Over the next week or 10 days, I’ll be writing a few blogs on aviation risk assessment—how people judge it and how they mitigate it. While I’m getting started on that, a reader wrote to challenge my assessment of the J-3 Cub’s safety and crashworthiness. I touched on this in the Aviation Consumer article that was a companion piece to the AVweb video.
In that article, I had made this point:”By modern standards, both the Cub and Champ have an appallingly unsafe fuel tank location. (Remember, it was the 1940s.) It’s inside the cabin, behind the firewall and immediately in front of the front seat occupant.” Worth noting is that many Champs have been modified with newer wings that put the tanks in the wings and some Cubs have both wing and fuselage tanks.
Either way, a reader sent us this comment: “I must take issue with your statement … I believe that this is a statement of opinion which is not supported with either test or statistical data. Although it may seem intuitive to make this statement, there are actually many factors to be considered in the design of a crashworthy fuel system. Tank location is only one of those; and not necessarily the most important. I’m also fairly certain that neither Piper or Aeronca considered any of the factors, but that doesn’t mean the system is unsafe; until proven otherwise. You do a disservice to readers by implying that a system is unsafe when, in fact, you have no data to support that.”
This comment, a fair criticism, actually, raises a perennial conundrum: How can you tell the difference between intrinsic or inherent lack of safety and demonstrated lack of safety? Intrinsic means it looks unsafe, demonstrated means that it has actually been shown to be. As the reader rightly points out, just because something looks unsafe, doesn’t mean that it is. The best way to sort through the clutter is to gather some actual data, something that can be hard to come by.
When I wrote that comment, I was basing it on the memory of a research project I did around 2000 on vintage taildragger safety. I knew the J-3 Cub had a pretty poor showing, but I didn’t have the numbers at my fingertips. So I spent a couple of hours digging it up and it turned out to be a little worse than I recalled. Between 1970 and 2013, I found 24 fatal accidents involving the J-3. Of those, 14 or 58 percent had post-crash fires. There may be models with a worse history of post-crash fire than that, but I can’t recall any. Of course, the negative test is this: Would the fire issue be better or worse with wing tanks? One way to test that is to look at the PA-18 Super Cub, whose tanks are in the wings, albeit with small header tanks inside the cabin. Otherwise, the two airframes are functionally comparable. A quick scan of 39 Super Cub fatals revealed that 17 or 43 percent had post-crash fires.
That’s a little better than the J-3, but I might be tempted to say rather than being better than the J-3, it’s almost as bad. In any case, because of the Super Cub’s popularity as a floatplane, many of its fatal crashes are in lakes, which obviously tends to suppress post-crash fire. In my view, neither of these airplanes have a laudable record for not burning after a crash. You can ring the changes on the data by considering all accidents rather than just fatals, but the outcome is similar. For comparison, for newer airplanes, post-crash fire rates are in the 20 to 30 percent range. Some are much lower than that.
Two important principles of crashworthiness are to keep the fuel out of the cabin as much as possible and protect tanks and lines from breach by crash forces. When the Cub was designed, less was known about crashworthiness and I suspect it wasn’t much of a priority anyway. But today it is and it can be done. Diamond Aircraft, for example, has the lowest incident of post-crash fire in the industry. It’s functionally near zero. They’ve done that by protecting the tanks and armoring the fuel lines. Some LSA manufacturers are putting tanks inside the cabin or fuselage, but they are often armored in Kevlar or constructed of heavy, puncture-resistant plastic.
The Cub, by contrast, has a thin-walled aluminum tank with an exposed gravity line from the tank bottom to the carburetor just inches from the front passenger’s feet. The tank is literally in the lap of the front seat occupant. The Cub has nothing like a crush zone, but if it did, the tank is right in the middle of it. We don’t have much data about crash forces and their consequences for airplanes like the Cub, but we do have outcomes. If an aircraft burns in almost two-thirds of its fatal crashes, that’s pretty good evidence, in my estimation, that the fuel is not well-protected. Is it unfair to judge a 77-year-old airplane by modern standards? Surely it is. But it’s equally unfair—in fact irresponsible—not to point out an old airplane’s warts, just because you happen to like the thing.
Hey, Watch This!
And while we’re on the subject of intrinsic versus demonstrated risk, the confluence of unforeseen technologies has given us a new twist, specifically YouTube and the GoPro camera. This has created a vaporously thin membrane between YouTube stardom and a galactically creative Darwin Award winner.
Check out this video, which appeared a couple of weeks ago, in which Erik Roner, described as a “GoPro athlete,” reprises Larry Walters’ famous 1982 trick of tying a bunch of helium balloons to a lawn chair and ascending into the blue. But Roner upped the ante in two ways. First, he filmed the flight with what looks like about six GoPros and rather than a pellet gun to dispatch the balloons to control his altitude, he brought along a pump shotgun. And while Walters actually landed his balloon, tanking some powerlines and causing a blackout in the process, Roner bailed out of his rig, descending under his parachute over uninhabited range territory.
What happened to the shotgun? Oh, he held on to it in freefall, ditching it at the last minute by unceremoniously dumping it in the dirt from 50 feet. Looks like he kept the canopy in brakes until that point so he’d have two hands free. One three-second clip I missed was the one showing how he very carefully cleared the chamber before jettisoning the weapon and thus proving he wasn’t going to get peppered with his own shot or otherwise blow a part off. He would have done that, I’m sure. Right? (I’m real big on firearm safety.)
This was obviously a carefully planned stunt by the looks of it. But I sometimes wonder what sort discussions GoPro has about encouraging—or not—ever more extreme stunts, especially aviation-related ones, until someone punches right through the membrane into full-flight Darwinism. At least if they do, it will be well-documented for our edification and entertainment. And really, in the modern era, isn’t that what it’s all about?
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