A Plan to Scan

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Avoiding midairs is predicated upon one important premise: you must look outside the cockpit. Far too often, pilots spend their time with their head inside the cockpit staring at instruments instead of honoring the see and avoid concept. How much time should be spent looking outside and inside the cockpit? Many years ago a military study indicated that on a 17 second cycle, approximately 3 seconds should be spent inside the cockpit with 14 seconds spent looking outside. That's approximately a 1 second inside to 5 second outside ratio. These are good numbers to follow.

Looking outside the cockpit is one thing; knowing how to look, another. Scanning for traffic requires that you understand another peculiarity about the eye: objects are difficult to detect when the eye is in motion. Effective scanning requires the eyes be held still for a very short time to detect objects. Perhaps the best way to scan is to move your eyes in a series of short, regularly spaced movements that bring successive areas of the sky into the central visual field. The FAA suggests that each movement should not exceed 10 degrees with each area being observed for at least 1 second to enable detection.

Since the brain is already trained to process sight information presented from left to right, you will probably find it easier to start your scan from over your left shoulder proceeding to the right across the windshield, as shown in Figure 1.

Whatever you do, don't forget to scan the area behind you. Many years ago an AOPA (Aircraft Owner's and Pilot's Association) study indicated that the majority of midairs occur with one aircraft overtaking another (one study indicated that 82% of the accidents occurred this way). Obviously this is a faster aircraft overtaking a slower one. This becomes a greater concern when you're operating in an area where fast and slow aircraft mix. Scanning the rear quadrants may take some neck bending or turning of the aircraft, depending on the aircraft configuration. Granted, unless you've seen the movie The Exorcist, you may not realize that such neck twisting is possible. Nevertheless, even if your head can't spin on its axis, make gentle turns in the airplane to take a peek at what's behind you.

Another consideration when scanning is to prevent being a victim of empty-field myopia. This condition usually occurs when you're flying above a cloud or haze layer with nothing specific to focus on outside the airplane. This causes the eyes to relax and seek a comfortable focal distance ranging anywhere from 10 to 30 feet. This means you may be looking outside the airplane without actually being able to identify traffic. To overcome this problem you should try to momentarily fix your eyes on a ground object off in the distance (if possible) before commencing your scan.

Excerpted from: Rod Machado's Private Pilot Handbook.

For more information on this subject, see "Collision Avoidance Made Easy" and "See & Avoid."