Short-Field Ops

What Makes a Runway Short?
The Psychological Factors
Ignoring everything having to do with an airplane's performance, a runway is universally considered short when it's significantly shorter than what we're used to. It's a mental thing that may have nothing to do with reality because almost every "normal" general aviation airplane (as opposed to special short-field birds) will land and take off in a space that's far shorter than the average pilot is willing to challenge. For instance, a quick study of available stats shows that a Cessna 152 requires less than 500 feet to stop, while Cherokees, 172s and such all fall into a required runway range of 550 to 650 feet. Bonanzas fall into the under-800-foot range. These are factory specs, measured at gross weight with zero wind, around 60 degrees at sea level with moderate (not severe) braking.

Look back at those numbers, and yes, they're accurate. But, they're rollout distances only, measured at the factory from where the tires first touched to where our trusty bird stopped. But, even if we were to add 300 feet to each, how many average pilots are willing to take their C-172 and such into a runway that's less than 1,000 feet long? In fact, how many pilots, in general, have ever turned final to 1,000 feet of runway? It looks tiny. Impossible to land on! It's very intimidating, and many pilots would avoid it, if given a choice. Other pilots who love short-field work, however, wouldn't bat an eye at it because it's not out of their comfort zone. So, short is relative to what we're used to. However, there are other factors that do make a runway short.

Real-World "Shortening" Factors: Stuff We Have To Deal With
First, it could be said that what's short for one airplane can be too much for another. A thousand-foot runway in a Cub is like turning it loose at JFK, while a loaded Cirrus might be out of luck: It needs 1,140 feet to land and 1,600 to take off. Most aircraft require more to take off than land. However, ignoring the limitations of the hardware, other non-aircraft related factors can make a runway short almost regardless of its length.

Bad approaches. Tall trees, etc., at the thresholds can make a 3,000-foot runway short because not all of it's accessible.

High altitude. Thin air means the airplane will be carrying more ground speed than at a lower altitude, and the engine won't be putting out as much horsepower.

High temperatures. Along with altitude, temperatures increase/decrease the density altitude and can greatly affect the way an airplane can perform on a given runway.

Runway slopes. Sometimes slopes, even minor ones, make a runway longer: landing uphill or taking off downhill makes a huge difference. Just the reverse is true if approaches make it a one-way runway that forces us into landing downhill and taking off against the slope.

Runway surface. Several factors about runway surfaces come into play when trying to get stopped after landing or building up speed for takeoff. Grass is nature's lubricated surface that offers less traction for landing and tries to slow acceleration for takeoff. Rough surfaces have the same effect, and grassy or soft, sandy surfaces even more so. Wet, soft surfaces claw at the tires, trying to hold them back on takeoff, but offer no braking resistance on rollout. Not a good thing.

Wind is our friend, unless! Wind is the short-field pilot's friend unless it's trying to come from behind the wing or is creating significant turbulence. Gusts are the enemy: When you're hanging it out at minimum airspeed, the last thing you need is a gust dying.

Here are some factors compiled from various factory POHs.

Pilot Techniques (Or The Lack Thereof) That Shorten Runways
Given that something like a fully loaded C-172 theoretically needs only 600 feet (give or take) to land and around 850 feet to take off (no obstacles), you have to wonder why people think a 2,000-foot runway is short. Normally, they wouldn't, but there's that obstacle thing to deal with. A loaded 172 may take off in 850 feet (sea level, 60 degs F) but it needs 1,550 feet to clear a 50-foot obstacle. If working at 5,000 feet MSL at the same temps, add nearly 50% to those numbers. Incidentally, the mythical 50-foot obstacle is the rough equivalent of a five-story building. That's a pretty tall tree! However, notice that until we get up to higher altitudes, 2,000 feet of runway even handles the 50-foot obstacles. So, we ask again, what's happening that makes pilots think a 2,000-foot runway is short, when apparently, it really isn't? The obvious answer is that piloting techniques aren't letting us optimize the aircraft's performance, so we can't utilize all the runway has to offer us.

Leaving too much runway behind on touchdown. This is the single biggest factor why reasonable-length runways are viewed as being short. This is why minimizing runway left behind while touching down is always the goal in short-field landings. At the same time, maximizing aircraft performance on takeoff is the goal on takeoff. Both of these often suffer from inadequate piloting technique, as below.

Lack of speed control. The POH often gives an optimum short-field approach speed. Sometimes, it doesn't. In either case, arriving over the threshold with excess speed means excess float. So, we're not able to nail the point we want to touch down on. The POH also gives an optimum best climb angle speed and any speed over or under that means we're compromising climb. More on that later.

