Incident Overview
During a demonstration flight intended for a potential buyer, witnesses at the airport observed the aircraft's right wing fold rearward immediately after takeoff. The aircraft then descended in an uncontrolled manner.
Investigation Findings
Examination determined that the right wing forward lift strut had separated from its lower fuselage attachment clevis bolt. Metallurgical analysis of the lift strut's threaded barrel revealed that the bottom 1-1/4 inch was missing most of its threaded crowns, with the area covered by corrosion residues. The top 3/4 inch of threads were partially deteriorated by corrosion. Furthermore, the entire length of the bolt hole was dry, lacking the linseed oil coating that was present in the threaded holes of other struts, which remained wet.
Maintenance History
The aircraft had been rebuilt by mechanics holding A&E (Airframe and Engine) and A&I (Airframe and Instrument) ratings. An annual inspection had been signed off the day before the accident.