Aviation safety issues and actions

Production release of partially-embrittled MS21042L-4 nuts

Issue number: AO-2011-135-SI-01
Who it affects: All owners and operators of aircraft using MS21042 and related nuts
Issue owner: Airfasco Industries Fastener Group
Transport function: Aviation: Air transport
Background: Investigation Report AO-2011-135
Issue release date: 22 January 2014
Current issue status: Adequately addressed
Issue status justification:

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.

Safety issue description

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.

Proactive Action

Action organisation: Airfasco Industries Fastener Group
Date: 22 January 2014
Action status: Closed

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.

ATSB comment:

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.

Last update 22 January 2014