July 3, 2000 Eye of Experience #29:
Sight, Sound, and Feel |
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Flying an aircraft is a learned skill. As with any skill, we depend on our senses — sight, sound, hearing, touch, and even the sense of smell — to help us perform it. But which of our senses are we using, and when? AVweb's Howard Fried explores how humans use their senses to
July 3, 2000
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| About the Author ... |
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Howard Fried started flying with the Army Air Corps in WWII, where he
served both as a multi-engine instructor pilot and in combat piloting B-17s.
After a stint teaching sociology and on-the-air and management jobs in the
radio business after the war, he turned to teaching flying again full-time.
Over 40,000 general aviation hours later, he is still instructing
and running his own flight school. Along the way he administered over 4,000 flight tests
as a Designated Examiner until victimized by rogue FAA
officials.
He has authored two popular flying books aimed at student pilots and
instructors, Flight Test Tips and Tales and Beyond The Checkride, and a
series of audio tapes, Checkride Tips from
Flying's Eye Of The Examiner.
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previously discussed the subject of flying by "sight picture" as
opposed to "flying by the numbers." Now we will undertake to consider
all the sensory cues that a pilot uses in manipulating the controls of an
airplane and making the machine do what he or she wants it to do (or, at least
keeping it from doing that which he/she doesn't want it to do).
The first of these is, of course, sight. Whether we are VFR or IFR, sight is the
most important of the senses we use in flying. In VFR flying we keep the
airplane upright by noting the position of the wings and nose of the airplane as
they relate to the horizon. We not only control our pitch attitude by sight, but
we judge our angle of bank by sight as well. And when we're IFR it is sight (the
information we get from looking at the instruments) that enables us to remain
upright. We simply must disregard the feeling we get through the inner ear and
rely on what the gages tell us through our eyes. Also, the kinetic feeling we
get from our deep muscles may be entirely wrong as a result of receiving false
information from our inner ears. So much has been written about spatial
disorientation and vertigo that we need not address that subject here. It is
sufficient to note that a false sensation of turning when in fact we are flying
straight can be almost overwhelming. It is at these times that we must force
ourselves to rely on the messages from our instruments received through our eyes
and interpreted by our brains.
We also gather useful information from the sense of sound. Any change in the
engine sound as it drones along through the sky alerts us to a change in our
flight condition. And if it gets really quiet in the cockpit, we know we're in
deep doo-doo. If anybody should ask what a propeller on an airplane is for, tell
'em it's to keep the pilot cool, and if they don't believe you, just watch the
pilot sweat when it stops! Adrenaline really starts flowing when a pilot hears
the engine cough! When the engine skips a beat it really gets our attention. We
immediately start paying a lot more attention to the engine gages. Are the
manifold pressure and tachometer needles steady? Are the oil pressure and
temperature needles in the green? Any unusual sound and we are instantly alert.
The sound of the wind caused by our movement through the air also tells us
things we should know, but not nearly as well as it did in the days of the open-cockpit airplanes, of course. There used to be a saying that as the tone of the
music caused by the wind through the wires grew deeper the pilot didn't need to
worry until he started to hear "Nearer my God to Thee." Then it was
time to bail out. Any major change in the pitch attitude of the airplane will
cause a change in the engine and slipstream noise, and this provides useful data
whether we are VFR or IFR. Of course, the pilot must process the data his senses
send him for it to be useful. But even when we're IFR, a change in the engine
sound may very well be the first clue we get that all is not well. At least it
tells us that something has changed, and nothing we did brought about the
change.
Although pilots are admonished to not trust what they feel when they are in IMC
(instrument meteorological conditions — in cloud), there are some kinds of feel
(sense of touch) which are useful even then. For example, the tension (or lack
of tension) one feels on the controls. Is the yoke getting loose in your hand,
or does it seem to take more than usual pressure on your part to move the yoke?
This kind of feel will alert us to a change in airspeed. In other words, the
pilot must force himself (when in IMC) to ignore what he feels through the seat
of his pants, but should pay close attention to what he feels through the yoke
in his hand. Is it becoming slack, or has an inadvertent increase in speed
required us to exert more pressure to move it? Of course, you really can't tell
anything if you have a death grip on the yoke. You must still strive for a light
touch on all the controls, particularly the yoke and the rudder pedals. If the
airplane is properly trimmed, a very light touch is all it takes to command the
desired response. The old saw about holding the stick as if it was a little
sparrow works in this situation. If you don't have a firm grip, it will fly
away, but if you grip it too hard, you'll kill it.
