What happened
During the takeoff phase, the pilot of the PT6A-34 powered aircraft retracted the landing gear in accordance with established procedures. Immediately following this action, an explosion occurred, resulting in a total loss of power to the left engine. The pilot observed that the engine gauges dropped to zero and the propeller had stopped. In an attempt to manage the emergency, the pilot applied full power to the remaining engine while maintaining a flaps setting of 25 percent.
Despite applying significant right rudder, the pilot was unable to counteract a left-turning descent. The aircraft failed to maintain necessary airspeeds, and the stall warning horn remained active throughout the descent. The aircraft eventually impacted the ground, resulting in the destruction of the airframe.
Findings
Investigation into the engine failure revealed a fatigue fracture in the first-stage sun gear. While the engine's planet gear assembly had been replaced during a previous overhaul, the mating sun gear had been reinstalled, which was a common practice at the time. However, the manufacturer later specified that both components should be replaced simultaneously to avoid mismatched wear patterns. The sun gear in this instance had exceeded the manufacturer's recommended reliable operating timeframe, having reached over 22,000 hours.
Several maintenance and oversight deficiencies contributed to the accident:
- The operator's engine maintenance program was less restrictive than updated manufacturer reliability standards.
- There were significant gaps in the operator's engine trend monitoring, including missing and inaccurate data.
- Delays in oil analysis testing meant that a sample showing increased iron levels—indicating declining engine health—was not processed until after the crash.
- The aircraft's trim was not properly adjusted to compensate for the asymmetric thrust, and the pilot failed to maintain the necessary airspeed for a single-engine climb.
- Regulatory oversight failed to detect inadequacies in the operator's maintenance practices and part-tracking protocols.