Bell 430 N430ST accident near Kailua, Hawaii

Probable cause

The separation of one of the tail rotors blades’ root enclosures due to improper repair.

NTSB analysis

The pilot of the sightseeing helicopter flight reported that he experienced a loud thump immediately followed by vibration and that he chose to conduct a precautionary landing at a nearby airport. Postaccident examination of the tail rotor components revealed that one of the tail rotor blades’ root enclosures, along with its associated weights and attachment bolts, had separated. The other tail rotor blade sustained a 6-inch-long dent about mid-span when the root enclosure separated.

About 200 flight hours before the accident, the subject tail rotor blade was removed from service due to a delamination of the root enclosure at the root block and a repair was made of the blade’s root enclosure area. Scratches were observed on the root block around the edge of one of the tail rotor blades’ root enclosure areas, consistent with surface preparation for the repair. However, while the surface preparation with the scratches created an appropriate bonding surface, the adhesive did not properly bond to the remaining area of the faying surface due to corrosion.

Additionally, no adhesive was applied into the gap between the root enclosure and root block. This action would require the surface in that area to be prepped for the application of the adhesive, and no evidence of such preparation was observed. The surface of the root block to where the enclosure was bonded was corroded with paths of oxidation extending outboard, consistent with trapped moisture between the adhesive and the enclosure, which eventually resulted in the enclosure separating from the root block.

Text from the NTSB. Open the NTSB docket for WPR19LA028 for the full record.