Consider the wording “graveyard
spiral”. It is a concept so scary that your mind wants you to look elsewhere,
maybe the ads on the next page. We will see how it starts but lets first see
how it would terminate. Given the right circumstance (discussed below) the
g-forces accumulate in a fury and exceed the structural integrity of the
airframe causing disintegration or as NASA would call it a “system anomaly”. A
1954 study by the Air Safety Foundation revealed 19 of the 20 pilots who
inadvertently entered the graveyard spiral in IMC lost control of aircraft and
life. The average time of entering IMC and entry into spiral was 178 seconds.
Chilling! And to boot 5-10% of GA accidents are attributed to loss of control
due to spatial disorientation and 90% are associated with loss of life.
Space is certainly a frontier that
has all to do with visual control. As long as the VFR mind can see the blue
above and the green/brown below it is happy. Void the visual cues and the
mind’s reliance falls on unreliable senses. So the eyes have it and they
control 90% or greater sensitivity in orienting to space. This is by virtue of
visual cues. Consider flying VFR on top on a sloping cloud deck and before you
know it you would have banked the aircraft to align with the slope. The
perceived rate of error can build at the rate of 0.2-0.3 degrees per second.
The accumulation of these errors creates the spiral. The pilot thinks he /she
is flying straight and level all the time never once considering the
instruments crying for his/her attention. By that time the ears and the seat of
your sweat-drenched trousers are crying foul and damn-it there is utter
confusion and chaos because you have never felt this before. You tug, pull and
push and complicate a situation already maximally torqued out of form and there
you have a full-blown spiral looking at a graveyard.
Lets look at the psychophysics of
this event: The pilot is stationary and restrained in his seat with seat belts.
The space around him is spinning and out of control. In these circumstances
susceptibility to imbalance is unrelated. The inputs placed by the pilot are
relational to experience and performance. The susceptibility to spatial
disorientation is inane to human. It is the belief placed on the virtual
environment enclosed in a grayed space of clouds where the instrument represent
and depict the space around us that we have to learn, believe and then react
to, that influences our navigation behavior and thus helps keep us from a
system anomaly.
The Human ADHRS and its microcomponents
Driving a car is a 2 dimensional
space requires “Wayfinding” and
motion to achieve the desired result of arriving at a destination. Driving a
car on a banked highway prevents the centrifugal force to uproot the tires off
the road. Trying to straighten the car on that banked road will lead to
unpleasant results. Flying a plane is similar only in 3 dimensions. The banked
highway in the sky is an interpolation of aeronautical facts, spatial
orientation and a balance of the four forces of flight. Nowadays the mental
maps of airspace are virtually depicted on the computer screens in the cockpit
hence the positional loss is a remote error at best, unless the computer gives
up the ghost and we have a spine chilling lack of situational awareness
euphemistically called RAIM loss. That RAIM loss is nothing but satellite
chatter providing pseudo-vectors due to downtime as there are not enough of
them to provide guidance. With the GPS functional and given that we know where
we are the next step is to make sure we are right side up all the time. That is
a dependence on the attitude indicator along with a democratic concert with the
other five standard equipments. Most of the depiction of the attitude indicator
now is represented on the glass screen, but the information is the same.
The Human ADHRS
Lets look at perception through the
eyes of a pilot. The visual reference that determine our place in space is
based on distance, speed and depth of objects. The comparative size of similar
objects determines distance. The change in the texture and contrast between two
objects also define distance. Relative velocity of objects at different
distances are different, thereby determining speed. Looking through the window
of a moving train the closer trees whoosh by while the trees at a distance move
slowly across the landscape. The clarity and blurriness of objects gives us the
depth perception. All these perceived differences reside with the eyes and the
brain interprets accordingly. Loss of the surrounding landscape can limit that
focus and so trouble begins.
Night flights in VFR conditions can
be disconcerting to a pilot too. It is important to use peripheral vision for
gathering information from the landscape. Focusing on an object directly will
limit information since the cones (structured for bright light and acuity) are
centered and the rods (designed for lower ambient light and greater recruitment
for stimulation) are aggregated around the center. The rods react to low
intensity light and their function is wiped out for 30-40minutes after exposure
to bright light at night while the cones function well during the day and their
recovery time is 3-5 minutes after exposure. So when the sun is spanning the
other side of midnight, focusing on objects is not a good practice. For one, it
can create a jumbled sense of understanding. It can create false movement. This
is called Autokinesis, an event that can occur in the dark when a lighted
object is focused upon on a dark moonless night – the object appears to move on
its own volition. It is therefore important to scan the environment in sectors
periodically for total landscape visualization and orientation. My personal
belief is to fly instruments at night all the time no matter what the
meteorological condition. Oh and by the way if someone ahead of you on the
taxiway has his/her strobes on use your deepest airline voice and tell him,
“Kill those strobes”. That goes for everyone.
