Summary
We propose to revise an existing airworthiness directive (AD) for the products listed above. This proposed AD results from mandatory continuing airworthiness information (MCAI) issued 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:
During production of Arriel 1 and Arriel 2 Power Turbine (PT) wheels, geometric non-conformances on blade fir tree roots have been detected by Turbom ca. Potentially non-conforming PT blades have been traced as having been installed on Module M04 (PT) listed in Mandatory Service Bulletin (MSB) A292 72 0827 for Arriel 1 engines and A292 72 2833 for Arriel 2 engines.
The geometric non-conformities of the blades may potentially lead to a reduction in the fatigue resistance of PT blades to a lower level than their authorized in service use limit. This reduction of fatigue resistance can potentially result in blade release, which could cause an uncommanded in-flight shutdown.
We are proposing this AD to prevent release of PT blades, which could result in an uncommanded in-flight shutdown and emergency autorotation landing.