Summary
The FAA is revising an earlier NPRM for an airworthiness directive (AD) that applies to certain Bombardier Model DHC-8-400 series airplanes. The original NPRM would have superseded an existing AD that currently requires inspecting all barrel nuts to determine if the barrel nuts have a certain marking, inspecting affected bolts to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 replacement of 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. The original NPRM proposed to require replacement of all affected barrel nuts. The original NPRM resulted from reports of cracking in the barrel nuts at the four primary front spar wing-to-fuselage attachment joints. This new action revises the original NPRM by adding, for certain airplanes, application of a certain compound to the affected barrel nuts and bolts. We are proposing this supplemental NPRM 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.