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

The FAA is superseding an existing airworthiness directive (AD), which applies to certain Bombardier Model DHC-8-400 series airplanes. That AD currently 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, the existing AD requires doing repetitive visual inspections for cracking of the barrel nuts and cradles and replacing all hardware for all cracked barrel nuts. The existing AD also requires replacing all hardware for certain affected barrel nuts that do not have cracking, which would end the repetitive inspections for those airplanes. The existing AD also provides an optional replacement for all affected barrel nuts. This new AD requires replacing all affected barrel nuts and applying a certain compound to the affected barrel nuts and bolts. 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.