of 72 accidents revealed that an initial license acquired above
age 25 years, and not having an instrument rating are each associated
with a 4-fold increased risk of being in a general aviation crash in
instrument meteorological conditions (Groff and Price, 2006). Reporting
of SD is likely to vary inversely according to its lethality , and is also
influenced by organizational culture and training habits of the reporting
group. As of 2003, the USAF and RAF reports of the various types of SD
in military flight vary significantly (Mathews et al 2003 and Holmes et al
2003 cited in Rainford 2006, p.435). The majority SD incidents leading
to accidents are “Type 1”, or unrecognized by the pilot (Rainford, 2006
p.436).
Unlike earthbound situations, the flight environment is three
dimensional, with an additional time dimension having significant
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implications, due to velocities, altitudes and energies far higher than
those experienced during terrestrial evolution. High and sustained rates
of acceleration, multiples of basal gravity, night and non visual
conditions, hypoxic environments, low humidity, high daytime light and
radiation, and high levels of vibration and ambient noise, all contribute to
the malfunction of normal physiology and perception. The classification
of spatial disorientation is somewhat arbitary, as all sensory inputs
ultimately integrate in brainstem, pons, midbrain, thalamus and cortical
structures to produce mental orientation constructs. The limitations of
terrestrial orientation mechanisms in the flight environment are
practically grouped below, as they are experienced in the flight
environment, and by major visual and vestibular mechanisms.
3.1
Visual Disorientation
The flight environment encompasses high speed motion in the dark or
at times almost zero visibility , in 3 dimensions with a big bang at the
end if one gets it wrong. Almost without exception, general visual
orientation is the most reliable source of orientation both within and
without the cockpit. Focal tracking is limited largely by the velocities
inherent in flight, rendering objects far away more significant than would
be the case in normal daily life. The sky has less detail and interest,
lacking the habitual monocular distance cues that orientate us in our
developing years. Seemingly minor details at hugely varying focal
lengths, such as written text combined with dark or distant horizon
scanning, often in low or overstimulated performance settings, can
impact irreversibly on aircraft safety. Visual tasks in flight engender
aspects of fascination , fixation and distraction (Davis,2008 p667) that
can disrupt rational prioritization of tasks, of which being oriented and
“flying the aircraft” is always the primary duty. On the ground one can
always sit down a forget about gravity and altitude for a while, but in
flight , and especially in non dual flying (despite the illusory calm of the
autopilot), disaster is always just a few seconds away. The major
contributors to visual disorientation in the flight environment are
discussed below, although occulogyral and occulogravic illusions are
addressed later, under vestibular illusions.
3.1.1 Focal Object tracking errors.
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The inadequacies of focal scanning and visual acuity in the aviation
setting are very evident in object tracking and collision situations. Such
cues are not always well suited to the non terrestrial velocities of the
flight environment.
Size and angular constancy can be misleading. A collision from
peripheral locations will maintain the same angular location in the visual
field until impact . Focally processed object size remains quite small until
late in the collision process, giving misleading monocular cues,
insufficient to predict and avoid collision in the remaining reaction time
(Green, et al. 1998 p 56). In addition, G forces associated with flight may
cause problem with acuity generated by spectacles and contact lenses,
as well as reduction in the efficiency of head movement for object
tracking. G forces may also lead to major deterioration in visual
orientation and unconsciousness, as noted below. Acuity may also be
reduced by the corneal effects of dry cockpit air, and air at altitude (
Green,R. et al 1996 p.72).
Contrast is important for object discrimination, which has led to modern
Hawk training aircraft in the RAF being painted black to aid rapid visual
location. Severe loss of contrast may occur at night, as well with flight into a
sun low on the horizon, and in other situation of solar glare. Another major
loss of focal contrast cues occurs in flight over water, snow or dust. Absent
focal contrast cues also reduce flat surface perception, and have been
reported in 33-56% of military pilots ( Rainford ,2006 p.435). Focal contrast
cues are also important for ambient vision.
