During a maintenance inspection of a Bell 206 helicopter, a main rotor blade bolt nut was observed to be misaligned. The Civil Aviation Safety Authority (CASA) requested technical assistance from the ATSB in the metallurgical examination of parts from the main rotor. To facilitate this assistance, the ATSB initiated an external investigation under the provisions of the Transport Safety Investigation Act 2003.
The ATSB has concluded the metallurgical examination of the main rotor hardware and provided the results of that work to CASA on 6 November 2023. The ATSB concluded that a retention nut to the main rotor blade attachment bolt was almost certainly an unapproved part and that it had been manufactured with off-centre and misaligned features. This has led to excessive clearance when the nut was torqued during final assembly.
CASA is responsible for, and will administer, the release of any information from the ATSB’s examination. Any enquires relating to the matter should be directed to CASA at www.casa.gov.au.