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IFR illusions
About Illusions
What ever the illusion, it will take a few moments for you to get
reoriented. If the illusion occurs in trimmed flight the problem is not as
severe as it might be if it occurs during manoeuvres as it usually does. Spatial
disorientation caused by loss of horizon, change in power, banking, or other
acceleration forces can lead the pilot to believe that the aircraft is doing
something that it is not. These forces cause the pilot’s vestibular and
proprioceptive system to give the somatogravic illusion. A pilots first reaction
will be to over-control in a direction exactly opposite to what should be done.
The only safe procedure during the onset of any illusion is to increase your
instrument scan rate.
We have three orientation
systems. 75% of our orientation is due to our vision. The autokinetic illusion
occurs when a single light is stared at to the point to which it appears to
acquire movement. This can be avoided by a frequent shifting of the eye. A
sloping cloud deck that extends to both sides of your horizon will appear level.
Sloping terrain can give the same illusion. A few lights on a dark mountain can
be confused with stars to give a false horizon
The inner ear is a six-axis gyro system and is most protected part of the body.
Illusions occur when there is a conflict between the visual input and your inner
ear balance. The inner ear reacts to acceleration. A constant acceleration will
cause the inner ear to lose its sensing ability. Once a velocity is attained the
inner ear cannot take a reading. We must rely on vision and our instruments to
ignore the treacherous readings and non-readings of the inner ear. A coordinated
turn, a gradual climb or descent provides no tilting sense to the inner ear. A
roll of two degrees per second may not be sensed by the inner ear.
The motion (vestibular) system
is based on the semicircular canals of the inner ear. The canals detect motions
that are rotary, acceleration, and deceleration. As long as fluids lag the
motion the motion is detected. A less than 2-degrees per second motion cannot be
detected. the most common vestibular illusion is the ‘leans’. A pilot who
discovers a vestibular illusion will most likely react quickly in the opposite
direction. The canals sense the quick motion and will tend to compel you to go
back to the original direction. The entry and failure to recover from both the
graveyard spiral and spin are vestibular illusions.
The otolith organ detects
gravity and is responsible for illusions of motion that simulate gravity.
Acceleration causes to somatogravic illusion. The otolith organ makes you think
that that an excessive climb has occurred, the reaction is to lower the nose
dangerously. Catapult launches cause this illusion. The inversion illusion is
caused when a climbing aircraft levels off. The pilot believes that he is
falling over backwards. The missed approach exposes a pilot to ortholithic
illusions that may cause a pilot to fail to enter a climb due to believing that
level or a descent is a climb. This is due to the acceleration of the aircraft.
The illusion is made even worse as it continues.
Our senses fail when we lack
visual references. An IFR pilot must have the ability to recognize and ignore
the false sensations as they occur. A big part of ability to overcome and ignore
lies in knowing when illusions can occur. Knowledge and understanding of what
can happen is essential to IFR survival.
The proprioceptive system
A
pilot is well advised to fly a normal rectangular pattern at the standard
pattern altitude at night and during periods of poor visibility. Spatial
disorientation caused by illusions are at the top of fatal accident causes.
Runway lights that are brighter than normal give an illusion that they are
closer than they actually are. At night use VASI or a glide slope when possible
to avoid illusions that may fly you into terrain. A narrower runway than you are
normally used to will give an illusion that will cause you to fly a lower final
than is normal or safe. An upslope runway can cause an illusion that you are
high and will cause you to fly a lower final than is normal or safe. Rain on the
windshield will cause an illusion that you are high and will cause you to fly a
lower final than is normal or safe. an approach over water or a dark featureless
area on final will give an illusion of greater height and will cause you to fly
a lower final than is normal or safe. Haze or poor visibility gives an illusion
of greater distance which may cause you to maintain excess altitude.
Night
Lights
Runway and approach light illusions
will always be a problem if you are in an unfamiliar area. For this reason it is
always desirable to make a daylight familiarization flight to an airport before
a first time night arrival. If there is no VASI or VAPI for vertical guidance if
you get too low the runway lights will begin to disappear. A steep approach is
always better at night. If there is a strong crosswind and you are crabbing to
the runway instead of slipping you will get the illusion of being inverted. If
the airport is well lighted in a surrounding dark area you will have an illusion
of being higher than you actually are. Again a steep approach has much
advantage. Rain on the windshield will give the illusion of being higher than
you are. An arrival at an airport with and approach lighting system (ALS) tends
to be lower and at a shallower angle than otherwise. If you are low and pitch
the nose up as a correction or through the use of flaps, the illusion will
indicate that you are rising. Any reduction of power will cause you to land
short.
