Image: City of Greeley, Flickr Creative Commons
If all runways were created equal, we would all have a greatly improved chance of making perfect landings every time. There is much to be admired about the pilot who appears to nail a ‘greaser’ no matter the size, terrain or slope of the runway, however, it is likely that our pilot is not just good at landing an aeroplane, but has a keen sense for identifying the illusions that some runways and surrounding terrain can present. Knowing what these illusions are can really help you improve your approaches, which in turn, could turn that awkward thumpy, bumpy landing into a really pro (and safe) one.
Runway width can be the cause of confusion, especially if it is different to what you are accustomed to your home field. For example, a narrow runway will appear as though it is quite some distance away – in other words, your altitude appears too high because the runway looks small. The result is a low approach, followed by a late round out, and possibly landing short or hitting obstacles. On the other hand, your first experience on a runway which is much wider, will get you thinking that you are much closer than you really are, which could lead to a higher approach, pre-mature round out and a ‘firm’ landing. So what can you do about it, especially if you are approaching a field that is new to you, and the runway has a width that is unusual to you? Firstly, the picture is not going to look the same as the runway you usually frequent, so try and check beforehand if you can expect a narrow, or wide runway. This way you can anticipate the illusion that will cause you to round out early or late. A handy tip would be to aim for the height of the windsock, or the top of the hangars for your round out – regardless of the runway width, these are pretty standard in height.
Runway slope can also produce illusions that can mess with your approaches. An uphill runway is always preferable in the sense that your aeroplane will slow down sooner, and you’ll need a shorter landing distance, however, approaching a runway with a distinct uphill slope can be challenging. An uphill gradient will give you the impression that you are higher up in altitude than you actually are, which means that your approach could be on the low side, as you try and correct for the illusion. Conversely, although downhill runways may not be your first choice, they may be your only choice at certain airfields. A downhill slope will cause you to feel that you are lower than you really are, leading to an over-shoot of your intended landing mark, leaving you with less length to land on.
Terrain surrounding the runway can also influence your perception of height. This is especially true if the terrain is featureless such as the sands of the Namib desert, or an approach over snow or water. Also know as the ‘black hole’ effect, particular to night flying when there are no ground lights from which one can determine the height of the aircraft from the ground. A word of caution is also necessary where snow or desert dunes surrounding the runway may be uneven and significantly higher than the runway – always keep a lookout to the sides of your aircraft, and avoid just fixating on the runway.
Although we have discussed some tactics that you can use against these illusions, it usually all comes down to planning. Have a look at Google earth to try and find images of the runway you intend to land on, as well as your alternates so that you know what to expect. The AIP’s will also provide you with important information regarding runway dimensions and slope. Keeping an eye on your altimeter, and knowing the height of your runway, is probably one of the most certain ways of knowing how much height you need to lose. Most importantly of all, if it doesn’t feel right, you can always go around and try again!
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