By Budd Davisson, EAA 22483
This piece originally ran in the June 2021 issue of EAA Sport Aviation magazine.
In 2019, depending on whom you believe, there were 5,050 public-use airports in the United States and close to 15,500 private-use fields. According to stats from 2013, 8,459 of the private-use fields had unpaved runways. However, of that number, one was more than 10,000 feet long while 6,760 were less than 3,000 feet. How much less “they” don’t say. Much more importantly, an unknown but huge number of unnamed runways are tucked into tiny valleys, nestled against farm wind breaks and running down the middle of isolated ridges 100 miles from nowhere. Statisticians don’t even know the latter group exists. However, backcountry flyers do. And the first time you shut the engine down after rolling to a stop on a backcountry grass strip and the impressive silence of the surrounding nothingness settles over you, the hook is set. Another flyer has found a new reason for being a pilot — backcountry aviating.
Backcountry Flying Lite Versus Bush Flying
Right up front, this discussion is not meant to talk you into converting riverbanks and sandbars into runways. Nor will the airplanes concerned be hyper-slow-speed, specialty airplanes wearing clown shoes that can roll over boulders and not even know they were there. The discussion is about using “normal” airplanes, maybe even C-172s (no, really!), to visit parts of the United States you’ve only dreamed about. At the same time, we’re going to discuss the dos and don’ts and, more important, the limitations imposed by the airplane, the situation, and the pilot.
One of the more entertaining parts of YouTube is that we have crazy airplanes doing crazy stuff being piped into our computers on an almost daily basis. Have you seen the “Dead Stick Takeoff” one? Very cool! However, these almost always paint an erroneous picture of backcountry flying. All of these videos are dramatic in the extreme, which is why they’re on YouTube in the first place. However, that is not the kind of flying most of us are likely to be doing, and they feature airplanes most of us probably aren’t flying. Still, that doesn’t mean that the backcountry is closed to the ordinary pilot flying an ordinary airplane. Some of it is, but there are a massive number of grass and gravel runways out there just waiting to be discovered. The neat part is that all of them are in seldom-visited parts of America. Better yet, we don’t need gigantic tires or specialized bush birds to make those flights. The same airplane that takes us to visit grandma can open the door to adventure that looks and feels adventurous, but is well within the reach of almost all pilots and many common airplanes.
Let’s get the tire thing out of the way first: Giant tires, the 29- and 31-inchers, have become something of a boulevard cruiser artifact. Their looks convey a bush image, but we see them on a lot of airplanes that will never touch dirt. They’re like the jacked-up 4-by-4 trucks around town that have tractor tires and riser kits but not a speck of dust on them. In our area (Phoenix), no matter where you are in town, there’s always at least one of those in sight. Most are all hat and no cattle. The fact that you can buy spray-on mud via Amazon says it all.
For the average pilot, as opposed to one of the highly experienced bush jockeys, if you’re landing somewhere where those gigantic tires are actually needed, you probably shouldn’t be landing there in the first place. If the landing spot actually looks like a real runway — meaning it is clearly seen snaking through the grass or dirt with minimal ruts and potholes — giant tires aren’t needed. More or less normal-sized tires will handle most of those surfaces.
Normal-sized tires in this case means that if it’s a decent grass runway, no matter where it is, the 6.00-6 tires on your 172 will handle it fine. Ditto for whatever’s on your Bonanza. If you’re worried about it, go up a size or two. Some 7.00s will cover you, and 8.00s will give your 182 a slightly “bushy” look, but 8.50s (for some reason there’s a big leap in size between 8.00s and 8.50s) definitely make a statement on a 172 or Skylane, whether they’re needed or not. Going up a little in size is good insurance.
Invariably, when talking about backcountry flying, the first image that pops up is a Super Cub skipping along the water while landing on a sandbar in Alaska. The states in the western United States, which have backcountry flying opportunities as good as anywhere in the world, don’t get the press they deserve. The rest of the country is left out altogether. That’s a shame because even places like Ohio and Illinois, not normally thought of as backcountry states, have their share of runways and places to visit where you least expect them. There are very few northern states that don’t have backcountry runways on farms, parks, or other uncommon spots, meaning they aren’t paved and may or may not be on a sectional. Also, almost every state has a backcountry flying association — some more active than others — that is ready to take you by the hand and show you what you need to know while introducing you to a really interesting, enjoyable world. Google can help you find these associations.
Combating the Strangeness
What we’re talking about in landing on off-airport runways is aviating that, if you’re an average, middle of the road pilot, is guaranteed to take you out of your comfort zone. If we’ve spent most of our flying career visiting local paved airports, we all know that feeling of strangeness that sets in when setting up the first approach to a new airport. When first landing on backcountry runways, you can move the decimal point on that strange feeling over a couple of places. This is because a surprisingly large percentage of general aviation pilots have never landed on grass or gravel, much less in an area where the topography and runway location say you’re out in the boondocks. Even the tamest, smoothest, longest, easiest, grass runway has a huge amount of strangeness attached to it if it’s surrounded by nothing but mountains and trees. Unless you live in the mountain states, the topography definitely spooks you. And don’t forget that the East has mountains, too, and it has its own fascinating inventory of inviting runways. Unusual runway locations are not unique to the West.
