Eye of Experience #29:
Sight, Sound, and Feel
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
We 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.
All Together Now
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.
Seat Of The Pants ...
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.
... And One Other Sense
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.
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