William.
When doing research, come to the right conclusions. Don't stop reading the preliminary report of an NTSB record -read the full narrative. In your first cited accident the first conclusion was wing spar failure due to corrosion. It was a too fast conclusion and it is IMHO a mistake that the NTSB records are not being updated with the true facts. The thorough examination of the wing spar found a different picture. >From the full narrative of that accident: http://www.ntsb.gov/NTSB/brief2.asp?ev_id=20040315X00324&ntsbno=LAX04FA150&akey=1 "A National Transportation Safety Board senior metallurgist examined the two fractured portions of the front spar from the center section of the wing. The spar fractured approximately along the centerline of the fuselage. The fracture extended through the upper and lower caps and the web portion. The total length of the two fractured spar pieces measured 51 inches. Visual examination of the front spar revealed the upper and lower spar caps and webs contained mating fractures. The mating fractures for the upper spar cap were placed next to each other and visually examined. The upper spar cap portion adjacent to the fracture exhibited bending deformation consistent with the outboard ends of the spar cap bending upward relative to the spar. The upper spar cap was deformed slightly forward relative to the position of the lower spar cap and the upper portion of the web also was bent forward. Further to the left of the fracture location, the upper spar cap contained bending deformation that was in the opposite direction to that associated with the fracture. The web portion in the center section between the upper and lower spar cap contained buckling deformation from excessive loading in the vertical direction. The web portion contained fractures on a plane of 45 degrees relative to the length of the web that is typical of an overstress separation. The web of the wing spar is riveted to vertical flanges on the upper and lower spar caps. Twenty rivets between the web and upper cap flanges were found fractured, allowing this portion of the web to separate from the upper cap. Remnants of the fractured rivets remained attached to the upper spar cap, but the head portions of these rivets were missing. The 20 rivets fractured at the shank portion near the transition between the shank and head. The fractured rivets were firmly in place and the exposed portions of the rivet heads and tails showed no evidence of degradation from corrosion. One of the rivet faces was examined using a scanning electron microscope and showed intergranular features consistent with stress corrosion cracking in aluminum alloy. An ultrasonic inspection of several of the intact and fractured rivets did not indicate that any of the intact rivets were cracked." So clearly, this airplane came down due to overstress NOT corrosion!. Second example is N3330H that had a corroded trailing rib in the center section. A few other Airplanes have experienced the failure of this rib on either side. These ribs are non critical for flying forces albeit structural. Since N3330H is in my possession and also was when the rib had been replaced, I can state that until the center section AD these ribs had been out of awareness and corrosion here could go undetected. This has been changed due to the 3 year recurring AD that makes you examine all parts of the center section. Your last example is of the Aircoupe BKIN which suffered corrosion bad enough that it probably was uneconomic to be repaired. This was true for many Ercoupes. And this leads me to the conclusion your research probably did too. One should carefully examine an Ercoupe prior to purchase. What I would not dare to tell our fellow Ercoupers is that some of them should not fly their unrepairable rust buckets. Our birds are having recurring ADs that ensure the examination of the whole wing and center structure on a regular basis. I remove the inspection panels every 12 month and I make sure that every sign of corrosion will be taken care off. I am positive that many Ercoupers on this list are as careful as I am. In this regard is is not helping us to be lectured about unsafe airplanes and potential dangers. After all, until now no Ercoupe fell out of the sky due to corrosion. Key is here that corrosion always had been detected and remedied either way before a structural failure occurred. The Ercoupes that were uneconomical to repair experienced most likely exfoliation corrosion of one of the center spar caps. A new center spar is running over $10 k from Univair and is very labor intense to replace. You can run easily into $15K when trying to replace one. These planes are to avoid. This is the answer to the question you did not ask. Hartmut To: [email protected] From: [email protected] Date: Mon, 25 May 2009 22:45:34 +0000 Subject: [ercoupe-tech] Corrosion: Elephant in the Living Room? I've searched for a suitable Ercoupe continually for the last 6 weeks and I'm an ace Google researcher. One theme that is leaping out at me is CORROSION. As an unbiased newcomer, I can clearly see corrosion is the proverbial elephant in the Ercoupe living room. This infamous NTSB accident finding speaks volumes: http://www.ntsb.gov/NTSB/brief.asp?ev_id=20040315X00324&key=1 The key statement is: "Comparison of the inspection requirements in the Service Bulletins and AD's to the area where the corrosion was present in the accident aircraft revealed that none of the inspection methods would likely have found the corrosion." The response to this blunt warning is varied: some have exercised due diligence and performed invasive evaluations of their airframes, including skin removal, ultrasound, and scraping if required; while others have chosen to focus on the Red Herring aerobatic component of the accident report. The vivid pictures in this well known submission are stunning: http://www.ercoupe.info/?n=Main.Hartmutscsection Key statement: "I found some surface corrosion on all parts where previous primer applications did not reach. Nothing major. It just needs a cleanup and prime and done. Then I found what we all are afraid of, something which looked like corrosion on the inboard spar of the trailing edge on the right side of the center section. It is hard to see, because one has to look through two lightening holes, with the wings detached, And even then you can see just a fraction of the rib." The corrosion in this account almost went undetected except for the due diligence of the owner. Corrosion even went undetected during the refurbishment of G-BKIN: http://www.popularaviation.com/Ercoupe/PhotoGallery.asp?Page=6 Key statement: "Shortly after this photo was taken G-BKIN was shipped to the States to Seattle (Tacoma) rebuilt and flown there for a short time before being scrapped due to corrosion in the center section AD." The airframe was "rebuilt and flown" prior to detection of corrosion requiring scrapping. The important thing I've learned in all this is: SERIOUS CORROSION OFTEN WAS YEARS IN DEVELOPING AND WENT UNDETECTD DURING NUMEROUS ANNUAL INSPECTIONS AND EVEN REFURBISHMENT. I personally will exercise extreme caution in my Ercoupe search and insist on rigorous assurance that a prospective airframe is safe. The Ercoupe is an endearing aviation classic. It has both a trendy retro-modern look and a technical execution that remains competitive in the 21st Century. Unfortunately, it is those virtues that belie it's extreme age and possible hidden weaknesses. In my less than humble opinion, it is likely some operational Ercoupes should not be flying, and for some of those, the price of remediation is unacceptable. These are old airplanes, the numbers are dwindling, and the task of finding a safe and reasonably priced airframe is difficult. _________________________________________________________________ Windows Live™: Keep your life in sync. http://windowslive.com/explore?ocid=TXT_TAGLM_BR_life_in_synch_052009
