Airworthiness Directives; Bombardier Model CL-600-2B16 (CL-604) Airplanes and Model CL-600-2B19 (Regional Jet Series 100 & 440) Airplanes

The FAA is superseding two existing airworthiness directives (ADs), that apply 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. One existing AD requires replacing the horizontal stabilizer trim control unit (HSTCU) with a new HSTCU. The other existing AD requires revising the airplane flight manual (AFM) to advise the flightcrew of procedures to follow in the event of stabilizer trim runaway, and in the event of MACH TRIM, STAB TRIM, and horizontal stabilizer trim malfunctions; and revising the AFM to require a review of the location of certain circuit breakers. That AD also requires doing a functional check of the stabilizer trim system and installing circuit breaker identification collars, and provides an optional terminating action. This new AD requires the previously optional terminating action and requires further revisions to the AFM. This AD also requires the removal of certain AFM revisions. This AD results from reports of trim problems including uncommanded trim, trim in the opposite direction to that selected, loss of trim position indication and, in one case, potential loss of trim disconnect capability. We are issuing this AD to prevent these events, which could result in conditions that vary from reduced controllability of the airplane to loss of control of the airplane.