July 1, 2011
By Rod Machado
Do you know what magic is? It’s pretty simple. It’s the exact opposite of what a (good) teacher does. The teacher provides perceptual information that leads to insights and ultimately ends with you understanding something. The magician, however, prevents you from understanding anything, lest his sleight go over like a pregnant pole vaulter. The magician does this by using misdirection to keep you from seeing what he’s actually doing. If you can’t see what’s happening, it’s hard to understand what’s happened. Let’s call this the magic effect, because it can lead us to believe what we see, when seeing shouldn’t lead to believing.
I’ll bet the last rabbit in my hat that anyone who’s ever driven a car at night has experienced the magic effect to some degree. At night, we can see lighted objects at great distances—in much the same way we see normally illuminated objects during the day. We can’t, however, easily see unlighted objects such as the road, curves, or foreign objects along the periphery of the road. When it’s dark, we’re deprived of vital visual information that keeps us from understanding our speed in relation to the road.
It’s magic, right? Without this information to stimulate our brake gland, we tend to drive faster than is safe. This is one very big reason that 40 percent of the fatal car accidents occur at night, despite there being 60 percent less traffic during that time. Said another way, we’re bringing daytime driving strategies to the road at night, and we’re paying a hefty price for it. It’s as if we’re at a magic show being fooled, and we don’t even know it.
Fly at night, and the magic effect is in full force, especially when the approach environment offers a dark or featureless foreground next to a lighted background. Approaching an isolated desert airport or an airport from over the water at night for example. The dark environment below prevents us from having sufficient visual clues with which to assess our height above the ground. Our natural response is to use what lights we do have to make this assessment. This means using the distant runway edge lighting as well as the environmental lighting around the airport. Using only background lighting clues when approaching from over a dark foreground tricks the mind into thinking the airplane is higher than it is—sometimes, twice as high. If we act on that effect, our response is to descend prematurely or increase our descent rate. The result is often a landing when there’s no airport beneath the airplane, known as CFIT, or controlled flight into terrain. The lack of perceptual information from beneath our airplane lures us downward, as if our machine is being drawn into a black hole. This is known as the black hole illusion, and it’s one of aviation’s most deadly perceptual illusions. Avoiding falling prey to the black hole illusion means avoiding the use of daytime flying strategies when operating an airplane at night. Let’s begin with a common daytime landing strategy that we surely want to avoid at night—the straight-in approach.
Long straight-in approaches at night to runways having no visual or electronic glidepath information provide the perfect setup for the magic effect. A good nighttime strategy for landing is to overfly the airport and enter a normal traffic pattern for landing. You might even gain a tactical advantage by keeping the pattern a bit tighter and using short-field (over an obstacle) landing procedures, even when no obstacle actually exists. Remaining closer to the runway environment means having more perceptual lighting clues with which to assess your height above the ground. Research shows that the black hole illusion tends to become less effective (less illusory) as you move closer to the runway.
Rod Machado will entertain and educate pilots at AOPA Aviation Summit, September 22 through 24, in Hartford, Connecticut.
What happens if you’re making an approach to a runway having a VASI or a WAAS-based advisory glidepath? The answer is simple—use it. But use it based on its stated limitations. For example, most VASIs offer obstacle clearance only when the airplane is within 10 degrees of either side of the runway centerline. Keep in mind that some VASIs are offset from that centerline, to provide a descent path away from local obstacles (read about those things in the Airport/Facility Directory).
Even with VASI (or electronic glidepath) information, the black hole illusion still tempts some pilots to leave the glidepath prematurely, resulting in red and white lights turning green as the light filters through the grass. This is one instance where you don’t want to feel either the magic or the grass beneath your feet. Resist the urge to merge with featureless terrain below you.
In his book Illusions, Richard Bach wrote that when you know what the magician knows, it’s not magic anymore. The magic works only as long as the magician can limit what we see. A dark environment often accomplishes the same thing for pilots, leading us to a big misunderstanding of our airplane’s proximity to the ground.
That’s why it’s important to understand how the black hole illusion works. It’s one instance where seeing the lights does not mean that we’ve “seen the light.”
Rod Machado is a CFI and aviation speaker with more than 8,000 flight hours. Visit the author’s blog.
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