Disorientation
SPATIAL DISORIENTATION AND FATIGUE
Wondai, QLD, a healthy, instrument
rated type experienced pilot flies a perfectly sound Beech King Air into the
ground only seconds after taking off into a clear, resulting in his own death
and that of four of his five passengers.
Pilot education on phenomena such as
spatial disorientation and fatigue is a cornerstone of air safety and is the
first step in avoiding becoming a victim of
‘pilot error’. Fatality rates for pilots are significantly higher in
crashes that occur between 6 p.m. and 5 a.m. and in instrument meteorological
weather conditions (IMC).
This can be attributed partly to
limitations imposed by the human sensory system in flight. The false climb
illusion, also known, as the somatogravic
illusion occurring in dark night take-off, is an example of how limited the
human senses are in flight. Tragic consequences of such illusions can be
minimised by understanding the mechanisms that bring them to the fore.
This article attempts to explain
only a few of the illusions encountered by aviators.
Definitions
Spatial
disorientation is a state characterized by an erroneous orientational
perception, i.e., an erroneous sense of one's position and motion relative to
the plane of the earth's surface.
Geographic
disorientation, or "being lost," is a state characterized by an
erroneous locational percept. These definitions together encompass all the
possible positions and velocities, both translational and rotational, along and
about three orthogonal earth -referenced axes.
Orientation
information includes those parameters that an individual on or near the earth's
surface with eyes open can reasonably be expected to process accurately on a sunny
day. Lateral tilt, forward-backward tilt, angular position about a vertical
axis, and their corresponding first derivatives with respect to time are the
angular positions and motions included; height above ground, forward-backward
velocity, sideways velocity, and up-down velocity are the linear position and
motions included.
Absent
from this collection of orientation information parameters are the location
coordinates, the linear position dimensions in the horizontal plane. In flight,
orientation information is described in terms of flight instrument-based
parameters.
Angular
position is bank, pitch, and heading; and the corresponding angular velocities
are roll rate, pitch rate, and turn rate (or yaw rate). The linear position
parameter is altitude, and the linear velocity parameters are airspeed (or
groundspeed), slip/skid rate, and vertical velocity. In-flight navigation
information is composed of linear position dimensions in the horizontal plane,
such as latitude and longitude or bearing and distance from a navigation
reference point.
TYPES OF
SPATIAL DISORIENTATION
TYPE
I (UNRECOGNIZED)
A disoriented
aviator does not perceive any indication of spatial disorientation. In other
words, he does not think anything is wrong. What he sees—or thinks he sees—is
corroborated by his other senses. Type I disorientation is the most dangerous
type of disorientation. The pilot—unaware of a problem—fails to recognize or
correct the disorientation, usually resulting in a fatal aircraft mishap:
The pilot may see the instruments functioning
properly. There is no suspicion of an instrument malfunction.
There may be no indication of aircraft-control
malfunction. The aircraft is performing normally.
An example of this type of SD would be the
height-/depth-perception illusion when the pilot descends into the ground or
some obstacle above the ground because of a lack of situational awareness.
TYPE
II (RECOGNIZED)
In Type II spatial disorientation, the pilot
perceives a problem (resulting from spatial disorientation). The pilot,
however, may fail to recognize it as spatial disorientation:
The pilot may
feel that a control is malfunctioning.
The pilot may perceive an instrument failure as in the
graveyard spiral, a classic example of Type II disorientation. The pilot does
not correct the aircraft roll, as indicated by the attitude indicator, because
his vestibular indications of straight-and-level flight are so strong.
TYPE
III (INCAPACITATING)
In Type III spatial disorientation, the pilot
experiences such an overwhelming sensation of movement that he or she cannot
orient himself or herself by using visual cues or the aircraft instruments.
Type III spatial disorientation is not fatal if the co-pilot can gain control
of the aircraft.
THE
INNER EAR
Most problems
related to disorientation can be traced to the inner ear, a sensory organ. It's
the key to our ability to balance when on the ground, or to remain oriented in
space when we fly.
VISION
AND THE INNER EAR
The problem
occurs when the outside visual input is obscured, and the seat-of-the-pants
input is ambiguous. Then, you're down to just the output from the inner ear—and
that's when trouble can start. The inner ear is similar to a three-axis gyro.
