Making Runways Loooonger
Tiger Moth

by
Budd Davisson, appeared in Flight Training Magazine

It's not how much runway you use, that makes it short, it's how much you waste that usually counts.

When you hear the term “short runway” what number pops into mind? 2800 feet? 2200? 1800? It doesn’t make any difference because everyone reading this answered the question with a different number. Some may have gone as low as 1200 feet or less. Maybe we have some bush pilots in the audience and they’re laughing at any thing longer than 800 feet. The point is that “short” is a relative term and, all other things being equal, your personal definition is determined primarily by three factors: the length of the runways to which you’ve become accustomed, your flying skill and the type of airplane you’re flying.

Taking the last point first, airplane type, it’s a given that the faster, heavier airplanes are going to need more runway. The kinetic energy that has to be overcome to stop an airplane, is a function of the mass of the airplane and the square of the speed at touchdown. So obviously a Bonanza can’t land as short as a 152. However, exactly how much difference is there? And how much runway is actually needed?

Virtually every POH has a set of charts that show how much ground roll a given airplane needs in given conditions. It is industry standard that unless noted otherwise, these numbers are generated at gross weight, zero wind, and “standard conditions,” or approximately 15 degree centigrade (approximately 58 degree Fahrenheit) at sea level, with moderate, not extreme, braking. A few manufacturers don’t adhere to this standard but most do.

POH figures are best-case figures, generated by a new airplane with a factory test pilot at the controls. However, even though they are optimized numbers, they still give a good guideline for how much runway you’ll need after you’ve touched down. Of course, the actual length of the runway used, assuming clear approaches, will be the ground roll plus a little extra to keep the pucker factor under control plus the amount of runway left behind at touchdown. The question then becomes, “How much runway does an airplane actually need in addition to the required ground roll?”

 Just for grins we got our hands on a POH for a late model Bonanza. It said that the ground roll required at gross was 710 feet. Now, how about a C-152? That came in at 475 feet. We kept checking: a C-172 needs 550 feet of ground roll and a Warrior 575 feet.

Okay so light to heavy, C-152 to Bonanza, we have a range of 475 feet to 710 feet or a difference of only 235 feet, just a little over the average distance between two runway lights. Given the numbers, if you put a C-172’s main gear right on the threshold, in theory you should be able to land it in 550 feet without smoking the tires. Okay, to be realistic let’s add 25% because none of us are professional test pilots, which makes it 687 feet.  Do you land your 172 in under 700 feet? Does anyone do that? Not likely, although there are probably some northcountry pilots who habitually put it right on the threshold and get in that short.

Now let’s go back to the original question: how short do you think is short? Chances are the majority of you picked numbers between 1700 and 2000 feet. There are several reasons for that. First of all, the number of paved, public use airports under 2000 feet is fairly small, so very few pilots fly off of runways that short on a regular basis. The average runway is probably somewhere in the 3,000-3,500 foot range, so, when a pilot who spends all of his time on this longer runway turns final to one only two-thirds that long, it looks ridiculously short by comparison. This fits the first definition factor of a short field: you’re not accustomed to something that size, so your perception is that it’s short whether the airplane thinks it is or not.

Then comes the question of pilot skill and this is muddled by some factors that aren’t necessarily skill-related but are actually habits, not skills. Pilots get in the habit of landing longer than is necessary because their home runways are of normal length and there is no reason to worry about running out of pavement. So, they often think in terms of getting down somewhere in the first half of the runway, although some may land in the first third. However, when a pilot thinks in those terms, it’s a unquantifiable measurement. It’s an approximate length that is unique to that specific runway. Few pilots actually apply a yardstick to their landings. They aren’t thinking, “I touched down about 600 feet past the threshold that time,” Because of this, they don’t actually know how much runway they are either using or how much they left behind.

It’s both useful and educational to keep track of where you touchdown on the runway because that distance is wasted runway and is actually what makes a runway short. To reduce this to actual numbers, you could keep mental track of how far down the runway you touchdown on each landing. Many runways offer an ideal way to measure touchdowns because big white squares are painted at the 1000 foot mark. Plus most runway lights are approximately 200 feet apart. Another good measurement is the distance to each turn-off. If you turn off at such-and-such a taxiway, you know exactly how much runway you used, start-to-finish.

So there is no confusion, you should know that when we start talking about landing short, we’re not talking about using true shortfield techniques. That’s a specific technique that was part of your original training and it can, and should be, used on any runway that feels as if it’s out of your comfort zone. However, we want to discuss landing on normal runways using normal techniques. We want to examine how you normally fly and how it can be modified to make every runway longer.

