AD 2009-15-15 Amendment 39-15978

We are adopting a new airworthiness directive (AD) for Bell Helicopter Textron Canada (BHTC) Model 427 helicopters. This AD results from mandatory continuing airworthiness information (MCAI) originated by the aviation authority of Canada to identify and correct an unsafe condition on an aviation product. Transport Canada, the aviation authority of Canada, with which we have a bilateral agreement, states that it has been determined that the existing hardware connecting the vertical fin to the tail rotor gearbox needs to be upgraded to prevent the vertical fin from becoming loose. BHTC has received reports of loose vertical fins discovered during inspections. Investigation revealed that the current vertical fin attachment hardware may not provide adequate clamp-up. If not corrected, the vertical fin could become loose and cause vibration, which could lead to subsequent loss of control of the helicopter. This AD requires actions that are intended to address this unsafe condition.