It detects movement in the roll, pitch, and yaw axes that pilots know so well.
When the sensory outputs of the inner ear are integrated with appropriate
visual references and spatial orientation cues from our bodies, there is little
chance to experience disorientation.
Fluid in the
inner ear reacts only to rate of change, not a sustained change.
For example, when you initiate a banking left turn, your inner ear will detect
the roll into the turn, but if you hold the turn constant, your inner ear will
compensate and rather quickly, although inaccurately, sense that it has
returned to level flight.
SENSORY
ILLUSIONS
As a result,
when you finally level the wings, that new change will cause your inner ear to
produce signals that make you believe you're banking to the right. This
is the crux of the problem you have when flying without instruments in low
visibility weather. Even the best pilots will quickly become disoriented if
they attempt to fly without instruments when there are no outside visual
references. That's because vision provides the predominant and coordinating
sense we rely upon for stability.
Perhaps the most
treacherous thing under such conditions is that the signals the inner ear
produces—incorrect though they may be—feel right!
Perhaps the most
treacherous thing under such conditions is that the signals the inner ear
produces—incorrect though they may be—feel right!
INSTRUMENT
FLYING
The obvious
method to prevent disorientation is the instrument rating. But, that rating
alone is no automatic guarantee, because there is no such thing as
"knowing how to fly on instruments." You must continue to practice
your skills. You are either formally trained and current—or you are
unqualified.
So, don't try to
fly through a cloudbank or "scud-run" in low visibility conditions if
you aren't a current, instrument-rated pilot. For the unqualified pilot, the
sudden loss of visual reference is similar to a sudden loss of eyesight. All
pilots should check the weather conditions and use good judgment in flight
planning. The VFR pilot should avoid low visibility conditions, such as night
flying, fog, clouds, and haze. And, if you're instrument-rated and current, you
should always trust your instruments. Those gyros are much more reliable than
the ones inside your head.
GRAVEYARD
SPIN
·
This illusion usually occurs in fixed-wing aircraft.
·
For example, a pilot
enters a spin and remains in it for several seconds.
·
The pilot’s semicircular canals reach equilibrium; no motion
is perceived
·
Upon recovering from
the spin, the pilot undergoes deceleration, which is sensed by the semicircular
canals.
·
The pilot has a strong
sensation of being in a spin in the opposite direction even if the flight
instruments contradict that perception.
·
If deprived of external visual references, the pilot may
disregard the instrumentation and make control corrections against the falsely
perceived spin. The aircraft will then re-enter a spin in the original
direction.
A MISJUDGED
APPROACH
In flight, the visual and vestibular
systems play a dominant role in perceiving orientation. Visual processing
involves focal and ambient modes of processing. Focal
vision uses the central 30 degrees of the visual fields and is important for
resolution of fine detail of the visual image. This mode of vision is adopted
when reading flight instruments. Ambient vision determines orientation to the
environment using the peripheral visual field. This process occurs without
being consciously aware of the employed visual cues.
When flying in instrument
meteorological weather conditions, a pilot is more likely to misjudge his or
her approach. This occurs because flight instruments (focal vision) have to be
used in orientating the aircraft. On land ambient vision is adopted for
orientation. As a result, greater brain processing when using the focal mode of
vision for orientation is required. This skill has to be learnt.
Illusions involving focal vision
include shape constancy: runway slope illusions; size constancy: runway width
illusions and the effect of the slope of the terrain under the approach on the
approach slope. Illusions involving ambient vision include the black hole
approach and solitary lights in the dark appearing to move although stationary.
THE
"false climb" ILLUSION
The vestibular apparatus is a
sensory receptor located in the ears, and is involved in maintaining balance. This
organ of balance is about the size of a pea, but can be stimulated by angular
accelerations of 0.9 mrad/s2 and linear accelerations of 0.1m/s2.
This organ can be divided into two:
§
The semicircular canals responsible for angular acceleration
and the otolith organs responsible for linear acceleration.
§
Otolith organs provide the brain with information about the
position of the head by sensing the direction of gravity acting on them. The
brain interprets the information from the otoliths in conjunction with visual
cues. When visual cues are insufficient, the false climb illusion, also known
as the somatogravic illusion, occurs.