At night, banking into or away
from a line of lights will give the illusion that a dive or a climb is
occurring. The same dive or climb illusion can happen by a change in aircraft
pitch occurs while flying toward a light. Lights that appear dim, as seen
through haze, will be reported as more distant than they are.
Airport Illusions
You and every other pilot is
susceptible to illusions. When any of our three flight senses (visual, auditory
and kinesthetic) give erroneous information our mind produces inaccurate
information. Flying illusions are most likely to occur at airports due to visual
information. Illusions do not cause accidents. Rather, it is a pilots reaction
to the illusion that precipitates an accident. The best way to overcome the
negative effects of airport illusions is with experience. Even the most
experienced pilot can be fooled.
Our three flying senses fool us
by misinterpreting distances, velocity and relationship. Vision is the number
one creator of illusion. Over our life time of living and flying we have learned
that if two things are of the same size and one appears larger it is nearer. If
we know two lines are parallel then when they appear farther apart that is the
near end. As we fly we learn an approach slope for our aircraft at our home
airport. Our brain has developed a data bank of how things are supposed to be at
airports. The terrain around the airport can also be an illusion creating
factor. Use all the electronic and visual (VASI) help you can get.
You should practice landings at airports of varying width. All too often you
become overly familiar with airports of a consistent length and width. This
familiarity interferes with your perception of an airport of different
dimension. A narrower runway causes an illusion of height; you will fly a lower
approach with a tendency to land short.
Any airport that differs from
our experience because of runway dimension shape or slope is going to give us an
illusion. If a runway slopes away from us our perception (illusion) will be that
we are too low. If you usually fly into narrow runways, a wide runway will give
you a too low illusion. A runway that is more narrow than you are used to will
make you seem high. Using the altimeter along with a standard pattern and
approach procedure resolves both problems. If the runway slopes toward us we
will perceive ourselves as being too high. If we react to the illusion we will
find ourselves both high and long from the anticipated touchdown point. A wide
runway or one whose lights make it appear wider will give the illusion of a low
approach causing the pilot to stay too high.
The atmosphere can create
illusions. Clear clean air makes everything seem closer. Hazy or smog conditions
makes things hard to see and apparently further away. Note: Be aware of this
when reporting distances at strange airports. The effect of sunlight in creating
shadows is an important part of our visual data bank. At night these shadows are
not there. The absence of contrast and background at night is a major cause of
night landing and takeoff accidents. Precipitation will distort visibility
through the windshield and make to think you are higher than you actually are.
Our vision is the major source
of our cues related to speed. However, much of our speed information comes from
our peripheral vision and is often not consciously entered into the brain. The
unfamiliar tangential velocity of the ground passing by in a low level bank may
appear so fast as to make us pull back on the yoke without regard to the air
speed. Stall-spin. This is the classic sequence of the downwind turn from base
to final. We have learned to judge both the proximity and speed of an known
object crossing in front of us. Closer things seem to move faster.
We are all subject to illusion
because we have come to expect certain appearances to occur. When we are told to
look for traffic, we expect to see that traffic. If we don't see the traffic
tension rises; if we see any plane we have our expectation satisfied and we stop
looking. We shouldn't. The traffic we see does not have to be the same traffic
we should be looking for.
A 3 degree approach to an
upslope runway and the illusion is that you are high. The same upslope runway
made narrower and you will find yourself low. A down-slope runway creates a
"low" illusion which can cause long landings on short runways. I have
found the best way to counter airport illusions is to have a constant pattern
procedure based on a stabilized airspeed and full flaps. I know that even in the
worst conditions of illusion I will be close on final.
Pilots unconsciously make
extensive use of their peripheral vision. Level flight, banks, climbs, and
descents rely 80% on peripheral vision. (See downwind turns) At low levels our
peripheral vision gives us a sense of speed. Over time we develop a peripheral
sense as to what "normal" low level speeds are. Add a tailwind, low altitude, a
bank to final approach, and a peripheral sense of a "high" speed. We now have an
illusion causing a pilot response that says to pull back on the yoke to reduce
the speed. The pull merely makes the bank steeper and initiates a low level
stall spin. Recovery not possible. A final approach over high terrain leading to
the runway gives an illusion of a low fast approach. An approach over terrain
that makes the runway seem like an aircraft carrier will give an illusion of too
high and too slow.
