While compensation is a necessary piloting skill, the fact that you have to do it means your workload has increased. Leaning to reach a switch or see an instrument is always a distraction. These minor distractions generally go unnoticed at altitude on a clear day, but they can be significant during high workload flying such as actual instrument approaches or during emergencies.
Mentally climb into the left seat of your airplane and visualize your physical movements as we explore a few PAI issues.
Location
Switches, levers, knobs, handles, and instruments are located throughout the cockpit. The more sophisticated the airplane, the more of these gadgets you'll find. Often they are squeezed into the same space as a less complex airplane. Limited "optimum" space - the location where these devices can best be seen and reached - forces manufacturers to place some controls and instruments in less than optimum locations.
Ever fly an airplane where the yoke obstructs your view of something on the lower instrument panel? Moving the yoke out of the way during flight is generally not an option, so you move your head or lean to see around the yoke. The same can be true for reading a gauge that's partially blocked by a protruding radio stack or engine control levers in their high-power position.
Before you fly an airplane, you should sit in the cockpit, look around, and ask yourself some questions. What instruments or switches are blocked by something that obstructs your view of them? Are they important? Are they among those you want to refer to frequently, such as navigation instruments? Could your blocked view of them keep you from noticing a deteriorating condition that could have significant consequences such as cabin pressure or oil pressure?
Notice which devices are blocked from view and assess the consequence of their going unnoticed. Do you deal with this annoyance from a convenience standpoint (don't check it as often as you should) or a compensation standpoint (incorporate a lean and look task into your instrument scan)?
Physiology experts say rapid head motions can encourage vertigo during instrument flight. Think about how quickly you move your head to get a quick peek at an obstructed gauge.
You might be able to easily see gauges located on the right side of the instrument panel, but you might still have to compensate to read them. If the instrument has a recessed face, its bezel may obstruct the markings along the left side of the face. An indicator needle pointing to that region forces you to lean to your right to read it accurately. You can forego the lean as long as this region is within the normal operating range, but if minimum or maximum limits are marked there you'll be more inclined to keep a close eye on the gauge. That means frequent leaning and longer distractions from other piloting tasks.
Parallax is another possibility with analog gauges. These gauges are designed for you to read them head-on, or perpendicular, to their faces. Because the indicator needle is a small distance away from the instrument face, it can appear to indicate a different value if you view it at an angle.
Let's say you're in the left seat trying to read a gauge on the right side of the instrument panel. The closer the needle is to the 12 o'clock position, the higher its reading will appear to be because of parallax error. If the needle were pointing exactly at 12:00, as you view it head-on, it appears to point somewhere between the 12:00 and 1:00 position when you view it from the left. At the 6:00 position the needle appears to point between 5:00 and 6:00 if you view it from the left. The parallax error is minimized when the needle points close to the 3:00 and 9:00 positions. If you hold an analog clock in the position it would be on the panel at arm's length to your right, you can see this parallax effect easily.
Just because you can see all the handles and switches doesn't automatically guarantee you can reach them. Do any switches, levers, handles, or knobs fall into this category in your airplane? Make sure you check them with your lap and shoulder straps tight. Are any of these unreachables part of a checklist you perform at a moment when loosening your shoulder straps is not possible, such as right after takeoff or just prior to landing?
Your reach is not an absolute number when it comes to operating cockpit devices. You can throw a rocker switch with a finger tip at the very end of your outstretched arm. A lever-lock switch requires you to grab it and pull it over a safety notch, however. You won't be able to actuate this kind of switch if you can just reach it with your finger tip - you'll need about two more inches.
Do the switches, handles, and other moveable controls move in the sensible direction? Up for on; down for off; middle for stop? Do you have any switches that are normally "on" during flight and that reside adjacent to those that are normally "off?" Would you rather have all switches point in the same direction for normal operation regardless whether some of the switches will be "on" and others "off?" Different airplanes may have different switchology. So, you must be extra vigilant if you fly more than one airplane.
We generally like controls to move in logical or, at least, traditional directions. How many times have you turned the crank on the ceiling the wrong way while trying to adjust the pitch trim?
