Cognition in Aviation — Page 199, Lesson 321

I want to walk you through a set of visual illusions and spatial orientation factors that directly affect how you judge height, distance, and approach path when flying. These are not just interesting facts — they are real hazards that have caused accidents, and understanding them is part of your professional training. Let's start with snow coverage. Snow does more than just make the ground look white. It leads to false height judgements, and it often makes it difficult to decide where the surface ends and the sky begins. That happens because snow removes the normal visual and focal clues your eyes rely on to pick out the horizon or the ground contour. It is easy to mistake snow-covered mountains for clouds, and that has produced catastrophic results — pilots have flown into terrain thinking it was a cloud. There are two distinct causes of what we call whiteout. The first is blowing snow, where visibility is reduced to zero — even taxiing becomes impossible. The second cause is extended exposure to the reflected glare of snow. That second cause can be most alarming because it manifests itself in the inability to distinguish ground features. The landscape appears to be a flat, smooth plane of white, and accurate height assessment is rendered impossible. There is an added danger: snow may not reflect radar pulses, so high ground will not appear on the weather radar screen. You cannot rely on your radar to warn you of snow-covered terrain. Now let's move to fog, haze, pollution, and low visibility. As a result of fog, haze, or pollution, runway lights appear dim. That dimness gives you the impression that the runway is further away than it actually is. When you think the runway is further away, your natural reaction is to fly a steeper approach than normal to try to reach it. So the illusion drives you toward a steeper, potentially unstable approach path. Runway lights themselves — their intensity — will also lead to errors. The brightness or dimness of the lights will either give the false impression of the runway being closer or more distant than it is. If the lights are brighter than expected, you may think the runway is closer, and you might fly a shallower approach. If they are dimmer, you think it is further away and fly steeper. Either way, incorrect approach angles and incorrect judgement of closing speeds are likely outcomes. Now I want to introduce a fundamental concept: spatial orientation in flight and what is called "seat-of-the-pants" flying. As we saw in Chapter 4, the vestibular apparatus — that is the balance organ in your inner ear — detects the orientation and movements only of the head. That is a critical limitation. It does not tell you where your body is relative to the aircraft or where your limbs are relative to each other. So the nervous centres in your brain also need information depicting the spatial orientation of the head with respect to the body, as well as the spatial orientation of the different parts of the body with respect to each other. That information is transmitted by the proprioceptors. Proprioceptors are components of the nervous system located under the skin — subcutaneous — in the neck and the major parts of the body. They sense the position and movement of your body parts. A pilot who relies on these inputs — the feel of the seat, the pressure on the back, the sense of being pushed down or lifted — is sometimes referred to as flying by the "seat-of-the-pants". That phrase is not just a casual expression; it describes a real reliance on proprioceptive cues. But here is the most important point: the most important sense with regards to spatial orientation is sight. Even without the inputs from the vestibular apparatus — even if your inner ear were not working — a person can still use his or her visual images of the outside world to maintain spatial orientation. Vision dominates. That is why visual illusions like the ones we just discussed — snow whiteout, dim lights in fog, bright or dim runway lights — are so dangerous. They attack your primary orientation sense.