 Let’s face it, if in theory, a 172 will stop in 687 feet with no wind and at gross, the runway we leave behind is the only thing that makes any runway short. Without even landing on the numbers, a 1000 foot runway with good approaches should be plenty.1000 feet, minus the 687 ground roll says you can touchdown 300 feet down the runway and still get stopped. But, we’re not talking about 1000 foot runways here because the chances are you’ll never see one of those. However, if at the beginning of this discussion you said you felt 1800-2000 feet was short, you’ll see a lot of those unless you restrict yourself to nothing but “normal,” plain vanilla runways. Many of the more interesting airports with the more interesting people and airplanes exist under the 1800-2000 foot mark.

1800-2000 foot runways shouldn’t be looked at as being something unusual that requires an unusual approach unless, of course, you’re in the habit of landing 1000 feet down the runway. In this case, it’s the habit that’s making the runway short, not the actual length of the runway. Even a poorly flown Bonanza won’t find 1800 feet short assuming a minimal amount of runway is left behind and the touchdown is at stall or close to it.

When you start keeping track of your touchdown distances pay attention to the approaches that lead up to those distances. Were you fast, high, low, power-off, dragging it in on power, half flap, full flap, what? If you are habitually touching down at the thousand-foot marks, we need start establishing a cause and effect relationship. A thousand feet is a lot of runway to waste and it’s going to make many runways seem incredibly short.

We need to underscore that we aren’t interested in landing right on the numbers. If your airplane will easily roll to a halt in 700-1000 feet, unless you’re landing on a teeny strip there is little to be gained from flying an edge-of-the-envelop approach that puts you super low just off the end of the runway so you’ll hit the numbers. Although it’s good training to be able to hit the numbers on demand, on most runways, it’s unnecessary and on some it may introduce an unnecessary level of danger. One of the better bush pilot axioms says it best, “It’s far better to roll off the other end at 5 mph than land fifty feet short.

Our goal is to be down solidly and able to get on the brakes at the 1000 foot mark, if we want to. That means you’ll be on the runway at 600-800 feet, so the 700-foot ground roll only puts you at 1500 feet. This kind of flying doesn’t require any form of short field approach. It does however require you fly your airplane the way it is supposed to be flown and apply precision to your touchdowns.

Let’s analyze that last sentence “…require you fly your airplane the way it is supposed to be flown and apply precision to your touchdowns…” What do we mean when we say “…fly it the way it is supposed to be flown…?” The POH ground roll figures assume a minimum speed touchdown, meaning you’ve held the airplane off until, as it stalls you touch the ground. Hidden within that explaination are two nuances: first, it says you are going to hold it off for a stall, or near stall, landing, not plunk it on like a dead turkey at what ever speed you happen to have when you arrive in ground effect. Secondly, it automatically says you had the proper speed on final. If you’re too fast, the airplane is going to float like crazy and leave a lot of runway behind you. Plus, if you touchdown fast, the airplane will roll longer and take more braking.

We also said, “…and apply precision to your touchdowns…” What we mean by that is we don’t want to land just anywhere on the runway. We want it down in the first 500-800 feet, which is hardly a pinpoint landing, but is a range that will let you easily land on a 1500-foot runway. So, that means you have to have a plan in mind when you turn final that includes coming over the threshold at a reasonable height, say 15-20 feet, and on speed. If you do that, you’ll almost always touchdown at around 500-700 feet.

Ideally, we’d like to make that approach a power-off approach, but that’s not always possible, so we won’t get up on that soapbox. However, because we’re not talking about nailing it right on the numbers, you also don’t have to have it slowed way down, nose in the air while you grind down final riding the throttle. This should be nothing more than a normal approach in which you visualize the touchdown point just past the numbers and plan accordingly.

An absolute requirement is that you hold the POH recommended approach speed. If it says 85 mph, that’s not 82 and it’s not 88. It’s 85 and most modern airplanes are so speed-stable, when trimmed, there’s no reason not to have the speed dead on or close to it.

If the speed is right, it then becomes a matter of controlling the glide slope. The often-mentioned way to tell for sure where you’re going to touchdown is to use the runway numbers as your reference. If they appear to be moving away from you, or up the windshield, you’re going to be low. If they are moving down the windshield, or coming toward you, you’re going to be long. We want them stationary in the windshield as if we’re going to land on them, when, in reality, our natural float will carry us well past them.

Don’t aim short and depend on the throttle to get you the rest of the way because someday the power may not be there. Use configuration changes (flaps) to steepen the a glide slope that you know will get your there and don’t forget the good old fashion slip. It’ll scrub off the last ten or 15 feet with perfect accuracy. But, again, remember, we’re not trying to hit the numbers, just come over them at a reasonable height.

Once you get in the habit of always landing in the first 500-800 feet, you’ll be surprised how much longer every runway looks. Then, as you get better, shorten that distance to 300-500 feet and chances are, you’ll never find a runway where you actually need shortfield techniques.

In the real world there are very few really short runways, but there are lots of pilots who make them short by leaving too much runway behind them. BD

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