Night has its own illusions that
are covered in the night flight lessons. The distance of lights is greatly
affected by the relative clearness and haze existing. A region of no lights such
as might exist off the end of a runway toward the ocean can cause disorientation
because of IFR illusions. The best solution is to go on instruments until
established inland at altitude.
All flying skills, but most
importantly instrument flying requires continual practice. The untrained pilot
who loses visual reference is like going blind. Stress rises and orientation
ceases to exist inside of 20 seconds. You are reluctant to trust your
instruments but failing to do so means a loss of flight control. Every pilot
must, for himself, determine with respect to all the IFR factors of a flight,
the level of acceptable risk. Common sense and caution should reign.
 Where there are no ground features as with water, snow or darkness the
illusion is that the aircraft is at a higher altitude than it really is.
Approaching a downhill runway the illusion is that you are lower than you
really are so you will come in higher.
IFR Precepts
You cannot fly IFR without instruments.
The inner ear is accurate only when supported by visual reference.
Disorientation may take less than 20 seconds.
IFR risk cannot be eliminated but it can be reduced.
You and Illusions
1) Illusions can and do occur to
everyone
2) Proper planning for strange airport conditions is essential
3) Weather and poor visual conditions make strange airport conditions worse.
4) Rely on your instruments to help your sense perceptions
5) Maintain situational awareness, know where you are.
6) Use airport systems and lights for directional and slope help.
7) Your physical condition can make matters better or worse.
Example:
There are some optical illusions that relate to nearby aircraft. An aircraft
below you will appear to be above you. While getting closer it will appear to
descend through your horizon. All the time it is straight an level below you.
Avoid the temptation to dive.
Black Hole Landing
When it is very dark you are subject
to illusions. Your seat position may make you more or less subject to these.
Aircraft seats are situated by a "Design Eye reference Point" (DERP) that is
supposed to give a view over the cowl and at the instrument panel. It is not
marked on the aircraft but is part of the aircraft design.
If your seat is too low during
dark conditions, you will only be able to see runway lights if you are in a
descent. The pilot tends to set up a constant angle for their field of view on
approach. During daylight, you use the "point on the windshield" to maintain
this angle. If the aim point drifts upward you are in an excessive descent; if
it drifts downward you are too high. It works the same at night but the
references are fewer.
The black hole illusion begins
out a few miles on final. The field and lights will be foreshortened. Getting
closer the runway should rise in the field of view. If the aircraft is
descending the foreshortened view will remain constant. The eye/brain
interpretation of this is that the constant foreshortened runway is an
indication of a constant angle approach. This is the "everything is fine"
illusion of the black hole. During the final phases the daytime depth perception
does not work very well.
When flying into a black hole or
‘featureless terrain’ you must use a correctly set altimeter to counter the
illusion. Fly a full pattern using your altimeter and a standardized procedure
for a stabilized approach. This is the best way to assure yourself that you will
not meet an obstacle on final. This is a combined IFR/VFR approach and requires
that you be capable of controlling the aircraft accurately without visual
references. The normal order of viewing runway, lights, and dark areas is so
changed illusions of being higher occur. If the illusions are believed,
touchdown can occur before reaching the runway.
The "black hole illusion" has a
dramatic effect on straight in approaches to a runway. The stabilized constant
angle approach will appear to exist as an illusion while you fly an arc that
flies you into the ground. Do not fly a straight in approach to a runway at
night. Know the pattern altitude. Fly somewhat farther out on down wind than
appears appropriate. Use a standardized configuration approach just as you would
in daytime. Fly the VASI or VAPI if available. Failure to follow the above
recommendations may cause you to make a premature descent. Over flying
featureless terrain without lights on an approach that deprives you of the
height clues can fly you into the ground.
Narrow Runway
A narrow runway can create the
illusion of a high approach. Narrower and shorter than familiar runway will give
illusion that you are higher than you are. Excess speed is most common problem.
Fly the numbers and avoid straight-in arrivals. Prepare for go-around, do it
earlier than usual. The AIM Chapter 8-1-5 states that the pilot who does not
recognize this illusion will adjust his perceived approach path to fly lower.
Once the pilot realizes that he is low it is vital that full power be applied
while maintaining approach speed with yoke pressure. No trim changes. Once the
proper glide path has been intercepted the power can again be reduced and the
stabilized approach resumed.
Wide
Runway
The illusion associated with a wide
runway causes the risk of flaring rather high above the runway with a hard
ground contact to follow.
