Bell 206L-3 N708M incident near Abilene, Texas

Probable cause

The formation and propagation of a fatigue crack in the trailing edge of the main rotor blade due to interconnected porosity and resultant corrosion. The area of interconnected porosity was due to a manufacturing defect which was not detected during the manufacturing process.

NTSB analysis

Following the post-flight inspection of a repositioning flight, the pilot noted a crack in the trailing edge of the rotor blade. He had characterized the previous flight as turbulent, but otherwise unremarkable and without any mechanical anomalies. An examination of the main rotor blade revealed a path of interconnected porosity between the lower trailing edge skin, trailing edge strip, and epoxy that allowed for the introduction of moisture and resultant corrosion. The failure was due to insufficient squeeze-out of the epoxy layer between the lower skin and the trailing edge strip during manufacture. The corrosion pit allowed the formation of a fatigue crack with a resultant crack along the blade surface.

Text from the NTSB. Open the NTSB docket for CEN09IA234 for the full record.