Right Engine Gearbox Failure Prompts In-Flight Shutdown and Landing (N223AS)

Incident Overview

This incident occurred as the flight crew was initiating a descent into final approach for a landing. The right engine gearbox chip detector illuminated, which was followed by a loud bang and severe vibration. In response, the crew feathered the propeller and shut down the engine using the condition lever. When the propeller was feathered and the engine shut down, the rotation and vibration stopped. The crew subsequently landed the aircraft without any further incident.

Powerplant Investigation

A teardown inspection of the powerplant was performed at the factory. The examination revealed a sudden and catastrophic failure of the propeller reduction gearbox assembly. The cause of this failure was a high cycle metal fatigue fracture on one of two helical gears within the gearbox.

Propeller Assembly Investigation

The propeller assembly was also subjected to a teardown and inspection. The inspection revealed severe damage to the composite plastic blade retainer rings and the metal actuator yokes. This damage was caused by the sudden deceleration and stoppage of the propeller after the gearbox failure.