Quality issues/cracking of Spring Washers manufactured by MM&S, USA

Suspected Unapproved Parts Details

Multiple (Standard Parts)
Part name
Spring Washers
Part Number
Serial Number

On 06 February 2018, EASA was notified by LBA of an occurrence report reported by a maintenance organisation regarding suspected unapproved parts used in ATR aircraft passenger windows installation.

The report identified the SUPs as spring washers (P/N BACW10AZ3) used in ATR aircraft but they could have also been installed in other EASA certificated aircraft. During maintenance, the spring washers showed signs of cracking and falling apart when handled.

The spring washers are manufactured in the United States by MM&S, located in Anaheim, California. MM&S holds an FAA Technical Standard Order Authorization (TSOA) for the subject spring washers.

EASA notified FAA and the investigation identified non-conformances with respect to the approved design specification and manufacturing processes. The FAA determined that MM&S did not follow its quality system requirements related to inspection sampling sizes.

FAA has taken appropriate action against the manufacturer and will monitor the manufacturer’s corrective action plan to ensure it is satisfactorily implemented.


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