Depth perception at distance is largely a monocular process, with
semiconscious integration of parallax, perspective, relative size, contour
overlap, distance related object colour and clarity cues to estimate depth.
One or several of these cues, such as loss of visibility related aerial image
cues for distance, can vary in the flight environment, and cause false
percepts. Timing issues with accommodation when transferring attention
from within to outside the cockpit create delay of several seconds in
distance vision focus. Poor instrument layouts can place tasks requiring
focal attention in the ambient field of the pilot, leading to further delays and
risks in visual processes.
3.1.2 Ambient cue alteration and disorientation.
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Empty field myopia in an open, low visibility or night sky, occurs quite
naturally in subjects left unchallenged by significant external objects of
focus.The resulting focal point of 1-2 metres is not adequate for aviation
safety. Autokinesis is the perception of false movement of an external
object such as a light when fixation occurs for a prolonged period. The flight
environment can at times lack terrestrial variety, and this phenomenon
occurs more frequently in low variety visual fields (Reinhart, 2008 p.146).
Loss of Horizon used for habitual ambient orientation may also occur due
to sand, snow, or atmospheric conditions. This has been reported in 69-82
% of military pilots (Rainford, 2006 p 435). False horizons and surface
planes (such as linear cloud formations) may give erroneous horizontal
visual references. The lean on the sun illusion may, however, be a more
primitive reflex, with terrestrial instincts relating to the overhead position of
the sun in body attitude, leading a false command of the aircraft to a sunoverhead attitude. This has been reported by 66-75% of military pilots
(Rainford, 2006).
Vection illusions such as strobe lights in clouds can produce angular
illusions, giving misperceptions of linear motion originating from ocular
stimuli. Strobes are also not used in circuit flight and on taxiing, due to the
distracting effect on the ambient vision of the pilot and surrounding aircraft.
Flares and lasers also pose a risk to the ambient environment of the pilots,
as well as a direct retinal blinding effect in some circumstances, and are of
recent topical interest around Australian airports.
3.1.3 Colour alteration
Disorientation may occur if red/green blind pilots require the assistance
of PAPI or VASIS on final approach, and when orienting using coloured
Electronic Flight Instrument Systems (EFIS)
3.1.4 Vibration and visual fixation
Vibration in the aviation environment can be tolerated (as far as object
fixing is concerned) up to a frequency of about 8 HZ by function of
vestibulo-ocular reflexes. Vibratory movement of an object cannot be
9
stabilized by the pilots’ vision above 1HZ. Higher frequencies of vibration
such as 60-90 Hz and 17-25 Hz cause resonance of the eyeball and the
head respectively, further compromising visual acuity.
3.1.5 Gravitational effects unique to aviation.
As indicated above, vision deteriorates from 3.5-4.5 Gz (decay in
peripheral vision), to 4-5Gz (total loss of vision), and ultimately to loss of
consciousness ( G-LOC) at 4-6Gz . This cause of impaired visual
orientation is most relevant to military flight, and aerobatics, particular in
older pilots.
3.1.6 Night flight – specific problems
Physiologic dark adaptation photochemical replacement is a slow, non
linear process, with an initial 1 minute increase in dark adaption of 10
fold becoming a 40 minute dark adaption of 25,000 fold. Pupillary
adaption is more rapid increasing night acuity 30 fold quite quickly. Most
pilots would agree that the human eye, when flying at night, is not the
useful organ it has evolved to be in the daytime. The night blind spot
created by absence of night vision rods in the macular area requires
adaptive off centre tracking techniques at night for pilots. Relative
hypoxia above 5,000 feet (or lower altitudes in the elderly and smokers)
leads to as much as 30% deterioration in night time vision relative to
lower altitudes. Autokinetic illusions are mentioned above, along with
reduced night contrast, increasing disorientation risk at night. Night
myopia occurs, particularly in corrected myopes, as a result of enlarged
pupils and slight involuntary accommodation altering the shape of the
eye, lens and cornea.
