US announces review of Boeing Dreamliner
January 11, 2013 Leave a comment
http://www.cnn.com/2013/01/11/travel/dreamliner-problems/index.html?c=mobile-homepage-t Safety reviews are more of a politician CYA thing than a scientific process in this kind of situation. There is no ground based simulator that can simulate the effects of one year, let alone ten or twenty years, of exposure to elements, low pressure and changing pressures, freezing and thawing, jarring pressures from landing, wind and turbulence, etc. Putting planes with new materials in the air with people on board under regular conditions for long periods of use is part of the scientific process. You can’t hit a fast forward button and skip that phase of the experiment. The experimental stage of plane development can’t be completed in a lab or even with lots of test flights. It’s economically impossible to put thousands of planes in the air with potato sacks in the passenger seats for ten years of regular travel to and from various combinations of airports. It would cost at least hundreds of billions of dollars. No airplane manufacturor would ever design a new plane again if they had to do that. At some point they have to put people in the sky and wait and see if anything falls out of the sky. There are all sorts of things you can’t reproduce in a lab or in field experiments, including a lower diligence environment. When testing a new plane you probably wheel it back into the hanger when it’s done for the day. You probably keep it above freezing when it is on the ground and it isn’t in use. The plane is probably serviced and each part meticulously oiled or cared for ten times as much as will happen in regular sevice. If you are the development team you want everything to be perfect. The plane is your baby and you will be concerned for the safety of the test flight crews. Day to day service is going to be different. Regular ground crews will have different priorities, like economics and flight schedules, time pressures and occasionally poor weather conditions. They may give new planes extra respect for a while but eventually they will see them as just like any other plane. Over the years problems will start to develop. With new materials you may have new problems. They may never appear in lab or test flight conditions. The most famous example is the older planes that had square windows. Eventually they began disintegrating in mid-air and nobody knew why. Eventually people figured out that square windows led to stresses at the corners resulting in hull failure and explosive decompression. And that is why planes don’t have square windows anymore. Nobody knows what the next “square windows” issue is going to be. When we find it it may seem obvious in retrospect but that shouldn’t be taken as a sign of negligence. Everything seems obvious in retrospect- when you have the data that you didn’t have before. The one thing I would be critical about is higher cabin pressures. The new materials are stronger and that has been used to justify higher cabin pressures. Higher cabin pressures are better for flyer health and comfort and are in the long run desireable, provided that they don’t affect flyer safety. The first years of an entirely new plane design are inherently, unavoidably experimental. Changing an additional important variable, in a direction that tends to increase risk, is a questionable decision. One of the major stresses on a plane is the difference in pressure between the air inside and the air outside. It may accelerate the aging of the structure of a plane if cabin pressure is increased. Note that one of the recent problems on the dreamliner was a cracked windshield. Increased cabin pressure increases the chance that a potentially serious defect like that leads to explosive decompression. If there is windshield failure and decompression in a plane in the cockpit, with air coming in at those speeds, that isn’t a survivable event for most on board. One thing that manufacturors probably should do is periodically swap out new planes for old ones and take older planes apart and see where they seem to be developing wear. Essentially do a post crash reconstruction on a plane that hasn’t crashed. Do x-rays or whatever scanning would reveal unseen stresses or warps. Test plasticity and elasticity in parts to see if anything is becoming more brittle. One thing that may be an issue is what happens to things with carbon structures that get left out in the sun. Planes get lots more solar radiation because they go up where there is less atmospheric protection. The new planes are apparently mostly carbon. I would be thinking about what happens when you cook it. Maybe that’s a non issue but it may be a real issue. Even very small, incremental changes over time can add up to a problem. So where does the press fit into all of this? When I see reports of various different problems and some government agency stating that it is going to “review” the dreamliner I have to be suspicious of motives. What is likely to be a common cause of an engine leaking oil and a windshield cracking? It looks like a publicity oriented wank. It may unnecessarily undermine the brand, so later when there is some unrelated problem with say the tail that leads to a crash we’ll hear some broad sweeping statements from the press and political institutions like “we always knew there were problems with that plane”. The few thinking people out there will then be thinking, you always knew that there were problems with the tail because of a cracked windshield and a leaky engine? Explain that intellectual process. For everybody else it will look like some big cover-up. What is the point of regulation through the media? It may advance rivals like Airbus. It may be used for bargaining down Boeing on new planes. It may be used as a pretext to cancel orders. What is a “review” of e.g. a cracked windshield going to be? You have a sample size of one. Unless it suggests something specific to look for in other planes it ends there. It will probably not elaborate the separate engine leak in any way. And until examination is done there isn’t anything to announce to the public. So why did US regulators just throw Boeing under a bus to grab headlines?
stciappelletto 