NTSB Identification: MIA96LA176.
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Accident occurred Wednesday, July 03, 1996 in MARATHON, FL
Probable Cause Approval Date: 02/28/1997
Aircraft: Hiller OH-23C, registration: N301CH
Injuries: 2 Minor.
NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.
During a previous flight, the helicopter was reported to have excessive vertical vibration and to require excessive collective forces during flight. Mechanics worked on the main rotor blades to correct the problem, then the helicopter was flown on a maintenance test flight. During the test flight, the pilot noted that the vertical vibration had 'gone away,' but before landing, the vertical vibration returned. Shortly thereafter, the pilot heard a loud 'pop'. As he flared for landing, the blue main rotor blade separated and the helicopter crashed. Examination of the separated blade showed the wood in the area of the blade grip had failed, allowing the blade to separate. Evidence of a previous repair was present in this area, which lacked adequate adhesive between some of the mating surfaces. Also, an unapproved sealant had been used over the repaired area, and oil had contaminated the wood in this area. There was no evidence of dry rot in the failed area. The logbook records did not show the previous blade repair.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: Improper repair of a previous crack in the blue main rotor blade by unknown persons; improper inspection of the main rotor blades by maintenance personnel, following a reported vibration problem; and subsequent failure of the main rotor blade, which resulted in an uncontrolled collision with the terrain. Full narrative available
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