Summary
We propose to adopt a new airworthiness directive (AD) for certain Bombardier, Inc. Model DHC-8-400 airplanes. This proposed AD was prompted by one in-service report of a cracked and corroded barrel nut found at the mid-spar location of the horizontal stabilizer to vertical stabilizer attachment joint. There have also been two other reports of corroded barrel nuts found at mid-spar locations. This proposed AD would require repetitive detailed inspections of each barrel nut and cradle, a check of the bolt torque of any preload indicating washer (PLI), and corrective action if necessary. We are proposing this AD to detect and correct cracked and corroded barrel nuts. This condition could compromise the structural integrity of the vertical stabilizer attachment joints, which could lead to loss of control of the airplane.