I had a next door neighbor named Ernie who was 95 years old. One Sunday he invited me over to watch the football game with him. As I sat there he kept yelling at the TV, as if giving instructions to the players. As politely as I could, I said, "Ernie, they can't hear you." He grumbled, looked over at me and said, "Oh, that's right, they got their helmets on."
In Part 1 of this series we discussed three important rules to follow during an emergency landing in unfavorable terrain. Rule number three suggests letting the airplane and the environment absorb the energy of impact. A good rule, indeed. But there's more to this rule than is apparent.
Figure 1A shows a Baron perched on the side of a mountain near Monterey, California. The pilot was on an IFR flight plan, in the clouds with three passengers onboard. He became distracted, lost navigational awareness, flew up a canyon and came to rest in a grove of trees on the side of a hill (Figure 1B). He didn't plan for this crash at all. In other words, his door wasn't open, seats weren't slid back, the master switch wasn't turned off, etc. Nevertheless, he and his passengers walked away from the airplane with only minor injuries.
Looking carefully at both pictures, you can see that the airplane's structure absorbed the impact very nicely. Nicely enough, that is, to allow the breakup of dispensable structures (wings, engines, tail surfaces, gear, etc.) over a long enough distance, thus preventing excessively high G forces as we discussed last week. Although we can't see the trees behind the airplane, it's reasonable to assume they won't need pruning this season.
If I had to speculate, I'd say the airplane probably experienced around 9 G's during landing. I base my estimates on what appears to be a cockpit starting to disassemble (see last week's article for more info on G-force). Perhaps the majority of cockpit damage is attributable to the rather large tree appearing to the copilot's side of the airplane (Figure 1C). It looks like the airplane came to rest against this tree when its speed had already slowed considerably.
I suspect that an additional factor in the survivability of this crash was the angle at which it occurred. The airplane managed to hit the tree tops at a relatively shallow angle with a low sink rate, which is a perfect configuration when landing on this type of foliage. Of course it's desirable to touch down at the slowest possible speed, with a "zero" sink rate prior to contact. As we mentioned in Part 1 of this series, stalling into the trees isn't a good idea since it can lead to loss of control of the airplane.
The question is: If you had to put an airplane down in unfavorable terrain, how would you choose what to hit and what to avoid? There are two answers to this question. First, under all circumstances, avoid directly hitting anything with the cockpit. Second, if you have to hit something, let the frangible (breakable) parts of the airplane (wings, gear, horizontal stabilizer) do the hitting.
It's obvious that hitting saplings is much better than hitting something on the order of ancient redwoods. This is similar to seeing a big guy whooping a little guy. If you're going to jump in and help, it's much safer to help the big guy whoop the little guy. After all, you have size going for you (I'm just kidding about helping the bigger guy). But I'm not kidding when it comes to trees. In an airplane, go for the little guy, the little trees.
If the foliage is thick, shallow the glide angle and slow the airplane down as you approach the tree canopy. A high angle of attack just prior to contact gives you the additional benefit of protection from the bottom of the fuselage. It also keeps tree branches from directly hitting the windscreen.
If the saplings are spaced farther apart (wider than the width of the fuselage) and don't have much of a crown to them, then there's little benefit from attempting to land on the tree tops. In this case, aim your airplane between the saplings and plan your trajectory to hit closer to the ground.
A military briefing I read once suggested that the bigger the airplane, the lower the pilot could hit the tree trunk. The assumption here is that a more massive airplane can afford to hit the thicker portion of a tree trunk since it has more momentum to dissipate. A less massive airplane (like the ones we fly) is better off hitting trees higher up where the trunk or branches are smaller.
Don't, however, contact the trees too high up. The average person can't survive a fall from an altitude of 50 feet or more. Falling from 50 feet is like falling from a four story window. Hitting trees at the 50 foot level or higher may result in serious or fatal injuries.
Additionally, try making your contact with trees (any size tree) symmetrical. In other words, both wings should absorb energy equally. This becomes even more important when the tree trunks are bigger.
Figure 2A shows an emergency landing made by James Stone and his wife D'Ann in their Cherokee 140. An exhaust valve stem failure resulted in a power loss when they were over the Everglades National Park. James descended for a final approach over a mangrove hammock at the west end of a grassy field. As he got closer he recognized multiple picnic tables and grills that were scattered in his planned landing area (sometimes you can only see these things close up).
