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Graveyard Spiral
As in other illusions, a pilot in a prolonged coordinated,
constant rate turn, will have the illusion of not turning.
During the recovery to level fl ight, the pilot will experience
the sensation of turning in the opposite direction. The
disoriented pilot may return the aircraft to its original turn.
Because an aircraft tends to lose altitude in turns unless the
pilot compensates for the loss in lift, the pilot may notice
a loss of altitude. The absence of any sensation of turning
creates the illusion of being in a level descent. The pilot may
pull back on the controls in an attempt to climb or stop the
descent. This action tightens the spiral and increases the loss
of altitude; hence, this illusion is referred to as a graveyard
spiral. [Figure 1-7] At some point, this could lead to a loss
of control by the pilot.
Somatogravic Illusion
A rapid acceleration, such as experienced during takeoff,
stimulates the otolith organs in the same way as tilting the
head backwards. This action creates the somatogravic illusion
of being in a nose-up attitude, especially in situations without
good visual references. The disoriented pilot may push the
aircraft into a nose-low or dive attitude. A rapid deceleration
by quick reduction of the throttle(s) can have the opposite
effect, with the disoriented pilot pulling the aircraft into a
nose-up or stall attitude.
Inversion Illusion
An abrupt change from climb to straight-and-level fl ight 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.
Elevator Illusion
An abrupt upward vertical acceleration, as can occur in
an updraft, can stimulate the otolith organs to create the
illusion of being in a climb. This is called elevator illusion.
The disoriented pilot may push the aircraft into a nose-low
attitude. An abrupt downward vertical acceleration, usually
1-7
Figure 1-8. Sensations From Centrifugal Force.
in a downdraft, has the opposite effect, with the disoriented
pilot pulling the aircraft into a nose-up attitude.
Visual Illusions
Visual illusions are especially hazardous because pilots rely
on their eyes for correct information. Two illusions that lead
to spatial disorientation, false horizon and autokinesis, are
concerned with only the visual system.
False Horizon
A sloping cloud formation, an obscured horizon, an aurora
borealis, a dark scene spread with ground lights and stars,
and certain geometric patterns of ground lights can provide
inaccurate visual information, or false horizon, for aligning
the aircraft correctly with the actual horizon. The disoriented
pilot may place the aircraft in a dangerous attitude.
Autokinesis
In the dark, a stationary light will appear to move about when
stared at for many seconds. The disoriented pilot could lose
control of the aircraft in attempting to align it with the false
movements of this light, called autokinesis.
Postural Considerations
The postural system sends signals from the skin, joints, and
muscles to the brain that are interpreted in relation to the
Earth’s gravitational pull. These signals determine posture.
Inputs from each movement update the body’s position to
the brain on a constant basis. “Seat of the pants” fl ying is
largely dependent upon these signals. Used in conjunction
with visual and vestibular clues, these sensations can be
fairly reliable. However, because of the forces acting upon
the body in certain fl ight situations, many false sensations
can occur due to acceleration forces overpowering gravity.
[Figure 1-8] These situations include uncoordinated turns,
climbing turns, and turbulence.
Demonstration of Spatial Disorientation
There are a number of controlled aircraft maneuvers a pilot
can perform to experiment with spatial disorientation. While
each maneuver will normally create a specifi c illusion, any
false sensation is an effective demonstration of disorientation.
Thus, even if there is no sensation during any of these
maneuvers, the absence of sensation is still an effective
demonstration in that it shows the inability to detect bank
or roll. There are several objectives in demonstrating these
various maneuvers.
1. They teach pilots to understand the susceptibility of
the human system to spatial disorientation.
2. They demonstrate that judgments of aircraft attitude
based on bodily sensations are frequently false.
3. They help lessen the occurrence and degree of
disorientation through a better understanding of the
relationship between aircraft motion, head movements,
and resulting disorientation.
4. They help instill a greater confi dence in relying on
fl ight instruments for assessing true aircraft attitude.
