Summary
We propose to adopt a new airworthiness directive (AD) for the products listed above. This proposed AD results from mandatory continuing airworthiness information (MCAI) originated by an aviation authority of another country to identify and correct an unsafe condition on an aviation product. The MCAI describes the unsafe condition as:
Cracked nuts * * * were found on aircraft's production line during routine post assembly inspection. Investigation revealed that the cracks resulted from hydrogen embrittlement combined with high hardness. Non-conformity with certified mechanical properties of this fastener can potentially lead to an unsafe condition.
The unsafe condition is cracked nuts in multiple locations (including aileron fittings, rudder tab assembly and mounting structure for power drive units) could result in failure of affected locations and consequent reduced controllability or reduced structural capability of the airplane. The proposed AD would require actions that are intended to address the unsafe condition described in the MCAI.