The Society of Automotive Engineers specification AS7477 was ambiguous in relation to the requirement to cold roll the head-to-shank fillet radius of MS9490-34 bolts.
SAE reviewed standard and implemented changes to the wording
The engine manufacturer reported that it had advised SAE International standards division committee SAE E-25 of the possibly ambiguous wording of sections of SAE International specification AS7477 in respect of the requirement to cold roll the under head fillet radius.
The engine manufacturer further advised that committee SAE E-25 had unanimously agreed that specification AS7477 bolts required cold rolling of the under head fillet radius, and that the standard required revision to provide a clearer set of requirements in that regard. Revision E was issued by the SAE in October 2011, and expressly stated that the fillet shall be cold rolled, even if there is no evidence of grinding or tool marks.
The ATSB considers that those safety actions proposed by the engine manufacturer will address the safety issues identified during the investigation.
