Summary
We propose to adopt a new airworthiness directive (AD) for certain Bombardier, Inc. Model DHC-8-400 series airplanes. This proposed AD was prompted by a determination by the manufacturer that shims might not have been installed between certain longerons and longeron joint fittings. This proposed AD would require repetitive inspections of the external surface of the fuselage skin panel for loose or working fasteners, and corrective action if necessary; a detailed visual inspection of the longeron joint fittings for the existence of shims and, if necessary, repetitive inspections of the longeron and the longeron joint fittings for any cracking, and corrective action if necessary. This proposed AD would also provide terminating action for certain repetitive inspections. We are proposing this AD to detect and correct missing shims between the longerons and longeron joint fittings. Such missing shims could result in a gapping condition and lead to stress corrosion cracking of the longeron joint fittings, and could adversely affect the structural integrity of the wing-to-fuselage attachment joints.