Airworthiness Directives; de Havilland DHC-6 Series Airplanes

This amendment supersedes Airworthiness Directive (AD) 78-26- 02, which currently requires repetitively inspecting the fuselage side frame flanges at Fuselage Station (FS) 218.125 and FS 219.525 for cracks on certain de Havilland DHC-6 series airplanes, and repairing or replacing any cracked part. The Federal Aviation Administration's policy on aging commuter-class aircraft is to eliminate or, in certain instances, reduce the number of certain repetitive short-interval inspections when improved parts or modifications are available. This AD requires modifying the fuselage side frames at the referenced FS areas as terminating action for the repetitive inspections that are currently required by AD 78-26-02. The actions specified in this AD are intended to prevent failure of the fuselage because of cracks in the fuselage side frames, which, if not detected and corrected, could result in loss of control of the airplane.