Summary
We are revising an earlier proposed airworthiness directive (AD) for certain Saab AB, Saab Aerosystems Model SAAB 340A (SAAB/ SF340A) and SAAB 340B airplanes. The first supplemental NPRM would have required inspecting the fuselage surface for corrosion and cracking behind the external adapter plate of the antennae installation, and repair if necessary. The first supplemental NPRM resulted from a report of a crack found behind the external adapter plate of the antennae during inspection. Similar cracking was found on two additional airplanes, and extensive corrosion was found on one airplane. This action revises the first supplemental NPRM by correcting an STC number, which would expand the applicability of the first supplemental NPRM. We are proposing this second supplemental NPRM to detect and correct corrosion and cracking behind the external adapter plate of the antennae of certain damage- tolerant structure, which could result in reduced structural integrity and consequentrapid depressurization of the airplane.