FAA 2019-03-29

Requires modifying the left-hand hydraulic system of the nose wheel steering (NWS) control system and, for certain airplanes, torquing the fittings on a certain tube assembly. AD was prompted by an incident of uncommanded NWS in-service; subsequent investigation revealed that the steering selector valve is susceptible to jamming in the open position due to particulate contamination of the hydraulic system.