The nut manufacturer’s production control and quality control processes failed to prevent the release of one or more lots of MS21042L-4 nuts that remained in a partially-embrittled state after cadmium electroplating.
The nut manufacturer’s Technical Quality Notice Bulletin demonstrates a level of understanding of the issues that should be sufficient to ensure that the risks of future hydrogen embrittlement of the MS21042L-series nut and related products are minimised. Nevertheless, given the widespread use of this nut type across a variety of aviation and aerospace applications, the ATSB will continue to monitor reported safety occurrences and service difficulty events for any further indication of nut embrittlement issues.
On 4 April 2012, Airfasco Industries issued a Technical Quality Notice Bulletin covering MS 21042 Thin-Wall Hex-Flange Nuts. The bulletin listed six specific issues relating to the structural integrity of the nut type, including several new measures to more effectively manage the risk of product remaining in the embrittled or partially-embrittled state upon release. Although Airfasco has designed an alternative ‘hydrogen embrittlement negative (HEN)’ thermal diffusion coating for MS21042/NAS1291nuts, replacing the cadmium electroplated finish, this is not yet specified in NASM21042. This bulletin was subsequently revised and re-issued on July 16, 2012.
The ATSB is satisfied that the actions taken by the above organisation should reduce the risk of future manufacturing deficiencies with the MS21042L-series nut product.
