The manufacturer’s specified procedure for assembling and torqueing of the crankshaft/propeller flange fasteners was ineffective in ensuring resistance against subsequent joint movement in service.
The documentary changes should ensure the increased reliability of the propeller flange/crankshaft joint and the reduced likelihood of propeller loss due to joint fastener failure.
The manufacturer has issued a revised Propeller Flange Attachment Service Bulletin. It no longer specifies the multi-step torqueing procedure, instead referring to the correct procedure in the Engine Overhaul Manual i.e. single-step torqueing.
An additional requirement has been introduced for mounting surfaces to be free from paint, thread-locking compound or other contaminants before assembly. The relevant painting process specification now requires that all three faying surfaces of the flange be masked plus an illustrative diagram accompanies the text.
