Airworthiness Directives; MD Helicopters, Inc. Model 600N Helicopters

This document supersedes an existing airworthiness directive (AD) for MD Helicopters, Inc. (MDHI) Model 600N helicopters. That AD currently requires interim initial and repetitive inspections of tailboom parts, installing six inspection holes in the aft fuselage skin panels, installing tailboom attachment bolt washers, modifying both access covers, and replacing broken attachment bolts. The current AD also provides for modifying the fuselage aft section as an optional terminating action. This amendment requires modifying the fuselage aft section within the next 24 months to strengthen the tailboom attachment fittings and upper longerons. The actions specified by this AD are intended to prevent failure of the tailboom attachment fittings, separation of the tailboom from the helicopter, and subsequent loss of control of the helicopter.