Loss of almost all ambient visual cues during a “Black Hole “ night
approach to land, substantially increases risk of SD and loss of aircraft
control. When training, the pilot is required to rely on remaining
instrument cues (attitude, altitude, airspeed and rate of descent) and
external runway light cues, right down to the limited additional
orientation of landing lights during flare just above the runway.
3.1.7 Approach to landing - visual illusions
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Shapes not usually viewed in terrestrial context can lead to depth and
height misperceptions in aviation. Runway width that is narrower than
usual may lead the pilot to infer a high approach, and thus fly lower than
necessary on finals. Conversely, a wide runway may falsely infer a low
approach, leading to a pilot flying an inaccurately high approach. This
latter event will lead to delayed touchdown, and at times missing the
appropriate taxiway at major city airports! Upsloping terrain on approach
may falsely infer greater altitude above the runway than is the case,
leading to an excessively low approach (the converse also applies).
Lack of ground features of appropriate scale may falsely infer greater
altitude than is the case leading to a low approach .This is particularly
true of water approaches (Reinhart, 2008 p.147-149).
3.18 Helicopter flight - specific visual problems in orientation
Another vection illusion is the “waterfall effect” in which helicopter
hovering or slow flight over water can produce the illusion from water
particles in downward motion that the aircraft is climbing relative to the
outside. The wave drift effect is also a vection illusion produced by
hovering in poor visibility, as water or tall grasses is seen to move away
from the aircraft falsely inferring motion in the opposite direction. Lack of
sufficient external visual cues to indicate motion produces the lack of
motion illusion, which may lead the pilot to attempt an unnecessary
increase in airspeed. Significant loss of visual cues also occurs in the
brown-out or white-out effects of rotor wash near landing sites. Night
visual operations using infrared vision with a narrow field of view leads
to the peripheral field of vision inferring a descending trajectory of
objects moving near the aircraft (the crater illusion) when in fact they
are in straight and flight. This produces some added risk for night vision
device (NVD) operations , which are the source of more than 40% of all
SD-related accidents in a USAARL study of military helicopter accidents
(Davis,2008).
3.2 Vestibular disorientation
Terrestrial vestibular orientational cues are regarded as inherently
unreliable in non visual conditions. Pilots are trained to avoid rapid head
movements, and to give active continous priority to visual instrument
cues at night, in instrument conditions, and during transitions to and
11
from VFC to IMC conditions (Kern,998 p267). In flight, vestibular
disorientation risk is worsened by stress, hypoxia, distraction, boredom,
single pilot operations, and advancing pilot age. In general these
disorientations are classified as false perceptions relating to linear
motion or attitude, or false perceptions relating to angular motion and
vertigo (Rainford, 2006 Ch. 28). Vestibular orientation in the flight
environment deals with the added effects of rapid or sustained motion,
at gravities higher than terrestrially experienced, and with the addition of
3 dimensional motion and vibration not normally experienced in the
evolutionary environment.
Its worth noting at the outset that subtle, sub threshold variations in
subject motion, while of lesser importance terrestrially, if remaining
undetected in the flight environment, may have significant implications
for safety due to the multiplication effects of the velocities and energy
inherent in an aircraft in flight.
3.2.1 The “Leans” – false perception of attitude and linear motion
This is regarded as the most common illusion experienced in flight
(Reinhart, 2008 p.139), usually in instrument conditions. Prevalence
rates of 92% (RAF) and 76 % (USAF) are reported (Rainford, 2006
p.435)). A slow undetected turn in these conditions can register as
straight and level (S &L) flight, with subsequent attempts to resume S &
L being erroneously perceived as banking in the opposite direction. The
affected pilot leans in the direction of the original undetected turn, and
tends to re bank the aircraft in that direction. The cause of this
phenomenon is poorly described, and is thought to be due to inaccurate
baseline signals from otolith structures, which can only be oriented (“reset”) by visual means where visual input from instrument orientation is
often inadequate (Rainford,2006 p.448).The problem is usually easily
addressed by the presence of unambiguous external visual cues, but
can be a problem in prolonged IMC flight (not typical of terrestrial
conditions!).