1-8
A pilot should not attempt any of these maneuvers at low
altitudes, or in the absence of an instructor pilot or an
appropriate safety pilot.
Climbing While Accelerating
With the pilot’s eyes closed, the instructor pilot maintains
approach airspeed in a straight-and-level attitude for several
seconds, and then accelerates while maintaining straight-andlevel
attitude. The usual illusion during this maneuver, without
visual references, will be that the aircraft is climbing.
Climbing While Turning
With the pilot’s eyes still closed and the aircraft in a straightand-
level attitude, the instructor pilot now executes, with a
relatively slow entry, a well-coordinated turn of about 1.5
positive G (approximately 50° bank) for 90°. While in the
turn, without outside visual references and under the effect of
the slight positive G, the usual illusion produced is that of a
climb. Upon sensing the climb, the pilot should immediately
open the eyes and see that a slowly established, coordinated
turn produces the same feeling as a climb.
Diving While Turning
Repeating the previous procedure, with the exception that
the pilot’s eyes should be kept closed until recovery from
the turn is approximately one-half completed can create this
sensation. With the eyes closed, the usual illusion will be
that the aircraft is diving.
Tilting to Right or Left
While in a straight-and-level attitude, with the pilot’s eyes
closed, the instructor pilot executes a moderate or slight skid
to the left with wings level. This creates the illusion of the
body being tilted to the right.
Reversal of Motion
This illusion can be demonstrated in any of the three planes of
motion. While straight and level, with the pilot’s eyes closed,
the instructor pilot smoothly and positively rolls the aircraft to
approximately a 45° bank attitude while maintaining heading
and pitch attitude. This creates the illusion of a strong sense
of rotation in the opposite direction. After this illusion is
noted, the pilot should open his or her eyes and observe that
the aircraft is in a banked attitude.
Diving or Rolling Beyond the Vertical Plane
This maneuver may produce extreme disorientation. While
in straight-and-level fl ight, the pilot should sit normally,
either with eyes closed or gaze lowered to the fl oor. The
instructor pilot starts a positive, coordinated roll toward a
30° or 40° angle of bank. As this is in progress, the pilot
tilts his or her head forward, looks to the right or left, then
immediately returns his or her head to an upright position.
The instructor pilot should time the maneuver so the roll is
stopped as the pilot returns his or her head upright. An intense
disorientation is usually produced by this maneuver, and the
pilot experiences the sensation of falling downward into the
direction of the roll.
In the descriptions of these maneuvers, the instructor pilot is
doing the fl ying, but having the pilot do the fl ying can also
be a very effective demonstration. The pilot should close his
or her eyes and tilt the head to one side. The instructor pilot
tells the pilot what control inputs to perform. The pilot then
attempts to establish the correct attitude or control input with
eyes closed and head tilted. While it is clear the pilot has no
idea of the actual attitude, he or she will react to what the
senses are saying. After a short time, the pilot will become
disoriented and the instructor pilot then tells the pilot to
look up and recover. The benefi t of this exercise is the pilot
experiences the disorientation while fl ying the aircraft.
Coping with Spatial Disorientation
To prevent illusions and their potentially disastrous
consequences, pilots can:
1. Understand the causes of these illusions and remain
constantly alert for them. Take the opportunity to
understand and then experience spatial disorientation
illusions in a device such as a Barany chair, a
Vertigon, or a Virtual Reality Spatial Disorientation
Demonstrator.
2. Always obtain and understand preflight weather
briefi ngs.
3. Before fl ying in marginal visibility (less than 3 miles)
or where a visible horizon is not evident such as fl ight
over open water during the night, obtain training and
maintain profi ciency in airplane control by reference
to instruments.
4. Do not continue fl ight into adverse weather conditions
or into dusk or darkness unless profi cient in the use of
fl ight instruments. If intending to fl y at night, maintain
night-fl ight currency and profi ciency. Include crosscountry
and local operations at various airfi elds.
