From NTSB Accident Data Base
Accident occurred Sunday, July 9, 1989 at John Day, Oregon, USA
Aircraft: Cushing C2, registration: N129C
Injuries: 1 Serious.
Prior to the pleasure flight, the pilot reported that when assembling the left wing, the mount bolts would not align. The pilot drilled new holes elongating the original holes. The wing was assembled and the pilot attempted a takeoff. Just after lift off, the airplane began to porpoise. Shortly there after, the left wing folded back and up. The airplane rolled inverted to the left and skidded down the runway. Post crash inspection of the airplane revealed that the wing broke away at the spar. Dry rot was noted throughout the entire structure.
The National Transportation Safety Board determines the probable cause(s) of this accident as follows:
The pilot improperly changed the design of the airplane by elongating holes at the wing attachment. The change was not inspected by a qualified individual. As a result of the change, the wing separated at the spar.