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Final rule.
We are adopting a new airworthiness directive (AD) for Airbus Helicopters Model AS355E, AS355F, AS355F1, AS355F2, and AS355N helicopters. This AD requires measuring a vibration level in the tail rotor (T/R) drive. This AD was prompted by reports of bearing degradation. The actions of this AD are intended to prevent an unsafe condition on these helicopters.