Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to certain Saab Model SAAB SF340A and SAAB 340B series airplanes. This proposal would require visual and dye penetrant inspection(s) to detect cracks of the nose rib of the rudder, and stop drilling and blending of minor cracks. The proposal would also require replacement of the nose rib with a new nose rib and reinforcement of the nose rib, if estensive cracking is detected or if an operator elects to terminate the repetitive inspections. This proposal is prompted by the result of an inspection that revealed a cracked nose rib on the front spar of the rudder due to vibration- related stress. The actions specified by the proposed AD are intended to prevent such stress and cracking, which could result in the deformation of the nose rib; this condition may lead to friction and jamming between the fin and the rudder and subsequent reduced controllability of the airplane.