Handles and levers should require enough operating force to preclude actuating them inadvertently or giving you a tendency to over-actuate, but they should have a force low enough for easy one-hand operation. Some mechanical flap levers take a notoriously high force to pull to that third notch. Some handles have perfectly acceptable forces, but their location or operation is so awkward that a conscious, concentrated effort is necessary.
Electric flaps are not immune to PAI problems. A spring-loaded switch requires you to hold the switch until the flaps reach the desired deflection. Could you be using that hand for something else? On others you only have to hold the switch while you lower the flaps, but a single flick brings the flaps all the way up. Partially raising these flaps requires two conscious movements. Think about instances where you might want to nurse the flaps up, such as during a go-around. Would you rather have that hand somewhere else during this maneuver?
Guarded switches are guarded for a reason. This passive message forces you to be sure you want to throw this switch. The result is that you make two conscious movements to operate a guarded switch.
Where is the fuel selector in your airplane? Can you reach it with your straps tight? Is it hard to turn? Is it obvious which way you turn it? Can you feel it click into place when you turn it to another tank or to the off position - or do you just sort of point it at the index? Is it on the floor or against a wall where you have to take a foot off the rudder pedal to reach it? If you are flying a twin can you afford to remove your foot from that pedal following an engine failure?
Proximity
One proximity issue is switches with a similiar shape that operate alike and are located adjacent to each other. This arrangement makes it easier to throw the wrong switch inadvertently. There have been cases of pilots who visually identified the proper switch, then looked elsewhere and hit the wrong one. You can see the problem it could create if you reached for the anti-ice switch and turned on the landing light instead.
Having a row of identical switches makes for a pretty instrument panel, but this layout can invite switch selection mistakes.
Congestion is another proximity issue. Are switches and handles so close to another device that actuating one is difficult without also moving the other? Is a handle located between the seats, where grasping it means a blind reach of a beefy arm into a narrow gap? If an emergency procedure requires you to pull a circuit breaker, can you find it quickly? in the dark? Can you pull it out? What breakers are next to it? What would the consequence be if you were to pull one of those by mistake? Study the circuit break panel and figure it out.
Emergency procedures often involve actuating several devices. How many times must you change hands on the yoke to accomplish the corrective measures? The same question is valid for any procedure, from post-takeoff checklists to instrument approaches.
Flying is a multi-sensory event. We rely primarily on vision, but there's no denying the significant influence of sound, feel, and even smell. Stall warning horns are designed to get our attention no matter where we're looking or what we're doing. Is that stall warning horn loud enough for you to hear it while you're approaching a full-power departure stall? If your airplane has warning lights, are they located in your primary field of view?
Tactile cueing is often used to help ensure your hand is on the correct device. For adjacent switch placement, a rocker switch for the landing light and toggle switch for the anti-ice might be a better idea than two rockers. It is no coincidence that landing gear handles are circular and flap switches are flat, or that throttle, mixture, and propeller knobs have different shapes and colors.
You can see a lot of overlap among these arbitrary PAI categories. Location affects seeing, reading, identifying, reaching, and operating a device. Shape, proximity, force needed, and other factors all affect how much of your attention you must devote to operating a device - which is attention you cannot devote to other flying tasks.
Now that you've considered these PAI issues while reading this in your favorite comfy chair, head to the airport. Bring the magazine along. Sit in your parked airplane and physically assess the PAI. Flip switches, operate handles, turn knobs if it is safe to do so. Do it without looking. Simulate emergencies and pay attention to how PAI can cause one task to affect another. Chances are you'll treat a few of those routine tasks with more diligence in the future. Let us know what you find.
For a real eye-opener, perform your PAI evaluation in an unfamiliar airplane. These will be your initial impressions before you've had time to compensate for them automatically. Often the first look is the most revealing.
These PAI issues are just a few of the many out there. We haven't even mentioned the seat/pedals/yoke/throttle relationships. Don't stop looking for PAI problems. You probably won't have much control over the PAI, especially with rental aircraft. You can, however, identify potential PAI problem areas and take extra care while operating those controls.
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