3.2.2 Somatogravic Illusions – false perception of attitude and linear
motion
Errors in attitude perception occur due to confusion of acceleration force
with gravitational force in the flight environment, particularly in IMC
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conditions, although subtle effects occur in VMC flight. Classic lethal
accidents occur, typically post take-off with a 20-30 degree pitch down
attitude, in IMC or night VMC, or IMC after overshoot on landing (
Kern,1999 p.268 and Rainford ,2006 p.445)). These illusions confuse
acceleration as pitch up. Pilots can also confuse deceleration as pitch
down,( leading to a pitch up command risking stall at low level) , or
confuse a coordinated turn as a wings level attitude. Similarly, an aircraft
in a subtle accelerating undetected descent may give an illusory
perception of being more nose high than it is, and pilots may command
a nose down altitudes in response – a response of increased risk for low
level flight, and also glider pilots with low maximum airspeed limits (
Rainford, 2006 p. 445).
Occulogravic illusions also originate in the otolith and are related to
somatogravic illusions. These illusions lead to externally perceived
displacement of visual cues as a result of gravity or linear motion of the
body.The somatogravic illusion of pitch up on acceleration may be
associated, for example, with a perceived upward movement of objects
(termed the “elevator” illusion) within the visual field (Rainford, 2006
p.446).
3.2.3 G- excess illusions - false perceptions of attitude and linear
motion
G excess illusions are a sub group of erroneous sensations produced by
prolonged or atypical sensation of otoliths by large radius turns,
generating illusionary sensations of climbing or diving when moving the
head in pitch axis.
3.2.4
Somatogyral illusions – false perception of angular motion
Constant angular motions at a constant speed will also lead to a gradual
cessation of SCC stimulation, usually over 10-15 seconds. This can lead
to a false sensation of the spin being less intense than it really is. Of
particular danger however is the period of cessation of spinning
movements, when the subject may feel a false perception of spinning in
the opposite direction due to the inertial energy of the cupula continuing
the stimulus in the direction of the original spin. This may led to
overcorrection of the spin recovery in the opposite direction.
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The orientational dangers of spin correction therefore increase with the
length of time of the aircraft’s spin. At the time of spin cessation, the only
reliable sensory inputs are visual (Rainford, 2006 p.449) at a time when
nystagmus may be impairing visual acuity. Spin recovery is no longer a
mandated requirement of non commercial aviation training in Australia.
3.2.5
Oculogyral illusions – false perceptions of angular motion due to
image stabilization failure
Inappropriate signals from the SCC’s also have disorienting effects on
visual perception. External objects fixed at the beginning of a turn or a
roll can create the impression that internal objects moving in unison with
the aircraft (such as the instrument panel) to be moving in the same
plane. Also, on recovery from a turn, objects may be perceived as
moving in the same direction as the erroneous perceptions of the turn.
External objects can be subject to this illusion, with false perceptions of
non turning leading to external lights being perceived as having motions
when in fact they do not. There are reports of aircraft attempting to join
formation with nonmoving lights due to this Illusion!
3.2.6 Coriolis Phenomena (cross-coupling) - false perceptions of
angular movement due to stimulation of semicircular canals.
Coriolis illusions are bizarre vestibular sensations produced by
combined stimulation of multiple axes of the SCC’s . The phenomena
occurs when the relative axes of yaw, pitch and roll are falsely
interpreted as alternate axes due to complexity of head movement – ie a
head movement in roll plus pitch whilst experiencing simultaneous yaw.
The author has experienced this in dark night aviation and it is a
frightening event, risk being resolved only by immediate attention to the
artificial horizon, and by straight and level flight. In Coriolis stimulation, a
“head referenced” action, can be powerfully and falsely attributed as
being “Earth referenced”. The event is usually a major conflict between
SCC and otolith inputs, not normally experienced terrestrially unless one
has labyrinthitis or is rolling down a hill in a barrel! The experience of
motion sickness may also be type of coriolis event, and it is interesting
to note that ballet dancers tend to focus on one object whilst spinning,
presumably in an attempt to achieve a stable head reference whilst
avoiding complex head movements.
