Trees or power lines at the threshold may be so common that we're almost used to them, but they can generate their share of heartburn, which increases significantly when other parameters are factored in. Let's say, for instance, that there's a tree line right off the end of a 2,000-foot runway. That sounds short, but, depending on the airplane, it really isn't. There's 10 knots down the runway and you're flying a Cessna 172. No sweat, you say. Just keep it low to the trees and you'll have plenty of runway. A no-brainer, right?
OK, now, let's say the wind dies. The runway now seems a little shorter, doesn't it? Still, it's not a breath-taking challenge.
Same trees, same runway, but this time we make the runway slope a few degrees downhill. Whoa! No wind, slight down grade - now it's starting to get your attention, and you wish those trees would disappear so you could use the entire runway. Still, it's doable as long as you don't waste any runway.
Now we're really going to toss you a curve: The Cessna 172 is now a bigger, heavier Beech Bonanza that's loaded to the gills. So, now we're operating in a dead calm wind with tall trees on the threshold of a downward-sloping, 2,000-foot runway that won't let you come in from the other end because of an even bigger obstacle. Suddenly, this no longer looks like fun.
Oh, yeah, did we mention that the runway is at 4,500 feet mean sea level and the temperature is 98 degrees Fahrenheit with 87 percent humidity? Well, at least this'll give you an excuse for the sweat rolling down your forehead. Let's face it: There are some instances when it's time to go looking for another runway.
The point to all of this is that the term tough approach can have different definitions.
The definition changes not only because of what surrounds the runway and what lies on the end of it. But it also changes based on what kind of an airplane you're flying.
Make no mistake, some approaches are lousy regardless of the definition. A particularly memorable one in our logbook required snaking down a narrow, twisting canyon well below the rim. Then you had to get the flaps out and slow to approach speed before making a tight, 110-degree turn around a bend in the canyon as you chopped the throttle and prepared to flare onto a tiny pasture that lay next to a river. The takeoffs were fun too.
Most airport management teams have done their best to eliminate as many runway obstacles as possible. Even so, the most benign obstacles or seemingly unimportant aspects of the runway topography can present problems. In fact, even a runway that doesn't have an obstacle anywhere near the final approach can be a challenge given certain conditions. Let's look at how things that surround an airport but don't lie on the centerline can make life interesting.
For years we flew off of one of the most interesting and most beautiful airports in the country - Andover-Aeroflex in northern New Jersey. The airport is an excellent case in how topography can make an airport change personality in minutes, even though the approaches are clear. Aeroflex's tidy little 2,000-foot runway sits in a narrow valley with each end of the runway coming to a halt right at the edge of a lake. Both approaches couldn't be clearer if you paved everything for a mile off of each end. Still, under certain conditions, flying final can dry your mouth out so much it's impossible to whistle once you've landed.
The fact that the runway is 2,000 feet long has only a little to do with the challenge. About 300 feet from the centerline a 600-foot (I'm guessing) ridge runs the full length of the runway, plus there is an abrupt four-foot difference between the runway level and the surface of the lakes on each end. Most of the time, the airport is a little piece of heaven, but given the right (or wrong) conditions, it can be the nastiest little airport most folks will ever fly into. It all depends on the wind, and it is the airport's ability to periodically challenge you that makes its approaches so much fun.
Let's take the differential of the runway height to the lakes first: If the wind is blowing pretty hard you can look down on final and see what is awaiting you by studying the waves in the lakes. They will all be parallel and running in one direction except for a 100-foot square right at the end of the runway. There the water will be thrashing every way but straight because there is a significant curl bending down right at the threshold. If you decide you are going to plant it right on the end (2,000 feet looks short to some folks), there is at least a 50/50 chance that a downdraft will try to suck you into the water. When that happens, you'll probably hit the power too hard in an effort to break the downer. In less time than it takes to think about it, you'll find yourself 50 feet in the air, whistling down the runway wishing it was longer because you now have too much altitude and too much speed.
If the wind is from the east, there can be some turbulence on final. However, when the wind is from the west, you'd better buckle your seat belt and keep your tongue from between your teeth because you're in for a real ride! A westerly wind produces a sometimes-monstrous curl over the ridge that lies on top of the curl that's already right at the end of the runway. The net result is that something as light as a Cessna 172 is going to need just about all of its control authority to keep the airplane on glideslope. Making matters worse is the wind shear that may be hidden in all of the turbulence that produces airspeed excursions of as much as 10 kt. When most folks see the airspeed changes for the first time, they immediately tack 15 kt on their approach speed and drive down final like a freight train. Wrong!
