Cognition in Aviation — Page 199, Lesson 319

I want to walk you through a section on cognition in aviation, starting with some vital points about how we use our vision to spot other aircraft, and then moving into special situations where our perception can be fooled by the environment. First, let's talk about peripheral vision. Peripheral vision can be absolutely vital in spotting collision threats. Here's the key mechanism: every time you stop your scan and refocus your eyes, your peripheral vision becomes more important. Why? Because it is through peripheral vision that movement is best detected. This is particularly important by night. In fact, by night it may not even be possible to identify an object by looking directly at it. You may only spot it by looking slightly to one side of the object, thus utilising the rods in your retina and your peripheral vision for detection. So remember, if you're struggling to see something at night, try looking just off to the side of where you expect it to be. Next, a practical technique for the cockpit. It is best to move your body as well as your head to see around physical obstructions in the cockpit — things like doors and windscreen posts. Together, these obstructions can cover a considerable amount of the sky. A small head or body movement may uncover an area that is concealing a threat. Don't just turn your head; shift your whole upper body if you need to. Now, when does this scanning matter most? Particular care must be taken prior to take-off, landing, ascent, or descent. A meticulous scan must be carried out even though you may have received clearance from ATC. Clearance does not mean the sky is clear. And here is a critical rule for collision avoidance: if another aircraft shows no lateral or vertical movement relative to you, but is increasing in size, that means it is on a collision course. Immediate evasion action must be taken. Do not wait. Now let's move into special situations. These are situations mainly caused by environmental factors that mislead our perception. They have resulted in a number of major accidents. Let's look at them one by one. First, rain on the windscreen. There are two separate effects here. The first is refraction. Due to the refraction of raindrops collecting on the cockpit windscreen, the eye sees the runway lower than it actually is. This tends to make the pilot carry out a shallower than normal approach. This is true both by day and by night. The second effect is rain on the windscreen at night. At night, rain on the windscreen can also make runway lights bloom. As a result, the runway appears closer than it really is. Subsequently, the pilot has the impression that the aircraft's closing speed is faster than it is in reality. The pilot may then adjust the approach, resulting in the adoption of a too shallow approach angle. So both effects — the refraction making the runway look lower, and the blooming making it look closer and faster — combine to push you into a shallow approach. That is a dangerous combination. Next, weather. A heavy rain storm between the aircraft and the airfield will make the field seem more distant. So you have the opposite illusion here: the field looks farther away than it really is. Now, water and height judgment. Flying over a smooth water surface makes it extremely difficult to judge height due to the lack of visual cues. This has the effect of the aircraft flying too low — especially over smooth water. There have been a number of instances of helicopters flying into the sea during night approaches onto offshore rigs. Multi-engine aircraft have hit the water with their propellers when attempting to fly at fifty feet over a calm sea or lake. Fifty feet is not a lot of margin, and without visual cues, you can drift down into the water without realising it. Let me show you a diagram that illustrates one of these illusions. This figure shows how the shallower the approach path, the greater the distance between the aiming point and the touchdown point — that's the geometry behind the rain-on-windscreen illusion. And here is another figure that reinforces how these effects combine. It stresses that the result of these two quite different effects combine under the conditions we just discussed. Finally, here is a figure showing the retinal size of an approaching aircraft before impact. This relates to that rule about an aircraft increasing in size with no relative movement — that is the geometry of a collision course. So to summarise: use your peripheral vision, especially at night; move your body to clear obstructions; scan meticulously even with ATC clearance; take immediate action if an aircraft is growing in size with no relative movement; and be aware that rain on the windscreen, weather, and smooth water can all create dangerous illusions that lead to shallow approaches or flying too low.