Airworthiness Directives; Bombardier, Inc. Airplanes

We are adopting a new airworthiness directive (AD) for all Bombardier, Inc. Model DHC-8-400 series airplanes. This AD was prompted by a revision by the manufacturer to the Certification Maintenance Requirements (CMR) of the Airworthiness Limitation Items (ALI), in the Maintenance Requirement Manual (MRM), that introduces a new CMR task that requires repetitive operational checks of the propeller overspeed governor. This AD requires revising the airplane maintenance or inspection program, as applicable, to incorporate a new CMR task. We are issuing this AD to prevent dormant failure of the propeller overspeed governor, which may lead to a loss of propeller overspeed protection and result in high propeller drag in flight.