Amateur-built EXEC 162F N6828D accident near Mt. Comfort, Indiana

Probable cause

The pilot’s installation of an unauthorized main rotor belt and his subsequent failure to properly inspect the belt, which resulted in inadequate belt tension, the belt’s failure, and the subsequent loss of engine power.

NTSB analysis

The pilot reported that, while the experimental, amateur-built helicopter was climbing through 300 feet, he heard a loud "bang" come from the rear compartment and that the helicopter subsequently yawed right. He made an emergency autorotation landing to a field. During the landing, the helicopter's skids sunk into the mud, and the main rotor blades contacted the ground. The helicopter then came to rest on its side. A postaccident examination of the helicopter revealed that the main rotor belt was not approved for aircraft use and that it was broken straight across in a crimp-type failure. According to the belt manufacturer, belt crimping damage is "commonly associated with belt mishandling, inadequate belt installation tension, sub-minimal sprocket diameters, and/or entry of foreign objects within the belt drive." No foreign object preimpact damage was found. Further, although the belt was an unapproved part, it should have been inspected during each 25-hour standard inspection and the belt tension was to be tested during each annual inspection. At the time of the accident, the belt had accumulated 215.9 total hours. Based on this evidence, the pilot installed an unauthorized main rotor drive belt and then failed to properly inspect the belt, which resulted in inadequate belt tension, the belt's failure, and the subsequent loss of engine power.

Text from the NTSB. Open the NTSB docket for CEN14LA307 for the full record.