Airworthiness Directives; Bombardier, Inc., Airplanes

We are adopting a new airworthiness directive (AD) for certain Bombardier, Inc., Model BD-100-1A10 airplanes. This AD was prompted by an incident of uncommanded nose wheel steering (NWS) in-service; subsequent investigation revealed that the steering selector valve (SSV) is susceptible to jamming in the open position due to particulate contamination of the hydraulic system. This AD requires modifying the left-hand hydraulic system of the NWS control system and, for certain airplanes, torqueing the fittings on a certain tube assembly. We are issuing this AD to address the unsafe condition on these products.