Summary
This document proposes to supersede Airworthiness Directive (AD) 90-12-08, which currently requires the following on de Havilland Model DHC-3 airplanes: repetitively inspecting (using dye penetrant methods) the tailplane main rib forward flanges and the main rib forward lower flanges at the tailplane front attachment fitting for cracks and repairing any cracked flange. The proposed action would retain the repetitive inspections currently required by AD 90-12-08, and would allow the provision of incorporating a certain modification as terminating action for these repetitive inspections. The proposed action is prompted by the Federal Aviation Administration's determination that installing new angles and plates on the tailplane root ribs on de Havilland Model DHC-3 airplanes provides an equivalent level of safety to the repetitive inspections required by AD 90-12-08. The actions specified by the proposed AD are intended to prevent failure of the tailplane structure caused by cracked tailplane main rib forward flanges or main rib forward lower flanges at the tailplane front attachment fitting, which, if not detected and corrected, could result in loss of control of the airplane.