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:
A specific failure case of the THSA [trimmable horizontal stabilizer actuator] upper primary attachment, which may result in a loading of the upper secondary attachment, has been identified by analysis.
Primary load path failure can be caused by bearing migration from the upper attachment gimbal by failure or loss of a retention bolt.
In case of failure of the THSA upper primary attachment, the THSA upper secondary attachment would engage. Because the upper attachment secondary load path can only withstand the loads for a limited period of time, the condition where it would be engaged could lead, if not detected, to the failure ofthe secondary load path, which would likely result in loss of control of the aeroplane.
The proposed AD would require actions that are intended to address the unsafe condition described in the MCAI.