Action
Final rule.
Summary
We are adopting a new airworthiness directive (AD) for certain Bombardier, Inc. Model DHC-8-400, -401, and -402 airplanes. This AD was prompted by reports of movement of the rudder pedals being impeded due to corrosion of the trunnion shaft of the rudder feel trim unit (RFTU). This AD requires an inspection to determine if certain RFTUs are installed, an operational check for signs of seizure of affected parts, repetitive lubrication of certain RFTUs, and replacement of the RFTU if necessary. Installing replacement RFTUs having conformal bushings terminates the repetitive lubrication requirements. We are issuing this AD to detect and correct any sign of rough movement or seizure of the trunnion shaft and its bushing, which could cause a rudder control jam or a large and rapid alternating rudder input leading to a structural failure of the vertical fin.