The Pilot’s Lounge #149: Crashworthiness Common Sense

It was a foggy mid-week morning when I stopped into the pilot’s lounge at the virtual airport. I was doing some research for an article in our sister publication Aviation Consumer and I needed Wi-Fi access, so I figured I’d tap into the flight school’s system. Karver, recently instrument rated and Kary, a long-time pilot and Civil Air Patrol check pilot, were headed out to get some practice in the clag before the fog was forecast to burn off.

We greeted each other in passing, but then Karver stopped and said to me, “Hey. If the engine quits while we’re out in low IFR, Kary told me that we won’t have much time after we break out of the clouds to select where we’re gonna land and that I should just aim for something soft and cheap. Is she kidding me?”

I did my best impression of a deer in the headlights and responded, “Um, well, not really. But, no matter how much time you have to choose a forced landing spot, there are some rules of thumb to keep in mind to maximize your chances of a surviving. Believe it or not, the little bug-smashers we fly are pretty crashworthy if you touch down right side up, just above stall speed and are wearing a shoulder harness. They’re even better if you have a BRS parachute on the airplane and have gone over the guidelines on its use. I’ve got some stuff on crashworthiness I can pull up and give to you after you fly.”

“Great. I’ll see you then.”

Pulling together the material for Karver turned into an interesting exercise in general aviation risk analysis. I made a bunch of notes.

There are things that pilots/aircraft owners can do to increase the chance of survival when everything goes bad and they’ve got to put the airplane down or they lose control during landing—the two highest risk events pilots face that can lead to a survivable ground impact (loss of control in flight, CFIT and VFR into IMC crashes usually result in high-speed, nonsurvivable impacts). I’ll start with a little background.

Since World War II there has been a massive amount of research into what the human body can withstand when in a vehicle during an impact event. In the aviation world, NACA/NASA did extensive full-scale testing of airplanes and occupant restraint systems and were joined by Cessna and Piper when those companies provided airplanes for crash testing. Sophisticated research is continuing, and the results have been progressively incorporated into general aviation aircraft design and design regulations. In general, even many of the 1940-era designs will do a fairly good job of protecting the occupants in a crash sequence if the three cardinal tenants of crash survival are followed: A. The occupants are fully strapped in—shoulder harness and seat belt, B. the speed of the initial impact is minimized (force is a squared function) and C. the airplane has as much space as possible to slow down between the initial impact point and where everything comes to a stop.

Restraining the occupants is step one. The nonsense still sometimes heard about people being “thrown clear” of an airplane in a crash is truly pure nonsense. A human ejected from a vehicle doing 50 MPH doesn’t survive the subsequent impact with the ground, trees or a building. The quick stop destroys internal organs and the aorta.

Keeping the occupant attached to the seat and in the vehicle means that the structure of the airplane can absorb impact loads that otherwise would be transmitted to the fragile human, reducing the G loading on the person. That means each person in the airplane needs to be wearing a seatbelt and shoulder harness—that way the person gets the benefit of the crashworthy design of the structure and is less likely to “flail” and strike some portion of the cockpit during the impact sequence.

Seatbelts alone are not enough. No human is strong enough to brace against a sudden impact of even two or three Gs toward the instrument panel. The body jackknifes over the seatbelt and hits something hard. A head injury means the risk of fatal injury goes way up. It also means that there’s a high risk that the occupant is dazed from even a low-G crash and can’t get it together enough to get out of the airplane quickly, generating a high risk of further injury if there is a fire.

The FAA has been keeping accident data for a long time: It reports that 88% of injuries and 20% of fatalities have been eliminated through the use of shoulder harnesses in general aviation crashes. Shoulder harnesses are as close to a silver bullet for crash survival as there is in aviation.

If the airplane has shoulder harnesses, common sense means wearing them all of the time. The greatest risk of a crash with loads that are survivable if you are strapped in is a forced landing after a power loss or a runway loss of control event. In either of those, things happen so fast that you won’t have time to put on the shoulder harness if you aren’t wearing it. Common sense is to wear the restraint system from before startup to after shutdown.

If your airplane doesn’t have shoulder harnesses, look hard at having them installed. They can be easily installed for most seats on all Cessna singles (they were generally available as optional equipment, even back in the 1940s, so a retrofit is often pretty easy). Aviation Consumer has a library of articles on retrofit shoulder harnesses free to subscribers as well as information on the new airbag seatbelt restraint systems available for retrofit.

Force of impact is a squared function. Doubling the impact speed mean quadrupling the force on the airplane that has to be dissipated. The airplane may have all of the most recent features for absorbing energy as the structure crumbles to protect the occupants, but if the machine is moving at cruise speed at impact, even the most sophisticated crashworthy design becomes irrelevant.

