viernes, 8 de julio de 2022

How To Pick An Off-Field Landing Site If Your Engine Fails


During a power off landing, you're faced with some serious decisions.

So what happens if you've determined your engine isn't coming back to life, and you're not within glide range of an airport? You need to pick the next-best landing site. Fortunately, you usually have quite a few options.

Preparing For An Off-Field Landing

When you're preparing for a power-off landing, there are two primary things you need to consider to make your landing survivable (for this article, we'll assume the aircraft is not equipped with a BRS).

First, you need to keep the cockpit and cabin as intact as possible by using dispensable parts of the plane, like the wings, landing gear and bottom of the fuselage to slow you down during landing.

And second, you need to prevent your body from hitting the inside of the cockpit during touchdown, by making sure your seat belt is tight. Like the saying goes, airplanes are replaceable, but people aren't.

Rapid Deceleration

Most GA airplanes are designed to protect you at up to 9Gs of forward acceleration. Look at the example below. If you're flying at 50 MPH, the required stopping distance at a 9G deceleration is about 9.4 feet. And if you're flying at 100 MPH, the required stopping distance at a 9G deceleration is about 37.6 feet.

Think about that for a second: 37 feet isn't a lot of required stopping distance in a survivable crash. In fact, it's just a little bit longer than the fuselage length of your plane.

Finding A Spot To Land

When you're looking for a place to land, there are two common spots you're going to look: fields and roads. Unfortunately, both of them come with their fair share of risks. But if you pick a good spot, chances are very high that you'll walk away from the landing.

First let's look at fields and different types of terrain. Most of the time you're looking for an open field with a relatively flat place to land. But fields don't have to be completely open. Landing in dense vegetation, like a corn field or an area with brush or small tress actually does a very good job at stopping an airplane. And believe it or not, many times an airplane that lands in areas like these is repairable and can fly again.

Picking an open field is obviously one of the best options for landing. It gives you plenty of room to maneuver, set up for landing, and land into the wind. Plus, most fields are big enough to get you plenty of wiggle room, if you end up short or long of your landing spot.

But you might not be lucky enough when your engine fails to be over the perfect field.

Bad Landing Spot? You Can Still Put The Odds In Your Favor

If you're landing in a forested area, chances are you're going to be landing in the trees. And while landing in tree grove wouldn't be your first choice, there are a few things you can do to make it survivable. You'll want to use a normal landing configuration with full flaps, and land into the wind, so your ground speed is low.

When you "touch down" on the tree tops, you want to be at the slowest airspeed possible without stalling, so you can hang the airplane in the trees in a nose-high attitude. By keeping the nose high, the entire bottom of the plane can cushion your initial impact, as well as keeping branches from breaking through the windshield.

When it comes to choosing the right trees to land on, you want to try to pick trees that are low and closely spaced, as opposed to tall trees with thin tops. It might be hard to convince yourself the dense trees are the better option, but they can cushion your descent all the way to the ground. On the other hand, a free fall from the top of a 75 foot tree ends with a 4,000 foot-per-minute impact when you hit the ground, and that's going to hurt.

If you're in a confined area, like the mountains, there aren't always a lot of good options, and crashing into the side of a mountain definitely isn't one of them. In a situation like this, looking for rivers or creeks are some of your best options. Even though the area is confined, rivers tend to be fairly flat, and a touchdown in the water usually gives you a uniform deceleration, which is a lot more survivable than trying to land on the side of a 45 degree mountain face.

But there's something you need to keep in mind no matter where we choose to land. You need to use the plane to save yourself, even if it means damaging the airplane in the process to help you slow down and come to a stop.
Controlling Attitude and Sink Rate

When you're landing off-airport, the most critical mistake you can make is not controlling your aircraft attitude and sink rate. Fortunately, you can control both of them all the way to touchdown, even when you're power-off.

No matter where you are, if you land in a nose-low or level attitude, you risk sticking the nose into the ground. That's going to flip your plane, or make you stop very quickly, which can easily cause more than just a few bumps and bruises.

Steep bank angles before landing are just as bad. When you're at a steep bank, your stall speed is significantly higher (at 60 degrees of bank, your stall speed is 40% higher). On top of that, if you strike one of your wings on the ground, or anything else that's sticking out of the ground for that matter, your plane will cartwheel, making the landing less survivable than a straight-ahead deceleration.

No matter where you're landing, you want to set yourself up for a straight ahead, nose-high landing into the wind, so you can land at a slow groundspeed, and use the airplane to protect yourself.

How Should Your Aircraft Be Configured For A Field Landing?

So what should you do with your flaps when you're landing off-field? Flaps let you fly at slower speeds before stalling, which is obviously a good thing. But they also significantly decrease glide distance.

You need to be careful about adding flaps too early in your setup for an off-field landing. Otherwise, your best laid plans will go out the window, and you'll end up landing somewhere you really don't want to be, as opposed to somewhere that's a decent landing spot.

Landing gear position is another thing you need to be thinking about. If you're flying a retractable gear plane, you need to decide if you want your gear up or down during landing.

If you're touching down on something soft, like a plowed field, landing with your gear down means there's a reasonable chance your gear will dig into the dirt and flip your plane. So if you're faced with a soft field in a retractable gear plane, intentionally landing with your gear up might mean you'll have a slower deceleration. But if you're landing on a hard surface, putting your gear down helps cushion your touchdown, as well as decelerate your plane all the way to a complete stop.

Power-Off Landing On A Road

If you're landing on a road instead of a field, you have a new set of challenges. With roads, you need to deal with cars, power lines, and signs along the road. And while landing on a road is a little more straightforward than landing in a field, there are a few things you need to consider.

First, how much traffic is on the road? If there's a lot, chances are that you could hit a car as you touch down. And if the car is going the opposite direction, your impact is going to be intense. On top of that, your propeller, even though it's only windmilling, could cause serious damage to a car and passengers. So if the road has lots of cars, it's probably not your best option.

Next up is power lines, which can be harder to pick out. Power lines running along a road are typically far enough away that your wings won't hit them during touchdown. But powerlines that cross a road are a different story.

Finally, you need to consider the fact that highway signs are not your friend. Since the signs can hit your wingtips and probably send you into the ditch, you want to avoid them if at all possible.

Since the majority of highway signs are near road intersections, avoid landing in those spots to reduce your chances of clipping a "stop" or "speed limit" sign. Not that the speed limit sign is that important anyway - chances are you'll be going faster during touchdown.

Once you've picked a safe spot for a road landing, you want to set up just like a traffic pattern. You'll enter on a downwind leg, and turn base when you're abeam your touchdown point. Just like an airport power-off landing, you'll add partial flaps on base, and when you've turned to final, you'll add full flaps only when you're 100% sure you're going to make your landing spot.

After that, landing on a road is a lot like landing on a runway, except for the fact that roads are usually a lot narrower than a runway. If there's ever a time you want to land on centerline, this is it.

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