Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to certain Bombardier Model DHC-8-401 and -402 airplanes. This proposal would require modifying the wiring of the rudder trim switch, inspecting all wiring on the back of the aileron/rudder trim control panel for chafing, and replacing any chafed wiring with new wiring. This action is necessary to prevent a short circuit on the aileron/rudder trim control panel that could cause a runaway condition of the rudder trim actuator, which could result in reduced controllability of the airplane. This action is intended to address the identified unsafe condition.