Airworthiness Directives; Bombardier Model CL-600-1A11 (CL-600), CL-600-2A12 (CL-601), and CL-600-2B16 (CL-601-3A, CL-601-3R, and CL-604) Series Airplanes

This amendment revises an existing airworthiness directive (AD), applicable to certain Bombardier Model CL-600-1A11 (CL-600), CL- 600-2A12 (CL-601), and CL-600-2B16 (CL-601-3A, CL-601-3R, and CL-604) series airplanes, that currently requires repetitive inspections to find cracks of a certain bulkhead web of the fuselage at certain locations, and repair if necessary. The actions specified by that AD are intended to prevent cracking in the pressure bulkhead at frame station (FS) 409.00, which could result in uncontrolled depressurization of the airplane and/or reduced structural integrity of the fuselage. This amendment provides an optional terminating modification for certain airplanes. This action is intended to address the identified unsafe condition.