Airworthiness Directives; Bombardier Model DHC-8-400 Series Airplanes

The FAA is adopting a new airworthiness directive (AD) for certain Bombardier Model DHC-8-400 series airplanes. This AD requires inspecting all barrel nuts to determine if the barrel nuts have a certain marking, inspecting affected bolts to determine if the bolts are pre-loaded correctly, and replacing all hardware if the pre-load is incorrect. For airplanes on which the pre-load is correct, this AD requires doing repetitive visual inspections for cracking of the barrel nuts and cradles and replacing all hardware for all cracked barrel nuts. This AD also requires replacement of all hardware for certain affected barrel nuts that do not have cracking, which would end the repetitive inspections for those airplanes. This AD also provides an optional replacement for all affected barrel nuts. This AD results from reports of cracking in the barrel nuts at the four primary front spar wing-to-fuselage attachment joints. We are issuing this AD to detect and correct cracking of the barrel nuts at the wing front spar wing-to- fuselage joints, which could result in reduced structural integrity of the wing-to-fuselage attachments and consequent detachment of the wing.