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ACRO E-mail Archive Thread: S2B Longerons

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ACRO E-mail Archive Thread: S2B Longerons


Thread: S2B Longerons

Message: S2B Longerons

Follow-Up To: ACRO Email list (for List Members only)

From: Dave Swartz <dswartz at>

Date: Sat, 11 May 1996 00:16:16 UTC


I fly one of the three 1991 S2B's that broke -  I was flying it when the longerons let loose.  I made a lengthy post about it some months ago.  The short story is (at least my interpretation) that only 1991 S2B's  with 700 or 800 hours have exhibited the problem up to this point (I do know of one S2S flown in airshows - doing multiple snaps on a 45 down line - that broke.  I also know of multiple S1 aircraft that have broken while flying unlimited).  The 25 hour inspections with the mandatory report will hopefully bring in significantly more information.  The third 1991 S2B with a broken longeron was found only because the pilot was aware of the two prior incidents and he decided a detailed inspection was in order (before Aviat or the FAA ordered it).  My personal concern has been that there is the potential that improper heat treatment of these welds lead to weakened metal just aft of the weld.  The breaks on my aircraft were consistent with such a failure according to 2 welders that saw the breaks -  this does not necessarily mean thats how they were broken.  When I was the only one to break a longeron, most people were of the opinion that I must have overstressed it (I did not).  Now that two others have broken in exactly the same way with about the same number of hours the debate can start up again.  The other S2B that broke in flight was damaged severely enough that the NTSB cut the cluster out of the aircraft for metallurgy tests - I have not seen the final results.  I had an aileron bracket fail just aft of its weld 2 months after the longeron incident.  I gave the bracket to the NTSB for testing - the final NTSB report for the bracket failure lists manufacturing defect in welding as the cause.  This shows that some bad welding was being done at Aviat at the time of at least my aileron brackets manufacture.  S2Bs have been built for 13 years, I do not believe that the 3 broken aircraft had the same strength as those that were built in the many years before.  I don't know how many S2Bs have accumulated 700 hours, but there must be several that have been used commercially and in airshows.  I would have expected one to break before mine.


© Dr. Günther Eichhorn
Email Guenther Eichhorn