5. Ensure that when outside visual references are used,
they are reliable, fi xed points on the Earth’s surface.
6. Avoid sudden head movement, particularly during
takeoffs, turns, and approaches to landing.
7. Be physically tuned for fl ight into reduced visibility.
That is, ensure proper rest, adequate diet, and, if fl ying
at night, allow for night adaptation. Remember that
illness, medication, alcohol, fatigue, sleep loss, and
mild hypoxia are likely to increase susceptibility to
spatial disorientation.
1-9
Water Refraction
Rain on the windscreen can create an illusion of being at a
higher altitude due to the horizon appearing lower than it is.
This can result in the pilot fl ying a lower approach.
Haze
Atmospheric haze can create an illusion of being at a greater
distance and height from the runway. As a result, the pilot
will have a tendency to be low on the approach. Conversely,
extremely clear air (clear bright conditions of a high attitude
airport) can give the pilot the illusion of being closer than he
or she actually is, resulting in a high approach, which may
result in an overshoot or go around. The diffusion of light
due to water particles on the windshield can adversely affect
depth perception. The lights and terrain features normally
used to gauge height during landing become less effective
for the pilot.
Fog
Flying into fog can create an illusion of pitching up. Pilots
who do not recognize this illusion will often steepen the
approach quite abruptly.
Ground Lighting Illusions
Lights along a straight path, such as a road or lights on moving
trains, can be mistaken for runway and approach lights. Bright
runway and approach lighting systems, especially where
few lights illuminate the surrounding terrain, may create the
illusion of less distance to the runway. The pilot who does not
recognize this illusion will often fl y a higher approach.
How To Prevent Landing Errors Due to
Optical Illusions
To prevent these illusions and their potentially hazardous
consequences, pilots can:
1. Anticipate the possibility of visual illusions during
approaches to unfamiliar airports, particularly at
night or in adverse weather conditions. Consult
airport diagrams and the Airport/Facility Directory
(A/FD) for information on runway slope, terrain, and
lighting.
2. Make frequent reference to the altimeter, especially
during all approaches, day and night.
3. If possible, conduct aerial visual inspection of
unfamiliar airports before landing.
8. Most importantly, become profi cient in the use of
flight instruments and rely upon them. Trust the
instruments and disregard your sensory perceptions.
The sensations that lead to illusions during instrument
fl ight conditions are normal perceptions experienced by
pilots. These undesirable sensations cannot be completely
prevented, but through training and awareness, pilots can
ignore or suppress them by developing absolute reliance
on the flight instruments. As pilots gain proficiency in
instrument fl ying, they become less susceptible to these
illusions and their effects.
Optical Illusions
Of the senses, vision is the most important for safe fl ight.
However, various terrain features and atmospheric conditions
can create optical illusions. These illusions are primarily
associated with landing. Since pilots must transition from
reliance on instruments to visual cues outside the fl ight
deck for landing at the end of an instrument approach, it is
imperative they be aware of the potential problems associated
with these illusions, and take appropriate corrective action.
The major illusions leading to landing errors are described
below.
Runway Width Illusion
A narrower-than-usual runway can create an illusion the
aircraft is at a higher altitude than it actually is, especially
when runway length-to-width relationships are comparable.
[Figure 1-9A] The pilot who does not recognize this illusion
will fl y a lower approach, with the risk of striking objects
along the approach path or landing short. A wider-than-usual
runway can have the opposite effect, with the risk of leveling
out high and landing hard, or overshooting the runway.
Runway and Terrain Slopes Illusion
An upsloping runway, upsloping terrain, or both, can create
an illusion the aircraft is at a higher altitude than it actually
is. [Figure 1-9B] The pilot who does not recognize this
illusion will fl y a lower approach. Downsloping runways and
downsloping approach terrain can have the opposite effect.