Inaccurate glideslope control. The name of the game is to put the airplane as close to the end of the runway as obstacles will let us without compromising safety. Remember: It's much better to roll off the other end of the runway at 10 mph than to land 10 feet short. But, with good glideslope and speed control, neither should be a concern.

Uncoordinated flight. Except when slipping, every time the ball wanders off center, unwanted altitude is lost, and performance/safety are compromised. When flying close to the lower airspeed limits, keeping the ball centered is critical for both performance and safety.

So, How Do We Do it?
Right from the get-go, we should establish that there are several different concepts people use to land an airplane short, however, they all endeavor to do the same thing: put the airplane on a given spot close to the threshold at minimum safe speed. It's a given that the stall speed is obviously too slow, but how much of a margin we keep over that, and how that margin is established and maintained, is central to the differences between the two approaches folks use.

Visually establish a touchdown point OR an obstacle clearance point. When practicing short-field approaches, it's seldom we have obstacles to worry about. Invariably, we have a clear shot at the threshold, so can pick the spot on which we want to land. This should NOT be the actual threshold of the runway because a miscalculation would result in touching down short, which can be catastrophic. When practicing, pick a point at least 100 feet down the runway. We then try to visually keep that point stationary in the windshield with power while coming down the glideslope. Basically, the throttle follows the point. If it appears to be moving up the windshield, we're low and the power goes in. If it's going down the windshield, we're high, so the power comes back slightly. Power adjustments should be tiny and smooth, but be prepared to ram it all in a go around, if things aren't perfect.

If working with obstacles, the visual point that we're tracking in the windshield can be the top of the obstacle: We always want it moving down the windshield (or moving toward us), verifying that we're going to go over it. Ideally, we'll be high enough with a steep enough glideslope that we can see our touchdown point at the same time, although one school of thought has us dragging the airplane over the obstacle with power, throttling back momentarily and dropping down to the touchdown point.

Concept one: glideslope control via power dependency. In both concepts, the goal is to take advantage of the way an airplane reaches a speed on approach, where it suddenly wants to come down quickly even though it's still well above stall speed. When it reaches that point, it's dependent on power to help keep the glideslope pointed at the touchdown point and prevent us from arching toward the ground well short of the runway. How that speed point is reached is the difference between the two concepts.

One school of thought has the airplane turn final at normal approach speed and full flaps. A target speed is established in our minds (say stall plus 8 mph) and, as we close on the runway, the airspeed is gradually reduced, and the power becomes increasingly important in holding glideslope. In this approach, the glideslope angle can be steeper than normal, and speeds don't get down into the danger zone until fairly close to the runway. At this point, the airplane is literally guided by the throttle.

As the touchdown point is approached, power is slowly bled back, letting the airplane down. However, care has to be taken that the nose isn't started up for flair until the last second, and the power is still on at that point. If the power is brought back before the aircraft is flaired, the speed will bleed off very quickly, and the airplane will hit hard. It's better to keep the power on as the nose comes up, and gradually bleed the power and let the airplane down onto the point. Don't just chop the throttle or the aircraft will plop onto the ground. A bounce eats up runway distance and destroys braking.

Concept two: totally power stabilized approach. Both concepts arrive at the touchdown point the same way: slow with power controlling the descent. However, some will establish the target speed (stall plus a little) much further out, making the airplane power-dependent much earlier and using the throttle to draw a pool- cue straight line to the touchdown point. Some claim this also facilitates dropping down over an obstacle to get at the threshold closer to the tree line.

Takeoffs are mechanical. On takeoff, the goal is to get off the ground and to best angle speed (Vx) as soon as practical. Normally, we'd drop the hammer, get up to speed and rotate hard, flatten out immediately to accelerate, and nail it on the proper climb number. However, in real-life short-field situations, the runway surface often complicates things. Namely, grass, etc., can slow acceleration, so the takeoff is a combination soft and shortfield. Nose gear is hoisted out of the grass, mud, etc., as soon as the tail has enough power to do so, but angle of attack is minimized so not too much drag is generated. It's a tradeoff because that slows getting the mains out of the muck, so a happy balance between the two is struck. The combination is determined entirely by the situation at hand. If there are no obstacles, then getting to Vx is irrelevant and getting off the ground has priority, and that, again, determines the technique.

Practice Makes Perfect (Or At Least Safe)
Shooting short-field landings and making short-field takeoffs is terrific for building precision in our flying in a way that can actually be measured. However, it should be mentioned that this is the type of practice that starts with a CFI on board, if nothing else, to monitor how we're doing with our speed control because we don't have much margin to play with. Regardless, this area is one of the more fun things we can practice. Better than that, suddenly every runway we encounter seems a whole lot longer.