NTSB Identification: CHI94FA140.
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Accident occurred Saturday, April 23, 1994 in WONDERLAKE, IL
Probable Cause Approval Date: 02/14/1995
Aircraft: VAVRA, MARTIN A. REBEL 300, registration: N12MV
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.

A witness to the accident, who was a professional pilot and an aerobatic judge certified by the International Aerobatic Club (IAC), stated the flight originated as a practice aerobatic session. He reported that the right wing folded while the airplane was positively loaded to 6 to 7 G's. Investigation revealed the main wing spar upper cap strip failed in fatigue. Tests disclosed that the strength of the composite carbon fiber material was significantly lower than the design specification due to high porosity, excessive fiber waviness, and low fiber volume.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

FATIGUE AND CATASTROPHIC FAILURE OF THE MAIN WING SPAR RESULTING FROM THE DESIGNER'S EXCESSIVE, UNVERIFIED ESTIMATE OF THE STRENGTH OF THE SPAR CAP MATERIAL AND THE MANUFACTURER'S FAILURE TO ATTAIN THE SPECIFIED STRENGTH DURING THE PRODUCTION PROCESS.

Full narrative available

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