If you have any control over the impact speed, make it count. If you’re dealing with a forced landing following a power loss, strive to touch down as slowly as possible without stalling the airplane. Not stalling is important—if you stall, you lose control of the aircraft and you are likely to set up a high rate of descent and the nose may pitch down sharply, both of which are ugly for surviving the impact. You want to be descending at a gentle rate so that the airplane will roll or slide over the ground and not dig in so that it stops suddenly.

Using full flaps reduces the stall speed as much as possible, so that your touchdown speed is as slow as possible. This is not the place for a reduced-flap landing.

Do your best to touch down with no side load/yaw. The maximum crush space is directly in front of you. If you hit with a side load there is a risk that you’ll smack your head against the side of the cabin or one of the cabin support pillars.

When you maximize the distance that the airplane has to decelerate, you minimize the G loads on the occupants. The G-Load chart shows the ability of a healthy human to withstand impact G loads straight ahead—toward the instrument panel—if restrained with a seatbelt and shoulder harness. The variables are intensity of the load and duration. If you can spread out the impact so that the maximum load doesn’t exceed 10 Gs the chances of surviving the crash go way up.

That means that you not only touch down at minimum flying speed, but you keep steering the airplane toward where you want it to go—where the hard things aren’t—until it comes to a stop.

That rule applies to the accident that a general aviation pilot is most likely to have—loss of control after touching down on landing. If the crosswind takes you off of the runway, or you groundloop or blow a tire and you’re heading for the weeds, never give up trying to make the airplane go where you want it to go. Don’t be hesitant to put a control to the stop. Keep fighting to make the airplane go where you want it to go to minimize impact forces.

If you groundloop an airplane—the tail comes swinging around uncontrollably—keep the yoke/stick all the way aft. It will reduce the risk that the airplane will flip over and help keep weight on the landing gear, which may help you regain control of the airplane and/or use the brakes to get it stopped before you hit something.

If you get into the situation of having to steer the airplane through a maze of rocks and trees, keep in mind a rule of thumb that works: Look/focus on where you want to go. That’s where the airplane is most likely to go. If you are trying to avoid hitting a tree, don’t look at the tree—you’ll hit it. Look at the path you want to follow. It works with airplanes, cars and taking horses over jumps—you and the vehicle are most like to go where you are looking.

Use the brakes—to the point just short of sliding the tires. If you don’t know where that point is, practice on your next landings. If you’re in a tailwheel airplane, use the brakes firmly, but don’t let the tail come off the ground (you do have the stick full aft, right?). There can be a fine line between maximum braking and nosing over on a tailwheel machine. My review of accident reports over the years indicates that the Aviat Husky with its good brakes and gear geometry is an easy airplane to put on its nose—or back—with heavy braking.

If you have run off of the runway and are trying to get the airplane stopped, make sure that the throttle is at idle—I don’t know how many accidents I’ve looked at where the pilot added power to get airflow over the rudder while trying to control a swerve, lost control and then magnified the intensity of the crash by carrying power throughout the impact sequence. Do everything you can to slow down.

Oh yeah, wait until the airplane actually stops before undoing the restraint system and getting out.

There has been a great deal written about selecting where you should land in the event of a forced landing. The only thing that I will add is that the numbers for survival in water landings—whether the airplane has fixed or retractable gear—are amazingly good. In over 92%, the occupants are able to get out of the airplane safely. Overall, the survival rate for general aviation ditching events is 88%. That being the case, if you are faced with landing in trees, in a rocky field, on a beach or in the water, don’t rule out landing in the water about 50 feet or so offshore. It may be the best alternative for spreading out the deceleration forces and allowing your passengers to get out uninjured.

Should you land on a highway/freeway? That’s a judgement call based on a lot of factors, one of which is that your wingspan is longer than a two-lane road is wide, so your wings will probably hit signs, mailboxes, guard rails or whatever is erected along the roadside—and that may pull you into a unyielding ditch at high speed. In addition, powerlines are nearly impossible to see, and they are erected along and across roads. Catching one with the gear or a wingtip is a seriously bad-news event. If you have no choice but to hit lines, take them on the center of the prop.

If there is traffic on the highway you face an ethical question. As a pilot, can you put innocent people on the ground at risk just so you can increase your chances in a forced landing? That’s pretty easy if you’re solo—no. If you have a plane load of passengers? That’s worth doing some thinking about now.

