Accident Summary
During takeoff climb, a loud noise was heard as one of five main rotor blades and the tail boom separated from the helicopter. The helicopter then crashed into a submerged reef approximately 200 feet from the heliport.
Investigation Findings
Examination of the failed main rotor blade showed that its retention strap assembly (RSA), part number 369D21210-501, failed due to fatigue in an area of corrosion. Of the 16 strap laminates, 11 had preexisting cracks. Corrosion was found on 78 of the 80 laminates.
Maintenance History
The maintenance handbook required inspections of the RSA at 25, 100, and 600 hour intervals. Service Information Notice (SIN) DN-77.1 recommended a 300-hour inspection if any crack or laminate failure was found during a 100-hour inspection. Airworthiness Directives 77-15-09R1 and 81-10-08 required inspection within (but not outboard of) the pitch housing.
During 100-hour and AD inspections after 1768 and 1839 hours of operation, up to three cracks were found in laminate legs, but their locations were not documented for subsequent inspections. During two later 100-hour inspections performed by another mechanic, no cracked laminates were noted. The helicopter had accumulated 2135 hours of operation at the time of the accident.
Service Information Letter DL-54 recommended a Tri-Flow wash process after the last flight of each day when operating in a marine environment.