Bell 206 N395AE accident near Dublin, Georgia

Probable cause

A partial loss of engine power on takeoff due to separation of the diffuser assembly as a result of incomplete braze joint surfaces on the vane airfoils.

NTSB analysis

The pilot said that he heard a noise from the engine deck followed by a "clicking" noise as he was starting to accelerate the helicopter forward on takeoff. The helicopter immediately began to descend then impacted the ground and bounced before coming to rest upright. The main rotor blades flexed and severed the vertical stabilizer. Examination of the engine's compressor section revealed the diffuser had separated into two sections, exposing the vanes. The diffuser is comprised of individual vanes that are brazed between two annular plates and a third support ring to form one solid diffuser assembly. Metallurgical examination of the separated plate and ring section revealed that the ring section separated through the braze joint at the forward interfaces of the vanes due to a large amount of incomplete braze joint surfaces on the vane airfoils.

The vane assembly was marked with a Federal Aviation Administration parts manufacturing approval number. A search of the manufacturing history of the diffuser revealed that the part was sold to a turbine engine overhaul company about 13 years before the accident. The diffuser, which was zero-timed, was installed in the compressor and sent to the operator. A review of the engine logbook revealed that the diffuser had not been removed/repaired since it was installed on that date and that it had accrued a total of 5,763.1 hours at the time it failed. According to the company that sold the diffuser to the overhauler, any manufacturing history on the diffuser was no longer available due to the company’s 10-year retention policy for manufacturing records.

Text from the NTSB. Open the NTSB docket for ERA19LA152 for the full record.