Airworthiness Directives; Bombardier Model CL-600-2B19 (Regional Jet Series 100 & 440) Airplanes

We are adopting a new airworthiness directive (AD) for certain Bombardier Model CL-600-2B19 (Regional Jet Series 100 & 440) airplanes. This AD requires repetitive detailed inspections for cracking of the left side and right side frame and reinforcement angles at fuselage station (FS) 640 between stringer 9 and stringer 12, and corrective actions if necessary. This AD also provides an optional terminating action for the repetitive inspections. This AD results from reports that cracks have been discovered on the frame and reinforcement angles at FS 640. We are issuing this AD to detect and correct cracking of the frame, which could lead to failure of the fuselage structure and possible loss of the airplane.