Recommendation

CASA will review MAF Aviation Services Engineering Order
0071-001 El and the cadmium plating and baking process controls
employed by the plating subcontractor. The Authority undertakes to
provide the Bureau with details of the review once completed.

CASA contacted MAF and reviewed Aviation Services Engineering Order 0071-001 E1 and the cadmium plating and baking process controls employed by the plating subcontractor. The following points provide a summary of that review.

• The MAF Engineering Order (EO) has called up cadmium plating in accordance with the established standard QQ-P-416, now referred to as SAE-AMS-QQ-P 416.
• MAF Interpretation of the QQ-P-416, resulted in it not requiring the stress relief treatment prior to plating (QQ-P-416 3.2.2) and was therefore not performed on the affected nuts. The MAF interpretation was based on these items not being new (ie. not newly manufactured as specified in QQ-P-416), hence not requiring the stress relief process.
• The MAF EO required hydrogen embrittlement relief treatment in accordance with QQ-P-416 after plating, 150 KSI and above.
• MAF amended the EQ and deleted the cadmium plating approval for the affected nut in March 2004 (post the failed incident).
• MAF further amended the EO and required all parts listed in the EO be stress relieved prior to plating. Additionally, the Order also required hydrogen embrittlement relief after plating.
• MAF has advised CASA that they now only use new nuts (P/N 652541) on the engines.
• MAF does not consider the use and/or location of the standard hardware under consideration for cadmium plating.

However, the organisation has evaluated the cadmium plating type, class, strength and process for each item under consideration for plating approval.

CASA was unable to determine if performing the pre-plating stress relief process resulted in a failure on this occasion.

The ATSB's report implies that the failure is more consistent with no hydrogen embrittlement treatment post plating, which was required by the MAF EQ.

I am advised that during the forthcoming audit of MAF, CASA intends to discuss this issue further with the relevant MAF design persons.

It should also be noted that an article on the aspects of cadmium plating and hydrogen-induced embrittlement is planned for the upcoming edition of Flight Safety Australia.