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Aviation Learning Center Document How to Avoid a Mid Air Collision - P-8740-51
Author: Federal Aviation Administration Date: Unknown
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Scan Patterns
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Block System

Your best defense against in-flight collisions is an efficient scan pattern. Two basic scans that have proved best for most pilots are variations on a technique called the "block" system. This type of scan is based on the theory that traffic detection can be made only through a series of eye fixations at different points in space. Each of these fixes becomes the focal point of your field of vision (a block 10-15° wide). By fixating every 10-15 degrees wide), you should be able to detect any contrasting or moving object in each block. This gives you 9-12 "blocks" in your scan area, each requiring a minimum of one to two seconds for accommodation and detection.

Side-to-Side Block Scan

One method of block scan is the "side-to-side" motion. Start at the far left of your visual area and make a methodical sweep to the right, pausing in each block to focus. At the end of the scan, return to the panel.

Front-to-Side Block Scan

The second form is the "front-to-side" version. Start with a fixation in the center block of your visual field (approximately the center of the front windshield in front of the pilot). Move your eyes to the left, focusing in each block, swing quickly back to the center block, and repeat the performance to the right (figure 2).

Figure 2

There are other methods of scanning of course, some of which may be as effective for you as the two preceding types. Unless some series of fixations is made, however, there is little likelihood that you will be able to detect all targets in your scan area. When the head is in motion, vision is blurred and the mind will not register targets as such.

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