On land, gravity and visual cues act
on the otoliths to provide the correct information on head position. When
taking off on dark night, visual cues from the runway give correct information
to the brain thus no illusions occur. Once the aircraft is rotated and starts
to climb, gravity and straight-line acceleration combine to give a resultant
force. The otolith organs sense this resultant force.
The resultant force makes the pilot
feel that he is in a higher nose attitude than he is. Because on a dark night
or in bad weather there is inadequate outside reference, the illusion causes the
pilot to ‘correct’ the apparent nose-up attitude.
The ‘corrections’ cause more
acceleration and a worsening of the illusion, with dire consequences. Tragic
consequences of the false climb illusion can be avoided by an effective
instrument scan, maintaining Vx, and being especially careful when
flying from, or into, unfamiliar runways on dark nights.
THE LEANS
The most commonly
reported manifestation of spatial disorientation is the leans. Almost all
pilots have experienced this form of disorientation. It occurs frequently with
recovery from a co-ordinated turn to level flight when flying by instruments.
lt is a false sense of roll attitude.
The illusion occurs when
a pilot drops one wing at a rate that is below the threshold for detection of a
change in angular velocity. The linear acceleration occurs smoothly enough for
the otoliths to not be stimulated, thus the brain still believes the aircraft
to be level. The error is noticed on instruments and the aircraft quickly
rolled back to wings level.
The information
transmitted to the brain gives the illusion of roll attitude. Information on
the instruments and what the brain thinks then conflict. The pilot then leans
in the direction of the original sub-threshold roll in order that he/she aligns
his/her body with the perceived vertical. The brain eventually recognises what
attitude it is actually in but until that time, attention must be paid to the
attitude indicator. Minimising head movements, maintaining a high proficiency
in instrument flying and transition onto instruments early are ways of avoiding
this illusion.
FALSE
HORIZON ILLUSION
The false
horizon illusion occurs when the aviator confuses cloud formations with the
horizon or the ground. This illusion occurs when an aviator subconsciously chooses
the only reference point available for orientation. A sloping cloud deck may be
difficult to perceive as anything but horizontal if it extends for any great
distance in the pilot’s peripheral vision. An aviator may perceive the
cloudbank below to be horizontal although it may not be horizontal to the
ground; thus, the pilot may fly the aircraft in a banked attitude. This
condition is often insidious and goes undetected until the aviator recognizes
it and makes the transition to the instruments and corrects it. This illusion
can also occur if an aviator looks outside after having given prolonged
attention to a task inside the cockpit. The confusion may result in the aviator
placing the aircraft parallel to the cloudbank.
HEIGHT-DEPTH
PERCEPTION ILLUSION
The height-depth
perception illusion is due to a lack of sufficient visual cues and causes an
aircrew member to lose depth perception. Flying over an area devoid of visual
references—such as desert, snow, or water—will deprive the aircrew member of
his perception of height. The aviator, misjudging the aircraft’s true altitude,
may fly the aircraft dangerously low in reference to the ground or other
obstacles above the ground. Flight in an area where visibility is restricted by
fog, smoke, or haze can produce the same illusion.
RECOMMENDATIONS
Spatial disorientation
can’t be totally eliminated. However, aircrew members need to remember that
misleading sensations from sensory systems are predictable. These sensations
can happen to anyone because they are due to the normal functions and
limitations of the senses. Training, instrument proficiency, good health, and
aircraft design minimize spatial disorientation. Spatial disorientation becomes
dangerous when pilots become incapable of making their instruments read right.
All pilots, regardless of experience level, can experience spatial
disorientation
- Never fly without visual
reference points (either the actual horizon or the artificial horizon
provided by the instruments).
- Trust the instruments.
- Avoid fatigue, smoking,
hypoglycaemia, hypoxia, and anxiety, which all heighten illusions.
- Never try to fly VMC and IMC at
the same time
- Refer to the instruments and
develop a good crosscheck.
- Delay intuitive actions long
enough to check both visual references and instruments.
- Transfer control to the other
pilot if two pilots are in the aircraft. Rarely will both experience
disorientation at the same time.
- Don't try to fly through a cloudbank or
"scud-run" in low visibility conditions if you aren't a current,
instrument-rated pilot.
