Accident Sequence
The pilot was applying pesticide to a cotton field when the outboard 9 feet of one main rotor blade separated in flight. The separation caused the entire main rotor system to detach from the main transmission mast.
Blade Damage and Repair History
Investigation revealed that the blade separation resulted from fatigue cracks that emanated from a puncture through the lower surface in the leading edge area. The shape of the puncture, a crater mark above it, and heavy lead residue indicated that a bullet had entered the blade. The puncture had been repaired; however, manufacturer's specifications stated that this type of damage is nonrepairable and the blade should have been scrapped.
Prior Inspections
In July 1995, the rotor blade was modified, and during that process it was inspected for damage. In April 1997, an airworthiness directive requiring inspection of the blade was complied with. Despite these inspections, the preexisting bullet damage and repair were not identified or addressed per manufacturer guidelines.