Hi Dave, Congratulations! (I guess)
You appear to have discovered a genuine $11,000 safety-of-flight issue with your spar. I am impressed that Mr. Heagren apparently chose to ignore the regulatory authority tar baby and "cut to the chase" by looking at the situation applicable to your particular coupe. Would you be willing to post the pictures that you showed him? While a load test might show your spar to still be safe, I would not, if your description is accurate, want to fly with it cross-country again and again. On occasion I have encountered turbulence I regarded as significant at or slightly above maneuvering speed. If even one hole penetrates the spar extrusion it is clearly contrary to the factory drawings the FAA has reviewed and found safe. I don't fly with doubt of that potential magnitude. Your unfortunate experience is probably sufficient grounds for Skip to urge every Ercoupe and Forney owner that has bucket seats installed as a "retrofit" (not "factory installed") to have their mechanic carefully inspect whether or not the mounting holes impinge on the spar extrusion. Perhaps Univair would issue a letter to all known owners of record saying the same thing. But there is NO justification whatsoever to issue an AD on the basis of your experience. And, again, non-factory holes in the main spar cap are no less safe than factory holes IF they are drilled in the same location of the same size, pattern and configuration as factory holes. The logic and applicability of the"Boeing 2D rule" to large military or commercial airframes is likely clear, and practical considering such budgets. I would be reluctant to attempt to apply such a rule directly to light aircraft. As the Ercoupe Service Manual points out, private aircraft may look the same and do the same things, but they are much less substantial. They serve less ambitious "missions" for an anticipated service life aloft of many, many less hours; and money from many taxpayers does not underwrite the purchase and ongoing maintenance of each example. Any such comparison is learly one of apples and oranges. To beat a dead horse, while your "discovery" vindicates your prior and premature decision to replace your main spar with a new one, this decision is NO LONGER a reaction or response to the Sebring crash. To the contrary, you have now (with considerable help) identified a genuine airworthiness "issue" in your own aircraft. You have also proved my point that an AD is not necessary for owners to fulfill the responsibilities that the FARs already place on them to keep their aircraft airworthy. It has always been up to individual owners to direct their mechanics to verify that they follow proper procedures, or that said procedures were followed by previous owners. That is as it should be. To such extent as we take that responsibility seriously enough to guide our actions, the FAA should leave us alone. To such extent as an owner might, in a situation such as yours, choose to unload (sell an unsafe coupe to an unsuspecting purchaser) the bird on eBay rather than fix it...how is this different regarding spar holes as opposed to corrosion? Either is morally bankrupt, and more than a few purchasers have had to part out an unsafe coupe bought without a competent pre-purchase inspection. Who did your pre-purchase inspection? ;<) Bob Sanders was fond of saying, "when all else fails, use judgment". No AD says "Use common sense". Perhaps that's because, as Will Rogers observed, "The problem with common sense is that it ain't so common anymore." He also observed that "Some learn from reading. Some learn from watching. The rest have to pee on the electric fence." Words wise, and worth remembering. Regards, WRB -- On Sep 29, 2009, at 19:03, [email protected] wrote: > I just had a nice dinner with my friend Larry Heagren who has been a > career aeronautical engineer at Boeing. He's leaving soon to work > Boeing's end of a contract with the Royal Air Force rebuilding CH-47 > Chinooks. His prior projects include structures on the 767 and 737. > > I brought Larry up to speed on the Main Spar Cap issue and showed him > the engineering diagrams and pictures of unmodified main spar caps and > mine. I explained that we might see some relief for some of the > drilled main spar caps in the form of riveting the holes. Larry > looked at the pictures showing the location of the holes in my main > spar cap and had two observations: > > 1. The line of holes looks like it penetrates the extrusion and does > not go cleanly through the thinnest part of the main spar cap. > > 2. Even if riveting were an approved fix, I don't pass the Boeing > "2D" rule that every engineer knows. Basically take the diameter of > the repair rivet and double it. If you don't have twice the diameter > between the rivet and the edge of the structure, you have to do a full > structural analysis to determine if the repair is safe. > > Larry's botton line was, "You ain't got enough meat between the holes > and the edge of the main spar cap." > > Just a point worth noting if you have non-factory holes in the main > spar cap. > > YMMV, > Dave