Now to expand on this business of sight, sound, and feel. With respect to sight,
we've already had a lot to say about the "sight picture" by which we
fly in the VFR environment. We have the whole world at our disposal, a
25,000-mile reference by which we can not only keep the airplane upright, but by
which we can maneuver it and make it comply with our desires. This allows us to
ignore the instrument panel except for the occasional scan to monitor the gages
and see that all is well while we spend our time looking around outside,
enjoying the scenery and keeping the airplane on course by reference to ground
objects, and, obviously looking for traffic, which we can't avoid if we don't
see. Of course seeing alone is not enough. We have to understand what we're
seeing, analyze and interpret the messages we're getting and take appropriate
action. And again, this is true whether we're VFR or IFR. Even when VFR, we use
our sense of sight to monitor the gages that inform us of the state of health
of the engine(s). If the heading or altitude should wander off, it is our sense
of sight that tells us about it, and tells us when we've made just the right
adjustment to correct the situation. In this situation sight is supplemented by
both sound and feel.
Any change in the sound of the drone of the engine(s) will alert us to the fact
that something is happening even sooner than the engine instruments themselves
(manifold pressure gage and tachometer, but not the oil temperature, oil
pressure, and cylinder head temp gages, as well as those instruments that
advise us regarding the health of the electrical system). If the engine skips a
beat we hear it do so long before we see it on the tachometer (unless we happen
to be watching the tach at the instant it happens). If there is a subtle change
in the pitch attitude of the airplane our ears alert us to the fact, and if
we're in good VFR weather, we probably will notice the change in the sound of
the engine before we catch it on the altimeter or the vertical speed indicator.
So it can be seen that the sense of sound (hearing) can be quite important to a
pilot. This sense may also be coupled with feeling to give us even more input.
We "hear" by feeling a change in subtle vibrations.
Given enough experience, we all develop an "educated rear end." In
other words we feel a slip or skid in the seat of the pants without the aid of
the spirit level (the so called ball bank indicator or slip and skid indicator).
Some people are more sensitive than others to this kind of unusual motion. For
example, my wife, who had been exceptionally prone to motion sickness all her
life, could always detect the slightest change in motion, but it took many
thousands of hours of flying before I became as good at it as she always
was. Now, however, if the airplane isn't perfectly balanced, if there's any slip
or skid at all, I can feel it in the seat of my pants. I sometimes wonder at how
some pilots can fly along in a steady slight skid or slip and be totally unaware
of the condition. I've sat in airplanes and sworn that the pilot must be
unconscious not to feel what's happening as the airplane slides sideways through
the sky.
Another kind of sense of feel occurs when we encounter turbulence. After slowing
to maneuvering speed and cinching the belt and harness up tight we sometimes get
a jolt that causes the head to meet the ceiling, and believe me, you feel that
bump! A downdraft resulting in a sudden drop in altitude causes a sensation in
the pit of the stomach similar to what is experienced in the start of a rapid
decent in an elevator, or on the downside of a roller coaster ride. This, too,
is feeling. Conversely, the added force of gravity ("g" load) felt
with an abrupt pull-up or steep turn pushes us down in the seat and we
definitely feel this, too. We know it when we get heavy. Here, too, the controls
tighten up, just as they do with an increase in speed.
In addition to sight, sound, and feel, even the sense of smell enters into the
equation. And although it does not properly belong with sight, sound, and touch
as one of the primary senses we use when flying, still it should be covered
here. How about that faint whiff of electrical fire? Or worse yet, gas or oil
fire?
I had a friend whose passengers got a strong odor of gasoline while flying
at 7,000 feet, but he just kept going (he was only 30-odd miles from home and
returning from a long trip). About then the engine in his Cessna 210 sputtered
and quit. It died of fuel exhaustion, in spite of the fact that he was one of
those guys who kept very careful records of the time in his tanks, rather than
relying on notoriously unreliable fuel gages. He glided to an uneventful landing
on a small, rough, sod private strip, which by happenstance was almost directly
under him when the engine died.
I happened to be overhead at the time and by
chance I was monitoring the frequency, so I landed behind him and flew him and
his two passengers out, but not before we found the belly of his airplane full
of avgas. The fuel line that runs down inside the right door post had sprung a
leak and all the gas (we drained out well in excess of a dozen gallons the next
day) from his right wing tank had descended to the space between the cabin floor
and the bottom skin of the airplane. Any errant spark could have spelled fini to
the airplane and its occupants. Thank goodness none of the people aboard had
decided to smoke on that flight! I later learned that the reason nobody aboard
lit up was because of the strong odor of gasoline.
Usual Boilerplate: If you have a comment regarding this
column, please post it here rather than sending it to me by direct email. That
way others may benefit from your input.
There are two things about which everyone who holds
an airman certificate is deeply concerned, and rightly so. One, the
holder of any pilot certificate is concerned about the possible loss
of his or her medical certificate. Two, all certificate holders are
concerned about the possibility of being hit with a violation,
unknowingly and inadvertently. My third book,
VIOLATION!, addresses
this subject. It may be ordered by emailing me at hfried@avweb.com.
The cover price is $29.95, but AVweb readers may have it for $23.95
plus $4.50 shipping and handling. Order by Visa, Mastercard or
American Express.
— Howard
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