Down Slope Runway
Gives identical illusion as wide
runway but is much more likely to cause the pilot to over-shoot the runway. A
runway sloping away will give the illusion that you’re low on the approach. A
runway that slopes toward you can give the illusion of height. One of the most
difficult runways is the one with a mound in the middle. This gives the worst of
both illusions.
In landings where you predict
the possibility of illusions, it is vital that you proceed with the landing
using a standard procedure to establish a stabilized approach. The making of
predictable changes of power, flaps, and trim becomes very important as the
landing progresses. ‘Winging’ it for changes in these approach elements means
that you are subjecting yourself to the effects of illusion. A pilot who fails
to recognize illusion is going to make changes as though what he sees is
reality.
Variable Visibility Approach
If, while on approach, you should
suddenly enter an area of reduced visibility you will get an illusion of a
sudden pitch up in aircraft attitude. Failing to recognize this illusion will
lead to an instinctive and abrupt descent in the approach flight path.
Your ability to determine distance is greatly affected by haze. It is not
unusual to call a distance at over twice the actual distance. The sudden
appearance of bright lights during an a night approach through haze will create
the illusion that the airport is much closer than previously realized. This
results in a high approach.
Rain
Rain gives the illusion of being
higher than you actually are. Combined with haze you will fly lower approaches
during rain.
Creating Graveyard Spiral
Have student close eyes, head
forward. Have student try to hold aircraft level. In a few seconds a slight bank
should occur with a gradual increase. There will be a gradual descent, an
increase in airspeed, and an increase in bank angle. Effort of pilot to correct
these will only make them worse.
Lighting Illusions
Pilot mistakes roadways for runways.
Give illusion of being quite close when lights are bright. High approach
results. Low approach results when runway is approached over dark area. Don’t
use landing light until close to ground. The visual cues used for a normal night
landing seem much the same as you get with a rapid increase in sink rate.
After MDA the lights at the
airport get brighter. Illusion is that you will fly right into the lights.
The normal tendency is to fly low when you can't see how high you are.
The more up-slope the runway the lower you must be to appear on the approach
slope
The combination of up-slope and lights makes the situation even worse.
A down-slope will tend to make you high and fast. With lights illusions may
cancel each other.
Rain
Effect
The curve of the aircraft windshield
when impacted by sufficient rain will give a frosted-glass look from the
interior. Heavy rains are accompanied by turbulence, downdrafts and wind shear.
All navigation aids except possibly GPS can be affected by heavy rain. Visual
illusions that can occur require the pilot to pay close attention to altitude,
rates of descent, and aircraft attitude.
Rain greatly increases the noise level in the cockpit and can make all
communication difficult.
Illusions from the rain-covered
windshield can lead the pilot to believe he is high on an approach. The
illusions are of several types such as having a halo around a light, a runway
appearing much shorter than usual or erroneous distance decisions since things
seem further away. Approach lights appear lower. In general, illusions make you
believe you are higher than you actually are, further away than you are actually
are, and lights larger but not brighter. If this is a familiar airport your
preconceptions are very dangerous when in conflict with these illusions.
Reliance on aircraft and navigational instruments are the only safe recourse.
Accept the fact that going from instruments to visual reference in rain is the
most accident-prone region of IFR flight
Vertigo
90% of vertigo related accidents are fatal.
Vertigo occurs when what you see, feels wrong.
The three orientation systems of our body are in conflict as to what has
happened and where we are.
When the three systems are working in conjunction we are comfortable and
oriented.
We are up to 80% dependent upon our eyesight.
Our vestibular (inner ear) system gives us upright, turning and velocity
change feelings.
Our 'butt feeling' is called kinesthetic and gives a sense of gravity.
Vertigo can be of two types, (1) you are unaware of any disorientation, and
(2) when you are aware.
You first must recognize the existence of confusion typical of vertigo.
Once vertigo is recognized, the cure is to force yourself to believe your
instruments.
Believe your instruments but verify that all are operating properly.
Spatial Disorientation
90 percent fatalities when
accident occurs
VFR into IFR most common cause
Then comes flight in marginal VFR
Number three is loss of vacuum pump
--Last major cause is vertigo
Why?
Eyes will believe what your eyes are
preconditioned to see
A slow vacuum pump failure takes about two minutes to be noticed and results
in 80 percent fatality rate.
Declare an emergency
Request direct to nearest VFR or do it on your own.
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