2.C : Visual Scanning and Collision Avoidance

The pilot is obligated to remain constantly alert to all traffic movement within the field of vision, as well as periodically scanning the entire visual field to detect conflicting aircraft.

During one glance only a very small area (called the fovea) has the ability to send a clear sharply focused image to the brain. (This is during daylight, nighttime works differently.) All other visual info not processed directly through the fovea will be less detailed. Therefore, to scan effectively you use short regularly spaced eye movements bringing successive areas of the sky into the central visual field. Each movement should not exceed 10 degrees, and should be observed for at least one second. Peripheral vision can be useful in spotting collision threats, since apparent movement is often detected by the peripherals.

Visual search at night depends almost entirely on the peripherals. The fovea is great in the daytime, but doesn’t see well at night whereas your peripheral vision is much more effective in the dark.

It is often the case that prior to executing some operation you should clear the area into which you will be traveling. Before taxiing onto the runway clear the approach area for traffic, maneuvering if needed to visually inspect the whole area. During climbs and descents engage in slight right/left turning to allow a view of the area ahead. During straight and level flight maintain a regular scan of the visual field for traffic.

Traffic patterns require very methodical clearing, and collision detection is best done by entering the pattern right at pattern altitude, and scanning for traffic at your altitude. Descending into the patten can be extremely hazardous as it can be difficult to spot traffic ahead and below your aircraft.

Similar to traffic patterns (which is where aircraft congregate) scanning for traffic as you transition over a VOR is critical as well. Even in the era of "GPS direct" the airways converge on VOR sites, so vigilance must be maintained there and at airway intersections.

During training operations, when maneuvering, clearing turns must be performed to insure the maneuver can be performed safely. Generally the routine is to do two 90 degree turns, one in each direction, but the goal is to visually scan the entire area into which you will be maneuvering before initiating the maneuver. Each area cleared should be verbally announced (i.e. "Clear left, right, above, and below"). Remain aware of the blind spots in aircraft, and the differences between the blind spots in high wing versus low wing aircraft.

Approaching aircraft can have extremely high closure rates. Studies show that the minimum time that a pilot takes to spot traffic, identify it, realize it is a collision threat, react, and then have the plane respond is at least 12.5 seconds. Thus constant vigilance to identify threats early is essential.

There are areas where heightened vigilance is required, and these are places where aircraft cluster. This would be near airports, in Class B, C, D, airspace and Class E surface areas. Being in a radar environment is no guarantee that all traffic will be called out, so don’t rely solely on ATC for avoidance.

One component of the threat identification is to determine if a target is at your altitude or not. Use the horizon as a reference point, and if the target is above the horizon it is probably on a higher flight path, with the opposite being true if the target is below the horizon. Any target that shows no relative motion with respect to your aircraft is probably on a collision course. If it shows no lateral or vertical motion and simply gets bigger …​. take appropriate action.

If you have some distance, often a simple change of heading to point at the tail of the other aircraft is all that is needed to avoid collision. Be familiar with the Right-of-Way Rules, and follow FARs when able, but ultimately do whatever is required to avoid collision. Anticipate the possibility that the other aircraft may make a sudden maneuver and maintain visual contact until any chance of collision has passed.

There are actions which can be taken by the pilot, in advance, to improve their ability to avoid collisions. Being prepared in advance, using proper preflight planning, can permit more time to actually scan for traffic during flight. The condition of the windshield can also impact the ability to spot traffic, so having a clear/clean windscreen improves visibility.

During flight understanding (and not creating) visual obstructions in the cockpit can improve the ability to identify targets. Don’t put charts or other items where the view is impaired, and maneuver to see around other immovable obstructions during flight.

Finally, use external lights particularly in low-light conditions. Keep interior lights low at night to help maintain night vision, and leverage ATC as a resource whenever possible.

Various conditions can degrade our vision, and many of these are detailed in AIM 8-1-6. Vision is impacted by physical health, and it has been shown that illness, medication, stress, alcohol, fatigue, emotion, hypoxia, and deficiencies in vitamin A and C. Carbon monoxide poisoning, and lack of oxygen can all decrease night vision as well.

Environmental conditions, such as dim illumination and excessive cockpit illumination can impair vision. In dim lighting small print and colors become unreadable. Vision can achieve a degree of dark adaptation where it becomes more sensitive to light if exposed to darkness. It takes at least 30 minutes for full dark adaptation to occur. Since any dark adaptation is lost within moments of being exposed to bright light a pilot should close one eye when using light to preserve some degree of night vision.

Excessive illumination as on a bright sunny day can cause other problems. Light reflected off of the canopy, other surfaces inside the cockpit, clouds, water, and snow can produce glare, squinting and even temporary blindness. Fly with sunglasses or some sort of shading device as much as possible. Other visual problems can be caused by smoke, haze, dust, and flying toward the sun can reduce the ability to see other aircraft.

Finally, a phenomenon called empty field myopia can become a problem when there is little/nothing to see. With nothing to focus on the eyes naturally relax to a focus just in front of the aircraft. This is a form of induced nearsightedness which can cause aircraft at a distance to be overlooked. If recognized, force the eyes to focus further out and maintain the scan for aircraft.

A number of illusions in flight can provoke spatial disorientation. These can only be prevented with reference to reliable, fixed points on the ground, or flight instruments. If you become disoriented trust your instruments! The next few sections discuss various in flight illusions in detail.

There are a handful of illusions that are unique to landing. The prevention is to first anticipate them during approaches, and by carefully inspecting the area around an unfamiliar airport as the pilot gets near. Use available visual aids such as VASI/PAPI and stay proficient with respect to landing procedures.