For all intents and purposes, regardless of how strange it feels on final, landing on grass or gravel is the same as landing on pavement. The big difference is that braking will be less effective because the coefficient of friction is lower. However, that’s only a big deal if dealing with much shorter than normal runways. For the purposes of this discussion, we’re not going to talk about runways that are so short and so awkward that they unduly challenge an average pilot flying an average airplane. However, this assumes the pilot can put the airplane within a few hundred feet of where it needs to be put. This is a matter of training and proficiency. Without those, many of the runways we’re talking about should probably be avoided.
More Than Length Makes a Runway Short
While the actual length of a runway can make a runway short, quite often that’s not what makes them short. Among other factors, “shortness” is often a mental thing that is driven by what a pilot is looking at when turning base to final. For instance, a lot of pilots think a 2,000-foot runway is short because they’re used to 3,000-foot runways. By comparison, it looks terrifyingly short. However, in most conditions, there are very few commonly available general aviation airplanes that can’t work out of 2,000 feet with zero problems. The operative part of that sentence is “in most conditions.” It’s really easy for other factors to make 2,000 feet incredibly short.
A 2,000-foot runway in New Jersey (500 feet MSL) is a totally different runway than the same-sized one outside of Flagstaff, Arizona (7,000 MSL). As far as that goes, 100 miles south of Flagstaff in Phoenix, which is much lower (1,500 MSL) but hotter at 108 degrees Fahrenheit, which is very common during the summer, the density altitude becomes just short of 6,000 feet. In those temps, everything about the airplane, regardless of the type, is compromised, and piloting technique and the load being carried become critical. A 2,000-foot runway is still flyable but only if the airplane, the load and the pilot technique is matched to the conditions. It’s also important to remember that most airplanes can land much shorter than they can take off. So, it’s easy to paint yourself into a corner. Or wait until early the next morning to leave. Also, the climb-over-50-foot-obstacle distance varies considerably from airplane to airplane and in the varying conditions. At full gross and zero wind, a 172 might not clear that obstacle in those conditions.
Besides the actual physical length, the factors that make a runway short include:
- Aircraft type: The bigger the engine, the more wing, the more flap, the less weight, the better the airplane. Heavier, faster airplanes and those with low power need more runway. It’s as simple as that. A 172 is often marginal, but a 182, when light, seldom is.
- Pilot skill: Most of the performance charts on airplanes assume flying at gross weight at 55-60 degrees Fahrenheit (12-13 degrees Celsius), zero wind, at sea level. The better pilot’s operating handbooks (POHs) give performance at different weights and temperatures. However, every one of them assumes the pilot can fly the airplane at the appropriate speeds with proper glide slope control. If that’s not the case, none of the charts can be replicated in practice.
- Runway approaches: Obstacles at either end of the runway eat into the usable length both in landing and takeoff. Quite often, this is a determining factor of whether taking off or landing is safe unless the airplane is lightly loaded, temperatures are moderate to low, and there’s some wind down the runway. These same factors apply to all airplanes on all marginal runways.
- Runway surface: Grass offers less braking on landing and causes more physical drag on takeoff. All of which requires the airplane to use more runway than usual. Dirt and gravel have the same effect but not as severe.
- Topography effects: Sharp drop-offs at the end of the runway, hills, cliffs, and ridges all can affect the pilot’s ability to put the airplane on the numbers, even if no obstacles are present on centerline. Also, even the slightest runway slope, either up or down, greatly impacts the ability to land and/or take off short.
- Wind conditions: Only a few knots of wind on the nose or on the tail will greatly change both landing and takeoff performance. For instance, a relatively small wind on the nose can often offset the effect of a down-sloping runway on landing.
The following numbers on the effect of varying takeoff conditions were assembled out of several mainstream POHs.
Factor Increase in Factor Increase in Takeoff Roll
Weight 10% 20% (plus more distance for 50-foot obstacle)
Altitude 10% 10%
Temperature 10 C, 18 F 10%
2% slope 40 feet on 2,000-foot runway 20%
Tailwind 10% of takeoff speed 20%
Grass Dry 20-25%
So, if you’re taking off on a slightly uphill grass runway, you have 20 percent increase in distance required for the slope and another 20 percent for the grass. Suddenly, the runway gets very short so the temperature better be low, the wind high, and the airplane light. These kinds of conditions clearly make some four-place airplanes into two-place, low-altitude, good-approaches airplanes. There’s a reason you see more 182s at backcountry fly-ins than 172s.
Weak piloting technique, combined with not properly recognizing the effect of the present conditions, often causes more accidents than the length or location of the runway. Both of these factors are easily curable with a little training and exposure to the real thing. While backcountry lite flying isn’t horribly demanding or difficult, it is different. Unless a pilot is experienced in the airplane under the new conditions, a couple hours with a CFI who is experienced in backcountry conditions is good insurance.
There’s a whole new world out there waiting for you, and you don’t need big tires or a bushplane to visit it. However, there should be a warning label attached to this kind of flying. The placard would read: “Caution. Potentially Habit Forming.”
Budd Davisson, EAA 22483, is an aeronautical engineer, has flown more than 300 different types, and has published four books and more than 4,000 articles. He is also a flight instructor primarily in Pitts/tailwheel aircraft. Visit him on AirBum.com.