• A cable terminal fitting of the type affected by the CASA mandate. (ATSB)
    A cable terminal fitting of the type affected by the CASA mandate. (ATSB)

The Civil Aviation Safety Authority has introduced mandatory retirement of primary flight control cables made of some stainless steels.

In a Notice of Final Rulemaking (NFRM) dated January 2015, all control cables made of AISI 303 Se or AISI 304 stainless steel have to be replaced after 15 calendar years of service.

Owners of aircraft with effected cables will have until January 2018 to comply with the airworthiness directive.

Service Difficulty Reports (SDRs) submitted to CASA over the past seven years show a total of 48 control cable terminals being reported unserviceable.

"The majority of aircraft were reported to have more than one unserviceable control cable terminal installed," the NFRM states. "In order to help mitigate the unsafe condition caused by stress corrosion cracking in control cable terminals manufactured from SAE-AISI 303 Se or SAE-AISI 304 stainless steel, CASA will impose a mandatory retirement for primary flight control (PFC) cable assemblies that have been in service for 15 years or more."

The decision to retire stainless steel control cables follows on from an Australian Transport Safety Bureau investigation report released in April 2013, which concluded that cables made from certain stainless steels were susceptible to Stress Corrosion Cracking (SCC).

In the report, the ATSB stated that inspection was an "incomplete defence" against failures attributed to SCC and that the issue was related to the ageing general aviation fleet.

An incident in April 2005 when a Beech V35A Bonanza lost control response near Benalla was cited in the ATSB report as the reason CASA implemented a 2011 recommendation to retire the cables after 15 years, which has now been mandated under the NFRM.

More information on the mandate is available from the CASA website. The ATSB report is available on the ATSB website.

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