FATIGUE
A review of the Aviation Safety
Reporting System reported that fatigue was cited as a factor in 20% of reported
incidents. Fatigue causes decreased concentration. The combination of fatigue,
positive G-forces and oxygen deficiency is known to negatively influence
vision. Thus, the addition of this negative influence to spatial disorientation
could have disastrous consequences.
Disruptions in wake-sleep
rhythms, particularly induced by sleep deprivation, are limiting factors for aviators.
Diurnal biochemical reactions occurring at set times during the day and night
is affected by sleep deprivation and fatigue. Long-haul flights across time
zones result in desynchronisation of the sleep/wake cycle, leading to
compromised cognitive ability. As a rule of thumb, it takes one day per time
zone crossed to recover from jet lag.
The role of sleep and naps in the recovery of performance is generally
accepted. The combination of naps and certain pharmacological aids has been
investigated and found improve cognitive performance during sleep deprivation.
Below are extracts from a
South African aircraft accident report, in which the pilot was fatally injured,
and of which the probable cause was attributed to that of “disorientation”.
ZS-TOM accident number 7331
The
aircraft took-off from Springbok Aerodrome to Springs Aerodrome early in the
morning under typical night conditions when the Eastern sky just started
lighting up.
The
aircraft entered a tight left-hand turn after take-off and impacted the
mountain initially with its right-hand wing and rolled over to impact the top
surface of the mountain in an inverted attitude. The pilot was fatally injured during the
impact.
No
defects were detected with the aircraft or it’s systems.
Although the pilot was
night rated he had not flown in night conditions in the last 23 months.
Additional Information
1. A quote from “Human Factors for
Aviation” relates to the effect of disorientation as follows: We start
with a cautionary note. Disorientation can happen to anyone, even
instrument-rated pilots. However, non-instrument-rated pilots are much more
prone to it. Disorientation is also one of the most common reasons why pilots
have accidents. It is not only very unsettling, but also extremely dangerous
to lose orientation when flying. It is also very easy. In fact, it is
impossible to maintain orientation when flying using the body's sensory organs
alone, unless you can see the horizon.
2 In the book “The Pilot’s Night Flying
Handbook” the writer describes:
The inner ear is an extremely
sensitive indicator. Walk across a room with eyes closed and your progress should
be as nearly true as when your eyes are open. As you move, three semicircular
canals in each ear sense any position error and signal the brain to make
corrections through the muscles. As seen in Figure 57, the canals function in
any dimension because they lie at right angles to each other. They generate
signals through moving fluids, which stimulate nerve endings within each canal.
3 The semicircular canals are sensitive
to changes in the body's angular motion; a companion structure responds
to linear motion, or acceleration and deceleration. It's done by a sac
of tiny granules, which presses against nerve endings in the static organ (Fig
58) as the body moves. Scientists believe this elegant sensory equipment
evolved eons ago to accommodate one of the most fundamental human
characteristics: the ability to walk
upright.
4 But the delicate sensory equipment is
linked to earth walking, not airplane flying. The forces of flight easily fool
the inner ear into sending the wrong directional signals. Because of inertia,
inner-ear fluids cannot detect very slight changes of an airplane's attitude
and fail to sense a gentle turn. Too, they are unable to perceive attitude
changes if they occur at a constant rate. Even if a pilot suddenly realizes his
airplane's attitude is wrong, his problem isn't over. If he tries to recover
without seeing the horizon, inner-ear fluids spill beyond their rest position
and tell the pilot he is now entering a similar maneuver, but in the opposite
direction!
5 Vertigo is a killer but for the wrong
reasons. Its confusion can be cured in
moments by simple procedures.
Catastrophe happens when a pilot believes his body’s false signals and
attempts to fly the airplane solely by feeling. Uncertainty develops into panic
if the eyes catches sight of outside lights and tries to form a coherent
picture. During this sensory struggle
the plane escapes control and chances of recovery rapidly fade.
Sources
- RICHARD M HARDING, FJ
MILLS - AVIATION MEDICINE THIRD EDITION
PAGE 87 TO 100
- RECHARD O, REINHARD, FIT
FOR FLIGHT SECOND EDITION
PAGE: 57 TO 78
·
TROLLIP, S.R & JENSEN, RS – HUMAN FACTORS FOR GENERAL
AVIATION, 1991.
·
ZS-TOM, SA-CAA ACCIDENT NUMBER 7331