Summary
This document proposes to revise an earlier proposed airworthiness directive (AD), which would have superseded AD 78-26-02. That AD 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 previous document would have required 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. As currently written, the document allows continued flight if cracks are found in the fuselage side frames that do not exceed certain limits. Since publication of that proposal, the Federal Aviation Administration (FAA) has established a policy to disallow airplane operation when known cracks exist in primary structure (the fuselage area is considered primary structure). The actions specified by the proposed 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. Since the comment period for the original proposal has closed and the change described above goes beyond the scope of what was originally proposed, the FAA is allowing additional time for the public to comment.