The debate on this will never end. The commonsense rule is that if you believe that the surface is such that it will catch the landing gear and flip you over right away, leave the gear up. Otherwise, it is probably wise to take advantage of anything that can absorb impact energy before it is transmitted to you—the landing gear. Gear up, you have a fairly rigid structure with only a few inches of crush distance under the seats. The landing gear was designed to absorb energy. In some airplanes, such as the Cessna 208, the gear is designed to absorb loads that occur directly aft and then snap off, reducing the deceleration loads on the occupants.

Make sure the seat belt and shoulder harness are tight—if you have the time. Lean or curl forward into the shoulder harness to take out any slack. If you have time to put any padding in front of you—throw pillow, coat, blanket, anything—do so.

Turn off the master switch and the fuel prior to touchdown. An electrical short can start a fire. Shutting off the fuel helps minimize the chance that any fire will become severe.

Keep the airplane right side up. That sounds silly, but it is a killer in twins when the pilot can’t make the airplane hold altitude on one engine and gets below V_MC before touchdown. The airplane will protect the occupants against some serious G loads when right side up, but not upside down. If you have to make a forced landing in a twin, do what is necessary to avoid a V_MC roll.

Whole airframe parachutes have been saving lives for a generation. If the airplane has one, you’ve experienced an engine stoppage that you can’t fix or one of the other emergencies for which the parachute is designed, using it is a no brainer. Pilots and passengers have lived to fly another day because the parachute put the airplane onto the terrain (or water) at an impact speed that was survivable—and that’s the underlying goal of surviving any emergency.

BRS offers retrofits for a number of aircraft. Shoulder harnesses are the silver bullet for crash survival; whole-airplane parachutes may be the platinum one.

To start with, breathe. Make sure you have the airplane under control and are flying in conditions where you can divert your attention to getting the gear down without running into something or someone or losing control of the airplane.

Pull out the checklist. I’m not kidding. When I look at gear-up landing accidents, in about 10%, the pilot could have extended the gear if he had simply followed the published emergency checklist. (By the way, if you’re flying a retractable-gear airplane, you have practiced emergency gear extension . . .)

If the gear won’t come down, remember that you have an emergency situation but one that is very low risk so long as you don’t do something stupid. In the last 40 years I have tried to find an NTSB report of a gear-up landing of a civilian airplane in the U.S. in which someone was injured or killed. I have not found a single gear-up landing event in which anyone was hurt when the pilot made a normal approach and landing (many pulled the mixture around the time of the flare). Hey, a gear-up landing is such a minor event that it does not even classify a reportable accident—take a look at the NTSB regs on accident definition.

However—and this is a really big however—there have been several fatal accidents where pilots shut down the engine(s) and tried to glide to the runway—and overshot or undershot. The reason? First, an engine out landing is an emergency—trying to solve one emergency by creating another ranks way up there on the stupid scale and may just make you a candidate for a Darwin Award. Second, none of the pilots had practiced engine out glides within the last six months. Third, none of the pilots had ever tried to shut down an engine, stop the prop and glide to a landing. We pilots do pretty well at complicated stuff that we’ve practiced. The first time we try a complicated something we haven’t practiced—especially with some stress in the mix—we don’t do well at all.

The odds of you landing safely gear up are extraordinarily good if you don’t do something other than make a normal landing.

You also increase the odds of a good result if you land on pavement rather than grass. NASA full-scale crash tests in the early 1970s showed that a touchdown on grass or dirt with some degree of descent rate—such as after a stall—would stop the airplane in a matter of inches as the ground gave a little and then formed a crater or berm and brought the airplane to a sudden stop. The same impact on pavement turned into a long slide and was survivable. So, if you do err on a gear-up landing and stall the airplane a few feet above the ground, it won’t be a big deal on pavement but you could be the first injury or death in a gear-up landing if you try it on an unpaved surface.

I pulled my notes together and went over to refill and start the coffee maker. A few moments later, Karver and Kary walked into the room pretty pumped up after their flight. They’d had a chance to shoot a couple of approaches to minimums before the clouds broke up. After Karver poured himself a cup of coffee, he saw that I was still in the lounge and had some paper in front of me. “Hey, Dude, did you really get some stuff on forced landings?” He looked a little surprised as he walked toward me.

I gestured at the papers, “Sure, it’s right here. And it turns out that it boils down to using shoulder harnesses, touching down as slowly as possible without stalling, flying the airplane all the way into the crash . . .”

Rick Durden is a CFII and holds an ATP with type ratings in the Douglas DC-3 and Cessna Citation. He is the author of The Thinking Pilot’s Flight Manual or, How to Survive Flying Little Airplanes and Have a Ball Doing It, Vols. 1 & 2.