Aircraft and Flight
The aircraft involved was a Piper PA-22 that had been converted to a PA-20 under STC SA45AM. It was being used to provide a biennial flight review for the owner-pilot, who was considered the pilot in command on that flight.
Accident Sequence
During the flight, the right wing folded back over the fuselage and the aircraft crashed.
Examination of Wreckage
An examination of the wreckage revealed that the forward lift strut for the right wing had failed in an area of severe corrosion. The failure occurred at the lower part of the lift strut near the fuselage attachment point.
Maintenance History
Review of the annual inspection checklist indicated that all applicable airworthiness directives (ADs) were complied with as of July 21, 1989, and that the lift struts were visually inspected at that annual inspection. The aircraft logbook showed that AD 77-03-08, which requires mechanical testing of the lift strut for evidence of corrosion at five-year intervals, had been complied with in July 1988.
The aroma of linseed oil was noted in all lift struts, but polymerized linseed oil was found in the right and left rear struts. Internal corrosion had perforated the right forward lift strut prior to its failure.