Airworthiness Directives; Eurocopter France Model AS-350B, BA, B1, B2, C, D, and D1, and AS-355E, F, F1, F2 and N Helicopters

This amendment revises an existing airworthiness directive (AD), applicable to Eurocopter France Model AS-350B, BA, B1, B2, C, D, and D1, and AS-355E, F, F1, F2 and N helicopters, that currently requires repetitive inspections of the main rotor head components, the main gearbox (MGB) suspension bars, and the ground resonance prevention system components at intervals not to exceed 400 hours time-in-service (TIS). This amendment requires the same inspections, but at intervals not to exceed 500 hours TIS. This amendment is prompted by reports of confusion and unnecessary costs associated with the difference in the current 400 hours TIS inspection interval and the current manufacturer's master service recommendation of 500 hours TIS inspection interval. The actions specified by this AD are intended to eliminate confusion and unnecessary costs and to prevent ground resonance due to reduced structural stiffness, which could lead to failure of a main rotor head or MGB suspension component and subsequent loss of control of the helicopter.