Summary
The FAA is revising an earlier NPRM for an airworthiness directive (AD) that applies to certain Bombardier Model CL-600-2B16 (CL-604) airplanes and Model CL-600-2B19 (Regional Jet Series 100 & 440) airplanes. These models may be referred to by their marketing designations as RJ100, RJ200, RJ440, CRJ100, CRJ200, CRJ440, and CL-65. The original NPRM would have superseded an existing AD that currently requires revising the Emergency Procedures section of the airplane flight manual (AFM) to advise the flightcrew of additional procedures to follow in the event of stabilizer trim runaway. The existing AD also requires revising the Abnormal Procedures section of the AFM to advise the flightcrew of procedures to follow in the event of MACH TRIM, STAB TRIM, and horizontal stabilizer trim malfunctions. The existing AD also requires revising the Normal section of the AFM to require a review of the location of certain circuit breakers and a functional check of the stabilizer trim system. In addition, the existing AD requires installing circuit breaker identification collars and provides an optional terminating action for the requirements of the AD. The original NPRM proposed to require doing the previously optional terminating action (installation of a new horizontal stabilizer trim control unit). The original NPRM resulted from a determination that the terminating action is necessary to address reports of uncommanded horizontal stabilizer trim motion. This new action revises the original NPRM by not allowing the removal of applicable temporary revisions (TRs) to the Emergency and Abnormal Procedures sections of the AFM and by adding the proposed requirement for certain airplanes to re-insert the applicable TRs of the Emergency and Abnormal Procedures sections of the AFM under certain conditions. We are proposing this supplemental NPRM to prevent horizontal stabilizer trim uncommanded motion, which could result in reduced controllability of the airplane.