Airworthiness Directives; Bombardier, Inc. Airplanes

We are adopting a new airworthiness directive (AD) for certain Bombardier, Inc. Model DHC-8-102, -103, -106, -201, -202, -301, -311, and -315 airplanes. This AD was prompted by reports of un-annunciated failures of the direct current (DC) starter generator, which caused caution indicators of the affected systems to illuminate and prompted emergency descents and landings. This AD requires replacing the DC generator control units (GCUs) with new GCUs and replacing the GCU label. We are issuing this AD to prevent a low voltage condition on the left main DC bus, which, during critical phases of flight, could result in the loss of flight management, navigation, and transponder systems, and could affect continued safe flight.