NTSB Identification: CHI96FA185.
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Accident occurred Monday, June 03, 1996 in LAPEER, MI
Probable Cause Approval Date: 08/25/1997
Aircraft: Corey CIRRUS VK-30, registration: N7033G
Injuries: 1 Fatal.
NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.
According to witnesses, the accident pilot reported on Unicom that his 'flap bracket had broken.' A pilot who was on the ground near the accident site reported that he observed a 'violent flutter' on the right wing. Examination of the right flap revealed the inboard flap push rod was fractured at the end cap. The push rod welds exhibited 'porosity and secondary cracking indicative of poor welding techniques.' The inboard cruise flap push rod 'exhibited a thumbnail crack, which may have indicated failure by high stress, low cycle fatigue.' The outboard cruise flap hinge was fractured. Examination revealed the hinge was constructed entirely of composite material. The kit manufacturers drawings specify an aluminum core for the hinge. Differential scanning calorimetric analysis of the composite cruise flap skin revealed the vinyl ester matrix material was 'not fully cured.'
The National Transportation Safety Board determines the probable cause(s) of this accident to be: incomplete cure of the bonding material in the cruise flap, improper material in the cruise flap hinge, and improper welding of the cruise flap push rod end caps. Factors were delamination of the cruise flap, partial failure of the cruise flap hinge, and fatigue failure of the outboard cruise flap push rod. Full narrative available
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