Cognition in Aviation — Page 193, Lesson 308

I want to walk you through a set of visual illusions that can affect your approach and landing judgment — specifically illusions caused by sloping terrain, sloping runways, and runway width. These are all part of cognition in aviation, because your brain is interpreting visual cues, and if those cues are misleading, your perception of height, distance, and slope can be wrong. Let's start with sloping ground. If you're approaching an airfield that sits on sloping terrain, or the runway itself is sloping, your brain uses the terrain to estimate where the horizon is. If that estimate is incorrect, you'll make an incorrect judgment about your approach slope. The excerpt also says the length of a sloping runway may be misjudged. So the slope distorts both your sense of the horizon and your sense of how long the runway is. Now let's look at upsloping runways — that means the runway rises as it goes away from you, so the far end is higher than the threshold. In this case, the visual cues at the threshold encourage you to descend. That leads to an approach that tends to be too low. If you continue that low approach, your wheels will contact the runway farther behind your visual aiming point than normal, and there's a possibility of touching down in the undershoot area — that is, short of the runway pavement. Additionally, an upsloping runway will appear shorter than it actually is. It looks closer, which creates a mistaken belief that you need to descend sooner. Now the opposite: downsloping runways. Here the runway slopes downward away from you, so the far end is lower than the threshold. The visual cues at the threshold encourage you to climb. That leads to an approach that tends to be too high. If you're too high, you may land further into the runway than planned, which reduces the runway distance available for landing and braking. A downsloping runway will appear longer than it actually is — it looks farther away, which creates a mistaken belief that you don't need to descend yet. The excerpt references Figure 10.6 for these sloping runway effects, and you can see that figure on screen. Now let's talk about width of runways. The width of the runway can cause incorrect height judgments on final approach. If you're a pilot used to a standard width runway of 150 feet — that's 46 metres — and you approach an unfamiliar airfield with a narrower runway, you'll tend to judge that you are too high, and therefore you'll round out — that's the flare — on too low an approach. Conversely, at an airfield with a wider runway than you're used to, the tendency is to round out too high on the approach, because you're trying to match the visual scene to your expectation. The excerpt gives a specific real-world example. Students from Kidlington are accustomed to a narrow runway width of 75 feet — that's 23 metres. When they land for the first time at Filton, where the runway width is 300 feet — 92 metres — they tend to flare much too high on that first landing. So the visual cue of runway width is powerful enough to override your actual height perception. To summarise: sloping terrain and sloping runways distort your horizon estimate and your sense of runway length, pushing you either low or high. Runway width distorts your height perception, pushing you to flare too low on a narrow runway or too high on a wide one. These are all illusions you need to be aware of as a pilot, because your brain will naturally follow the misleading visual cues unless you consciously cross-check with your instruments.