AOPA Pilot Magazine - March 2021 - 99

P&E

ON INSTRUMENTS

Don't get fooled
Tricked by your senses
BY THOMAS A. HORNE

LEIGH CAULFIELD

SOMEONE ONCE WROTE THAT FLYING ON

instruments was " an unnatural act, punishable by God. " Although this quip was no
doubt intended as a joke, we all know that
flying in actual instrument meteorological
conditions can carry some serious risks.
There's the risk of making technique and
procedural errors, poor decision making,
lapses in judgment, and just plain staying
ahead of the airplane. But there are physiological dangers, too. These can affect all
of us, no matter how many hours and ratings we may have, how often we fly on the
gauges, or the aircraft we fly.
These risks stem from a sort of mindbody disconnect that produces false
illusions, and a variety of other physiological conditions that are often lumped under
the term " spatial disorientation. " They can
crop up any time a pilot is deprived of visual
cues, or whenever the airplane's attitude,
acceleration, or deceleration makes the
inner ear's anatomy trick us into thinking
we're on a flight path or attitude that doesn't

correspond with reality. At its worst, these
inner-ear dynamics can induce vertigo-
that nauseous, spinning sensation that can
cause us to lose control of the airplane.
The ear is a marvelous sensory organ
that gathers sound and sends its impulses
along to the brain for interpretation.
Another function-determining posture
and orientation-is carried out by the inner
ear and is vital for keeping our balance. The
inner ear works great when we're standing,
walking, or carrying out other routine earthbound chores. In flight, it has its limitations.
The inner ear determines our physical
orientation in space by using a system of
three fluid-filled, semicircular canals connected to a series of small chambers lined
with tiny hairs, or cilia. Otoliths-small
crystals-move around with the liquid as
we change our posture or tilt our heads. As
they move, they come in contact with the
cilia, which in turn are connected to nerves
connected to the brain, which uses this
information to help us stay oriented. When

the otoliths move, we get new information.
In flight, where they can move more rapidly,
they give us false information as they slosh
around in those chambers.
Accelerate suddenly, and you can get the
sensation that the airplane is pitching up.
This can cause you to pitch the nose down
to " compensate. " Decelerate, and you'll
think the nose is pitching down, so you're
tempted into pulling up. Quickly level off
from a climb, and you could be in for a crippling bout with a tumbling sensation or feel
like you're going to an inverted attitude.
Other situations involving less
radical maneuvers can cause equally dangerous sensory illusions. Stay in a bank long
enough, and the inner ear's otoliths become
stabilized in their new positions, giving us
the feeling that we're in a level attitude. You
might notice the bank from instrument indications, but to the brain it feels like it just
can't be so. Respond by leveling the wings,
and there's the feeling that you're banking
in the opposite direction. Now there's the
urge to return to the original bank angle,
back where things seemed level. This can
lead to what has been traditionally called
a " graveyard spiral. " If there's a loss of altitude in the banking and rebanking-very
common-then there's the strong temptation to haul back on the yoke to stop it. This
can tighten the bank angle in an escalating
cycle until impact.
Instrument instructors and textbooks
remind students to keep head movements to
a minimum when flying in actual conditions.
There's a good reason: tilting your head
while in a bank can induce vertigo. That's
because the inner ear's fluid and otoliths
are moving simultaneously and in different
planes (the semicircular canals are oriented
in three different angles). The upshot can be
a combination of sensations that make you
feel like you're rolling and pitching at the
same time. Obviously, this leaves the pilot
unable to maintain controlled flight.
The eyes can also play mischief with
the senses. On final approach to a long or
narrow runway, it can appear as though
you're too high, tempting you to dive for the
threshold. On an approach to a wide runway, or one with a downslope, you can get
the feeling you're too low. This creates an
urge to raise the nose. One illusion can give
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AOPA Pilot Magazine - March 2021

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