Overview
A gearbox retainer ring failed during operation, with the fracture occurring within the required inspection intervals. The operator had implemented several preventive maintenance measures, including gearbox overhauls, spectrometric oil analysis (SOAP), magnetic drain plug inspections, and propeller dynamic balance checks. Despite these measures, none of the inspections detected any anomalies before the failure.
Maintenance History
The most recent overhaul of the gearbox took place approximately 2,429 flight hours prior to the failure. At that time, a new retainer ring was installed. The operator followed the manufacturer's recommended maintenance schedule for all gearbox-related inspections.
Inspection Findings
During the period between the overhaul and the failure, the operator performed regular SOAP analyses, magnetic drain plug inspections, and propeller dynamic balance checks. None of these inspections revealed any indications of an impending failure. The retainer ring failed without prior warning, and the inspections did not identify any abnormality that would have suggested the component was near the end of its service life.