What then operates when the eyes
don’t have it. There are two other senses that help/hinder. The two systems
that give us some back up are the vestibular system and the kinesthetic
sensorium. The former is a resident in the middle ear and resides in a space a
lot smaller then the ADHRS in the black boxes in the airplane. The vestibular
system comprises of a contained space collocated as three semicircular canals
mated together to the same cavity- the Utricle. These canals are natural
gyroscopes located in three orthogonal planes depicted on (figure 1) and they
align us for pitch, yaw and roll motion. Within the Utricle and the canals is a
fluid called endolymph and mixed into this fluid are little sand-like particles
called otoconia. Resident in the walls of the Utricle are hair-like
projections. As we move the fluid moves within the canal and the otoconia rest
on the hair cells, which bends and defines positional awareness, (Figure 2).
The minimal detection rate by the vestibular system is 1.5 degrees per second.
Once the movement continues in the same direction for a period of time The fluid movement stabilizes, the hair
straighten and the sensation of movement ceases. It is the deformation of the
hair cell imposed upon it by the angular force vector of movement that
determines the velocity. Once the force is continuous in the same plane the
hair cells relax and the perception of movement is lost. Thus the rate of
change defines the position rather than the change itself. This is called the
“washback motion” effect where magnitude of motion falls below the threshold of
perception. That is the problem in flight. If you close your eyes and the CFI
in the right seat puts the plane in a coordinated 10-20 bank doing a 360
degrees turn, the turning sensation will cease and you will feel that you are
straight and level. Or if he/she changes the bank angle from 45 degrees to 30
degrees the student pilot will sense straight and level again. This very
sensation then causes faulty inputs in times of distress to a VFR and a
non-proficient IFR rated pilot.
The Kinesthetic sensorium is
located in the skin and the joints. The baro-receptors in the joints give us
the tale of the tape related to g-forces, hence the “flying by the seat of the
pants”. A CFI does not have to see the attitude indicator nor the VSI to see
the student is doing poorly on 45 degrees banked 360 degrees turn. He “feels”
it!
Conclusions drawn from above lead
anyone including pilots with one and only one determination:
1.
If you are a VFR only pilot get an IFR rating and fly in
actual conditions with an instructor to get comfortable.
2.
If you are IFR rated then fly in the actual condition with an
instructor till you have achieved comfort level.
3.
Flight at night should be considered an instrument flight.
Reliance on the eyes in the cockpit on reliable instruments is a gateway to
safe flight.
Let me change hats and discuss the rationale for
cerebral (brain) safety. By that I mean the cognitive efforts of understanding
the information gathered is interpreted by the brain. If the brain is under
duress from any sets of circumstances then the interpretive imaging by the
brain will falter and alter the perceived data. Studies done by using the BOLD
method (Blood oxygen level dependent) fMRI (functional Magnetic Resonance
Imaging) revealed that there is a definite reduction in the functional cortical
mass given a depressive influence. These influences include: Fatigue or lack of
Rest, Alcohol, Sedatives, and Tranquilizers, Some Over The Counter medications
and Emotions. It is therefore imperative to have fully functional vault of tricks
up your cortex prior to a flight. There are many things that will make you go
bump in the night. Limit them to zero and live to fly another day.
Here
are a few rules to live long by:
1.
Don’t drink and fly
2.
Don’t take medications and fly – unless you are past three
times the dosing of the medication. If the medication is to be given every six
hours then delay flight 18 hours after the last dose
3.
Get plenty of Rest
4.
Get plenty of daily exercise and don’t smoke – nicotine is a
drug!
5.
Drink fluids – dehydration makes for sluggish blood flow and
contraction of the blood supply.
6.
Check you emotions at the cockpit door – if you cant wait till
the cause of that emotion is past.
7.
Don’t fly with a cold – blocks the Eustachian tubes to the
middle ear, makes one susceptible to false sensory input and ear aches – as
babies in the commercial flight will attest to.
8.
Always have a plan A and a plan B – and execute them in
sequence as needed.
9.
Get an IFR rating if you don’t have it and even if you don’t
intend to fly IFR.
10.
Verify and Trust your instruments.
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