Airworthiness Directives; Saab Model SAAB-Fairchild SF340A (SAAB/SF340A) and SAAB 340B Airplanes

The FAA is superseding an existing airworthiness directive (AD), which applies to certain Saab Model SAAB-Fairchild SF340A and SAAB 340B airplanes. That AD currently requires repetitive inspections for wear of the brushes and leads and for loose rivets of the direct current (DC) starter generator, and related investigative/corrective actions if necessary. This new AD requires installing new, improved generator control units (GCUs). Installing the GCUs ends the repetitive inspection requirements of the existing AD. This AD results from reports of premature failures of the DC starter generator prior to scheduled overhaul. We are issuing this AD to prevent failure of the starter generator, which could cause a low voltage situation in flight and result in increased pilot workload and reduced redundancy of the electrical powered systems.