Bell 206L-1 N37AE accident near Greensburg, Indiana

Probable cause

The in-flight separation of a main rotor blade due to a fatigue failure of the blade spar, rendering the helicopter uncontrollable, and the manufacturer's production of main rotor blades with latent manufacturing defects, which precipitated the fatigue failure of the blade spar.

NTSB analysis

The emergency medical services crew had attended a local fundraising event and was returning to the helicopter/crew base when the accident occurred. Witnesses reported that the helicopter made a normal departure. They subsequently reported seeing components separate from the helicopter before it descended and impacted the ground. The helicopter came to rest in a corn field approximately 1.2 miles from the departure point. A postaccident examination of the helicopter revealed that an 8-foot section of one of the main rotor blades separated in-flight rendering the helicopter uncontrollable. Metallurgical examination determined that the blade failed as a result of fatigue cracking. The origin of the fatigue crack coincided with a large void between the blade spar and an internal lead weight. Further investigation determined that the presence of residual stresses in the spar from the manufacturing process, in combination with excessive voids between the spar and the lead weight, likely resulted in the fatigue failure of the blade. The manufacturer issued an alert service bulletin that identified main rotor blades that may have been affected by the combination of residual stresses and excessive voids between the spar and the lead weight. The service bulletin also called for supplemental inspections in order to maintain the continued airworthiness of the affected blades.

Text from the NTSB. Open the NTSB docket for CHI08FA269 for the full record.