A number of non-cold rolled bolts were installed on PT6A-67 series engines during manufacture and overhaul
Once cold rolling identified as a problem, SBs issued to phase out non-cold rolled bolts that may be in service. Also have looked a process with regards to acceptance of critical components and have implemente procedures to increase quality assurance of these components.
Following the discovery that the bolts had not been cold rolled at the head-to-shank fillet radius; the engine manufacturer issued two service bulletins (P&WC S.B. No. 14444 and P&WC S.B. No. 14446) which specified replacement of the first stage carrier bolts.
The service bulletins allowed for scheduled replacement of the affected bolts, with components that had a JB or an X stamped on the bolt head, i.e., bolts that had undergone cold rolling. The engine manufacturer’s field representatives contact all operators of PT6A-67, with one engine found under the 400 hour limit specified in the SB, which required removal within two months. That engine has been removed from service for rectification.
Additionally, the engine manufacturer conducted a value stream mapping (VSM) exercise to review all standard parts used in their engines to identify any parts used in critical areas of the engine. These parts would be considered to be critical parts themselves and be given a 3 million part number (requires part to be designed and inspected to the engine manufacturer’s specifications). The engine manufacturer believes this will help to ensure quality assurance and minimise the risk of non conforming parts.
The ATSB considers that the safety actions taken by the engine manufacturer adequately addresses the safety issues identified during the investigation.
