Airworthiness Directives; Bombardier, Inc. Airplanes

We are adopting a new airworthiness directive (AD) for certain Bombardier, Inc. Model CL-600-2A12 (CL-601 Variant), and CL-600-2B16 (CL-601-3A, CL-601-3R, and CL-604 Variants) airplanes. This AD was prompted by a report that a potential chafing condition exists between the negative-G fuel feed drain line of the auxiliary power unit (APU) and its surrounding structure and components. This AD requires, for certain airplanes, a detailed inspection for chafing conditions of the negative-G fuel feed drain line of the APU, and corrective actions if necessary. For certain other airplanes, this AD requires replacement of the APU negative-G fuel feed tube assembly and the drain line. We are issuing this AD to address the unsafe condition on these products.