Visual Scanning Techniques

The eye is the primary means of identifying what is happening around us, as 80% of our information intake is conducted through the eyes. During flight we depend on our eyes to provide basic input necessary for flying, such as proximity to other air traffic, direction and speed. A basic understanding of the eyes’ limitations in target detection is important for avoiding collisions.

Vision is influenced by atmospheric conditions, glare, lighting, temperature, aircraft design, and so forth. On a sunny day, for example, glare is worse. Glare makes it hard to see what is at a distance as well as making the scanning process uncomfortable.

Vision can be affected by different levels of illumination:

1. Bright illumination: reflected off of clouds, water, snow, and desert terrain; produces glare resulting in eye strain.
2. Dark Adaptation: Eyes must have at least 20 to 30 minutes to adjust to reduced light conditions. Red light helps night vision, however, it distorts colour and makes details hard to perceive.
3. Light adaptation can be destroyed in seconds, though closing one eye may preserve some.

Additionally, vision is impaired by exposure to altitudes above 5,000 feet ASL, carbon monoxide inhaled from smoking and exhaust fumes, a deficiency of Vitamin A in one’s diet, and prolonged exposure to bright sunlight.

One significant limitation of the eye is the time required for accommodation, or refocusing of objects both near and far. It takes 1 to 2 seconds for the eyes to adjust during refocusing. Considering that you may need up 10 seconds to spot aircraft traffic, identify it, and take action to avoid a mid-air collision, each second is critical. Looking at an empty area of the sky causes empty field myopia and will impair your ability to focus. You should look at a cloud patch or tree line to allow your eyes to focus.

Another eye limitation is the narrow field of vision. While the eyes can observe an approximate 200-degree arc of the horizon at one glance, only a very small centre area called the fovea, in the rear of the eye, has the ability to send clear, sharply focused messages to the brain. All other visual information that is not processed directly through the fovea will be less detailed.

The retina of the eye is more sensitive to hypoxia than any part of the body. One of the first symptoms of hypoxia is a decrease in night vision. For this reason, pilots flying at night are advised to use oxygen, if available.

Many factors affect vision. Hypoxia, carbon monoxide poisoning, alcohol, drugs, fatigue and smoking are only a few of these. After time spent in bright sunlight, the eye is slow to adapt to darkness and this may reduce night vision. To improve dark adaption, pilots should use sunglasses during the day to avoid eye fatigue. At night, cockpit lights should be kept low to maintain the dark adaption needed to see clearly outside the cockpit.

Despite modern electronics, pilots still fly in a “see-and-be seen” world. For best results, good vision is only one of the requirements. In the cockpit, it must be reinforced with good visual scan practices, especially at night. Such practices are an acquired, not an inherent, skill. In performing a visual scan, the eyes should be focused at a range that will ensure detection of traffic while there is still time to take avoiding action. This requires that pilots take an object on the horizon, focus on it and then scan all sectors of the sky, refocusing as needed to avoid “empty-field myopia” (empty-sky myopia), which can result from gazing at a featureless landscape or cloudscape. Conscientious scanning of all sections of the sky, interspersed with brief interludes of focusing on distant objects, will improve a pilot’s ability to detect distant aircraft. A clean canopy is also essential, particularly with bright sunlight. Spots on the windshield easily lead to dazzle glare and can interfere with long-range focus.

The same scan is required at night, with one difference: the part of the eye that is best suited for night vision is not in the centre. An object detected in barely adequate light will disappear if viewed directly, but will often reappear if one looks 10 to 15° to one side of the object.

Avoiding collisions requires effective scanning from before takeoff until the aircraft comes to a stop at the end of a flight. The best way to avoid collisions is by learning how to use your eyes for efficient scanning, as well as understanding the visual limitations described above and not overestimating your visual abilities.

Before takeoff, visually scan the airspace around your intended take-off location. Assess traffic audibly as well, listening for engine sounds and, if possible, radio transmissions. After takeoff, keep scanning throughout the flight to ensure that no other traffic will be a hazard to your aircraft.

Movement can be detected more effectively through peripheral vision, so this pause in a visual scan allows for easier detection of threats such as aircraft and birds. An effective scan is a continuous process used by the pilot and observer to cover all areas of the sky visible from the control station.

Although horizontal back-and-forth eye movements seem to be preferred by most pilots, every pilot should develop a scanning pattern that is most comfortable for them and then adhere to it to assure optimum scanning. Pilots should realize that their eyes may require several seconds to refocus when switching views between items in or on the control station and distant objects. The eyes will also tire more quickly when forced to adjust to distances immediately after close-up focus, as required for scanning the control station. While there is no “one size fits all” technique for an optimum scan, many pilots use some form of the “block” system scan. This scan involves dividing the sky into blocks, each spanning approximately 10 to 15 degrees of the horizon and 10 to 15 degrees above it. Imagine a point in space at the centre of each block. Focus on each point to allow the eye to detecta conflict within the foveal field, as well as objects in the peripheral area around the centre of each scanning block.

Good scanning requires constant attention-sharing with other piloting tasks, and pilots should remember that good scanning is easily degraded by conditions such as boredom, illness, fatigue, preoccupation with other tasks or ideas, and anxiety.