NTSB Identification: MIA97LA099.
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Accident occurred Tuesday, March 11, 1997 in LABELLE, FL
Probable Cause Approval Date: 04/10/1998
Aircraft: Bell UH-1B, registration: N70696
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.
A main rotor blade had been changed during troubleshooting of the main rotor system. While in a hover to track and balance the rotor system, the other main rotor blade and grip separated. Examination showed the main rotor blade and grip separated due to fatigue cracking of 40 out of 49 main blade strap laminates. The blade that had been change and did not separate was found to have 26 out of 49 main blade strap laminates separated due to fatigue. The fatigue initiated at the strap pin hole. The main blade straps have a life limit of 1,200 flight hours. Logbook records showed the main blade straps were installed in the rotor hub assembly during overhaul in Singapore, 640.4 flight hours before failure. The main rotor straps were reported to be new when installed.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: Company maintenance personnel's failure to properly evaluate a main rotor system problem resulting in main rotor straps with multiple laminates separated due to fatigue cracking being allowed to continue in service until failure and separation of a main rotor blade. Full narrative available
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