Cognition in Aviation — Page 199, Lesson 317

Let’s start with a sobering reality. However conscientiously you maintain a lookout, it is probably true that detection of all possible collision risks cannot be guaranteed with purely visual scanning. In an experiment in the USA with aircraft flying in good VMC conditions — that is, good visual meteorological conditions — pilots were warned of aircraft on collision headings from ahead. Even with almost perfect visibility, and with prewarning, only 50% of the pilots were able to detect the approaching aircraft in sufficient time that would have enabled them to take avoiding action. So half the pilots missed it, even though they knew something was coming. That tells you how serious the visual detection problem is. Let me summarise the two problems you face as a pilot in recognising immediate danger from a collision threat. First, retinal size. As the aircraft presenting the hazard approaches, its retinal size increases. The rate of that increase has been plotted in Figure 10.11 for an aircraft with a closing speed of 800 knots. What you need to know is that the image remains very small until very shortly before impact. So even though the threat is coming straight at you, your eye doesn't get a big, obvious image until it is almost too late. Second, LCB — that stands for line of constant bearing. If the conflicting aircraft remains on a constant relative bearing, danger is at a maximum because there will be no movement cue aiding detection. In plain terms, if the other aircraft stays at the same angle relative to your aircraft, it doesn't appear to move across your field of view — it just gets bigger, and your brain gets no motion signal to alert you. The situation is worsened if the other aircraft is positioned, from the pilot’s perspective of view, behind a windscreen support or in your blind spot. Now let’s talk about saccade. There are problems associated with the way the eye moves and how it takes in information. Unless you are following a moving object, the eye does not move smoothly but in a series of jerks. Each movement is known as a saccade, and it is followed by a rest period when the eye samples its new field. Smooth vision is achieved by the visual cortex of the brain so that the observer is never conscious of the saccade. You don't feel the jerks — your brain fills in the gaps. The average saccade and rest period takes about one third of a second. Because the area within which we have good visual acuity is small, it means that eye movements must be frequent and small, and the rest periods of short duration to ensure that the sky is covered. You can't just sweep your eyes smoothly across the sky and expect to see everything. So what is the recommended scanning technique? Here are the key points. Each movement should be of 10° at the most, and each area should be observed for at least 2 seconds to allow detection. Airspace above and below the aircraft must be covered. And the sky should be covered in overlapping sectors of about 10°. That way you systematically cover the entire visual field with small, deliberate steps, giving your eye time to actually register what is there.