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3.2.6
Flicker vertigo and pressure vertigo
These are less common as aviation dangers, however vertigo and
nausea can arise from non biological flickering stimuli often in the 8-10
Hz frequency and usually from instrument clusters, or even from
helicopter rotors. Dysfunction of vestibular systems from pressure
inequalities not usually experienced in terrestrial conditions may trigger
false signals of movement, vertigo, nausea, as well as significant
nystagmus affected visual tracking.
3.3
Postural Disorientations (Reinhart, 2008 p.128)
Unbalanced turns in flight, especially in the climb, with significant
skidding or slipping, can generate tissue and proprioceptive signals that
give the impression of tilting (false earth references).
3.4
Technology and Spatial Disorientation
One final observation is that many accidents occur due to the pilots
forming a false cognitive belief in the accuracy of automated flight
orientation, a form of orientation non existent in our evolutionary history!
Pilots forming an unchallenged belief in the total accuracy of automated
orientation will eventually be found short. Unchecked navigational
computer inputs, false pitot information, false beliefs that an autopilot is
engaged when it is not, or not engaged when it is, lead to dangerous
command decisions overriding even simple visual observation of the
flight attitude indicator. In situations of high stall risk, and when close to
the ground, a false cognitive “ hierarchy” may override practical visual
instrument cues and recovery techniques, leading significant loss of life
(Job, 2011 pp. 60-61).
4.0
Conclusion
Major loss of life still results from spatially disoriented command inputs
in commercial flight, such as the loss of 114 lives of Air Kenya flight KQ
507 in Cameroon in 2007, and 148 lives in the Flash Airlines flight 604
accident at Sharma El-Sheikh, Egypt in 2004 (Job, 2011).
15
It is clear to aviation physiologists that due to our terrestrial evolutionary
environment, humans are not physiologically well adapted to flight.
Since December 17th, 1903 however, pilots unaware of the limitations of
terrestrially originated spatial references, sadly do not escape that same
process of Darwinian natural selection.
16
References
Davis,J., Johnson,R., Stepanek,J., Fogarty,J.(Eds.) Fundamentals of
Aerospace Medicine 4th ed.(2006). Phildelphia. Lippincot
Williams and Wilkins.
Flight Safety Australia. (2011). That was the year that was;
78:44-45 (no author).
Goff,L.S., Price,J.M. (2006). General aviation accidents in degraded
visibility: a case control study of 72 accidents. Aviation Space and
Environmental Medicine,77(10):1062-7.
Green,R.G.,Muir,H.,James,M.,Gradwell,D.,Green,R.L.(1996) Human
Factors for Pilots. Surrey, U.K. Ashgate Publishing.
Harding,R.,Mills,F.(1993).Aviation Medicine. London. BMJ Publishing.
Job,M. (2011). A dark and stormy night - and 90 seconds to disaster.
Flight Safety Australia, May-June,80:58-61.
Kern,T. (1998). Flight Discipline. New York. McGraw Hill.
Li,G., and Baker, S. (2007). Crash Risk in General Aviation. Journal
of the American Medical Association; 297(14): 1596-1598.
Maurino,D.,Reason.J.,Johnston,J.,Lee,R. (1995). Beyond Aviation
Human Factors. Surrey, U.K. Ashgate Publishing.
Rainford,D.J.,Grdwell,D.P.(eds.)(2006). Ernsting’s Aviation Medicine
(4th Ed.) London. Edwin Arnold.
Reinhart,R.O. (2008).Basic Flight Physiology. New York. McGraw
Hill
17
University of Washington,Tacoma. Central visual Pathways Ch. 15,
pp.97-106. Retrieved from
http://courses.washington.edu/psych333/handouts/coursepack/c
h15-Central_vision_pathways.pdf
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