Cognition in Aviation — Page 193, Lesson 303

I want to walk you through a section on cockpit height and the illusions that can affect a pilot during take-off and in the cruise. Let’s start with something that might seem simple but has real consequences: cockpit height above the ground. Your eye height from the ground can be a source of misjudged speed. If you convert from a smaller aircraft to a much larger one—say, from a DC9 where your eye is about 3.48 metres above the ground, to a 747 where your eye is 8.66 metres above the ground—your normal visual references are now at a greater distance. That greater distance gives you the illusion of slower relative motion. So in the initial stages of training on that new type, you may well taxi at excessive speeds without realising it, because everything looks like it's moving more slowly than it actually is. Now let’s move to illusions on take-off, and the first one I want to cover is the somatogravic illusion. In commercial flying, the major accelerations in the longitudinal and rotational planes occur during take-off and go-around. When you accelerate, your brain resolves two forces—weight, which acts vertically downwards, and the acceleration itself—into a single resultant force. That gives you an impression that the nose of the aircraft is pitching up. This encourages you to push the stick forward, and the resultant danger is that you fly into the ground. The effect is particularly dangerous because it's exacerbated by information supplied by the otoliths of the inner ear. The otoliths are part of your vestibular system that detect linear acceleration and gravity, and they feed into this false sensation. Next, let’s look at outside references—specifically, vectional false horizons. These are false impressions that come from visual cues outside the cockpit. The book gives several examples. Immediately after take-off, a false horizon may be perceived when surface lights are confused with stars. Over water, the lights of fishing boats have been mistaken for stars, and the flight path adjusted inappropriately. In hilly terrain, emerging from low cloud or mist on take-off, lights on the ground can be mistaken for stars, leading you to adjust the flight path to a lower and dangerous profile. Gently sloping terrain can create an illusion at any time when flying visually at low level. A bank of sloping cloud across the horizon will give the impression of a wing low—you can see an example of this in the figure on page 194. Also, after take-off or on approach, if the ground slopes down, an illusion of excessive height may be created, and vice versa—if the ground slopes up, you might think you're lower than you are. Now let’s move to illusions in the cruise, and specifically autokinesis. Autokinesis occurs when you stare at an isolated and stationary light while other visual references are inadequate or absent. That staring can cause autokinetic movements of the eyes, giving you the illusion that the light is moving. This can lead you to believe that a single star is another aircraft. Numerous cases have been reported of mistaken identity of lights. The illusion is created by small movements of the eye that the brain ignores and then interprets as motion of the object. The way to avoid it is simple: shift your gaze to eliminate staring. Don't fixate on a single point of light.