Featureless Terrain Illusion
An absence of surrounding ground features, as in an
overwater approach, over darkened areas, or terrain made
featureless by snow, can create an illusion the aircraft is at
a higher altitude than it actually is. This illusion, sometimes
referred to as the “black hole approach,” causes pilots to fl y
a lower approach than is desired.
1-10
Figure 1-9. Runway Width and Slope Illusions.
6. Recognize that the chances of being involved in an
approach accident increase when some emergency or
other activity distracts from usual procedures.
7. Maintain optimum profi ciency in landing procedures.
4. Use Visual Approach Slope Indicator (VASI) or
Precision Approach Path Indicator (PAPI) systems
for a visual reference, or an electronic glide slope,
whenever they are available.
5. Utilize the visual descent point (VDP) found on many
nonprecision instrument approach procedure charts.
1-11
Figure 1-10. Stress and Performance.
Physiological and Psychological Factors
Physiological or psychological factors can affect a pilot
and compromise the safety of a fl ight. These factors are
stress, medical, alcohol, and fatigue. Any of these factors,
individually or in combination, signifi cantly degrade the
pilot’s decision-making or fl ying abilities.
Stress
Stress is the body’s response to demands placed upon it. These
demands can be either pleasant or unpleasant in nature. The
causes of stress for a pilot can range from unexpected weather
or mechanical problems while in fl ight, to personal issues
unrelated to fl ying. Stress is an inevitable and necessary part
of life; it adds motivation to life and heightens an individual’s
response to meet any challenge. The effects of stress are
cumulative and there is a limit to a person’s adaptive nature.
This limit, called the stress tolerance level (or channel
capacity), is based on the ability to cope with the situation.
At fi rst, some amount of stress can be desirable and can
actually improve performance. However, higher stress levels,
particularly over long periods of time, can adversely affect
performance. Performance will generally increase with the
onset of stress, but will peak and then begin to fall off rapidly
as stress levels exceed the ability to cope. [Figure 1-10]
At this point, a pilot’s performance begins to decline and
judgment deteriorates. Complex or unfamiliar tasks require
higher levels of performance than simple or overlearned
tasks. Complex or unfamiliar tasks are also more subject to
the adverse effects of increasing stress than simple or familiar
tasks. [Figure 1-10]
The indicators of excessive stress often show as three types
of symptoms: (1) emotional, (2) physical, and (3) behavioral.
Emotional symptoms may surface as over-compensation,
denial, suspicion, paranoia, agitation, restlessness, or
defensiveness. Physical stress can result in acute fatigue
while behavioral degradation will be manifested as sensitivity
to criticism, tendency to be argumentative, arrogance, and
hostility. Pilots need to learn to recognize the symptoms of
stress as they begin to occur.
There are many techniques available that can help reduce
stress in life or help people cope with it better. Not all of the
following ideas may be a solution, but some of them should
be effective.
1. Become knowledgeable about stress.
2. Take a realistic self-assessment. (See the Pilot’s
Handbook of Aeronautical Knowledge).
3. Take a systematic approach to problem solving.
4. Develop a lifestyle that will buffer against the effects
of stress.
5. Practice behavior management techniques.
6. Establish and maintain a strong support network.
Good fl ight deck stress management begins with good life
stress management. Many of the stress coping techniques
practiced for life stress management are not usually practical
in fl ight. Rather, pilots must condition themselves to relax and
think rationally when stress appears. The following checklist
outlines some methods of fl ight deck stress management.
1. Avoid situations that distract from fl ying the aircraft.
2. Reduce fl ight deck workload to reduce stress levels.
This will create a proper environment in which to make
good decisions. Typically, fl ying involves higher stress
levels during takeoff and landing phases. Between the
two generally lies a period of low activity resulting
in a lower stress level. Transitioning from the cruise
phase to the landing phase is generally accompanied
by a significant workload that, if not properly
accommodated, will increase stress significantly.
Proper planning and prioritization of flight deck
duties are key to avoiding events that affect the pilot's
capacity to maintain situational awareness. |
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发表于 2008-12-9 15:29:24
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