Adding a lot of extra speed just because you're seeing some airspeed variation and are worried about the wind is almost always a mistake. Yes, it's common practice to add half the gust spread, but don't get crazy about it. At Aeroflex, you're damned if you do and damned if you don't. If you're slow, the downers will take your breath away. If you're fast, however, the fun really begins. The extra speed lets you punch through everything that's being thrown at you, but the second you're over the runway and in ground effect, you suddenly realize you're under the curl caused by the ridge and past the curl at the end of the runway. Most of the turbulence is gone, as is most of the crosswind component, and now you're so fast it'll be a miracle to get it down safely on the remaining runway.
Andover-Aeroflex is an example of an airport that has flawlessly clear approaches, yet flying final can be an ordeal that many folks can't handle. Other airports have similar hidden approach gotchas. One of our favorites is a beautiful 3,500-foot strip that ends right at the edge of a 100-foot cliff. It's scary-looking. The same curl problem exists on any runway with a huge drop-off, so how do you fight the curl? You don't. Unless it's a seriously short runway, just fly a slightly higher approach and plan to land a little past the numbers, and chances are you'll come in over the curl and never even know that it's there. "But what about runway length?" you may ask. Think about it: If there is enough curl to be a problem, that means there's a fair amount of wind down the runway so you'll need less distance. Also, most runways are 2,500 feet or longer and if you land most general aviation airplanes in the first 800 feet they'll practically coast to a halt on its own before reaching the opposite end - if you aren't carrying a lot of extra speed.
A common example of the "side runway obstacle" is buildings that have been erected on either side of the ends. Many airports are trying to survive in quickly developing urban centers, and developers can't be stopped from erecting buildings just outside the required clear zones. What results is an uneven windbreak of buildings of varying heights. When the wind gets crossways, the variations in wind and attendant curl makes the last part of the approach an iffy - sometimes turbulent - proposition.
Keep in mind that new development can change the wind patterns around the wind reporting stations enough that you can't really trust the wind reports.
Consider a body of water or different-colored ground that heats at a different rate than everything around it. A local airport has a canal running across the end of the runway, and during the summer it causes an unpredictable curtain of unstable air that must be compensated for. Most of the time, it's an updraft that screws up your otherwise perfect glideslope, while part of the time it sucks you down. In either case it's possible to get airspeed variations. Unless these variations are rapid and severe, you're better off holding the nose in the position that held your approach speed going into the updraft rather than chasing the speed. Every upper will end, and if you are chasing the speed when the upper decides to drop you, you're going to be wildly off speed for the rest of the approach.
And then there is the common trees/wires-on-the-end approach. People have a tendency to intellectualize this kind of an approach too much because it takes a really high obstacle sitting right on the end of a fairly short runway to actually make that approach unsafe in terms of runway length. There is seldom any reason to come in growling low over the trees, flaps down, and nose up at stall-plus-5-kt intending to drop it over the edge of the trees at the last minute. Remember what we said about rollout distance required for most light aircraft? Just plan to land in the first quarter and you'll be much safer than if you insist on doing a slow, edge-of-the-envelope approach right over the trees. There's a famous bush pilot saying that applies here: It's much better to roll off the other end at 5 mph than it is to stall it into the trees 20 feet short.
If flying a normal straight-in approach, one way to make sure you'll clear the trees or wires is to watch the top of the obstacle and the way it appears to move in relation to your touchdown point. The touchdown point will appear to be stationary in the windshield, and the tops of the trees or wires should always appear to be moving down the windshield or toward you. That clearly indicates that your glideslope is high in relation to the obstacle. If the top of the obstacle ever stops moving or moves up the windshield or away from you, hit the power and think about going around, because you aren't going to clear the trees from that position at that glideslope.
We mentioned a down-sloping runway earlier. While this is more of a runway condition than an approach parameter, it still figures into the equation. A runway with a gentle 2- percent slope (40 feet in 2,000 feet) requires approximately 10 percent to 20 percent more runway to get stopped, depending on the surface. If the runway length makes it tight, think about trying to land the other direction. If that can't be done, go home and wait until there is more wind down the runway.
Ninety-nine percent of the time our trip down final approach is a pleasant ride where we have plenty of time to orchestrate our arrival with few distractions other than the wind. It is, however, the other 1 percent for which we should be training. If there is one goal in landing on an airport with challenging approaches, it is to visualize the line through the air that will put us right where we want to be on the runway and that will conquer all of the challenges of the approach. Then we do what we have to do with the airplane to fly that line and we are determined not to let anything push us off of it. It's in those situations that we will take control of our destiny and not let any type of airport environment push us around. If we feel we can't do that, then it's time to do the smart thing and go looking for our alternate airport.
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