Summary
We propose to adopt a new airworthiness directive (AD) for certain Bombardier, Inc. Model DHC-8-400 series airplanes. This proposed AD was prompted by reports of chafing found on the main landing gear (MLG) yoke. The chafing was attributed to contact between the nacelle fire detection wires and the MLG yoke. This proposed AD would require inspections of the nacelle fire detection wires and the MLG yoke for damage; replacing nacelle fire detection wires, if necessary; repairing the MLG yoke, if necessary; and installing new brackets and associated hardware to secure the fire detection wires. We are proposing this AD to prevent chafing between the nacelle fire detection wires and the MLG yoke. Chafing could lead to cracking and subsequent failure of the MLG yoke, which could adversely affect the safe landing of the airplane. In addition, chafing of the nacelle fire detection wires could cause them to fail and prevent the detection of a fire in the nacelle assembly.