AD FAA-2016-4224

We are adopting a new airworthiness directive (AD) for certain Bombardier, Inc. Model DHC-8-400 series airplanes. This AD was prompted by reports of cracked and corroded barrel nuts found at the mid-spar location of the horizontal-stabilizer-to-vertical-stabilizer attachment joint. This AD requires repetitive detailed inspections of each barrel nut and cradle, a check of the bolt torque of the preload indicating (PLI) washers, and corrective action if necessary. We are issuing this AD to address the unsafe condition on these products.