He chose to miss the steel based tables and barbecue grills (good choice) and aimed his aircraft between two palm trees. Both main tires were on the ground when he hit one palm tree with the left wing. Figure 2B shows Jim pointing to where the tree was originally located. Figure 2C shows the approximate size of the tree Jim hit (notice the circular indentation on the wing). The wing severed from the airplane (Figure 2D) and the airplane rolled over on its back. As the airplane slid to a stop inverted, it came to rest in such a way that it jammed the passenger door (there's only one passenger door on a Cherokee 140).
Jim had to kick out the pilot's window to provide an exit for himself and his wife. They walked away with only small bruises. As I understand it, a fellow camper arrived on the scene, saw James and his wife and asked, "Hey, how did you folks get here so fast?" I believe Jim said, "Ahh, we flew in." You've gotta keep your sense of humor in these conditions.
Several lessons are apparent from Jim's accident. First, things look different from the air than they do from the ground. The next time you happen to drive by a grove of trees, imagine what these trees look like from the air. Examine the tree canopy, tree density and trunk width, and then imagine the outcome of impacting them during an emergency landing. Develop an idea about what is or is not acceptable foliage upon which to make an emergency landing.
Second, contacting an object with only one wing may cause the airplane to roll inverted. This could prevent easy egress. Nevertheless, it's good to know that the average person, if motivated, can kick out a single-pane window if the exit door is blocked.
Third, there's a hidden lesson in the way the airplane's kinetic (movement) energy dissipates when one wing strikes a tree.
Striking a tree with one wing typically causes the airplane to roll about its vertical axis (yaw) or about its longitudinal axis (roll) or both axes. No doubt that Jim chose wisely in hitting a tree with one wing rather than striking it head on with the cockpit. Why? Rolling helps dissipate the airplane's kinetic energy. This is a very important concept to understand.
If you ever get a chance to watch movie stunt drivers, notice how they carefully plan the impact of their automobiles. They always strive for the glancing blow while avoiding head on collisions. Hitting an object with the side of a vehicle (the wing, in the case of an airplane) prevents sudden stoppage and sets up a rolling or spinning type motion. This allows more parts of the vehicle to absorb the impact energy. In the case of a car, all four fenders, doors and engine help absorb this energy. An airplane uses its wings, horizontal stabilizer, gear and engine to so the same.
In September of 1983 my friend Danny Mortensen crashed a Rutan racer after an encounter with wake turbulence while racing at Reno. The turbulence rolled Dan's airplane inverted causing it to strike the ground cartwheel-like at over 200 mph and roll several hundred feet. Dan walked away from this crash with only scratches to his fingers. There wasn't one person in the crowd who thought he was still alive.
What saved Dan was the rolling (cartwheel) motion of his airplane. Rolling allowed the airplane's wings, engine and gear to absorb the impact energy. He had the additional benefit of being in one of Burt Rutan's composite airplanes--a very strong aircraft. Additionally, he wore a helmet and had a multiple-strap seat restraining device.
My friend Dean Engelhardt was a professional movie stunt pilot. He's crashed over 14 airplanes on purpose. His secret is to avoid head on strikes with the airplane he's flying. In preparation for a spectacular crash in a Cessna 206, he put the airplane in a forward slip and hit the ground left wing first. This sets up a rolling, cartwheel-like motion which helped dissipate the energy of impact. The wings, horizontal stabilizer and engine were destroyed in the process while leaving the cockpit relatively in tact. Dean says that most crashes culminating with a cartwheel-like motion versus a head-on type impact typically result in less than serious or fatal injuries.
What's the point here? Am I telling you this because I want you to do exactly what Dean did in crashing the 206? Not really. Neither you nor I am qualified to do such a thing, even if the airplane is a rental. We're better off letting the environment (trees, fixed structures, etc.) absorb the energy of impact. If it looks like a direct collision with an obstacle is likely, then use the glancing blow concept. Avoid a head-on strike. Try to hit the obstacle with the side (the wing) of your airplane like Jim did. This is they key to minimizing injury when making an emergency landing in inhospitable terrain.
In Part 3 of our series, we'll continue our investigation into preparing for the crash landing. Remember, the information contained in these articles is meant to help prepare you for those very, very rare events when you're forced to land in inhospitable terrain.
For more information on this subject, see "Learning Experiences: Emergency Landings" and "The Long Wait: What To Do Until Help Arrives."
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