What happened
Shortly after departing, an aircraft was observed at a low altitude with smoke trailing from its left engine. During the initial climb, witnesses noted the wings oscillating before the left wing descended and impacted the ground. The accident resulted in 12 fatalities, involving 11 parachutists located in the center of the fuselage and the crew. There was no evidence that the passengers were using restraints at the time of the impact.
Findings
An investigation into the mechanical failure determined that a supercharger bearing had failed within the left engine. This engine had been recently installed by personnel lacking proper certification following an 18-year period of inactivity without necessary preservation measures. Additionally, while the aircraft had flown approximately 184 hours since its last annual inspection, there was no documentation of a required 100-hour inspection being completed.
Technical analysis of the propeller revealed that the left blades were stuck in an intermediate position, neither fully operating nor feathered. Although the left propeller had been replaced a few weeks before the crash, there was no proof it had been successfully tested in the full feather position. The crew was reportedly unaware of service bulletins recommending that the propeller be checked for full feathering capability every 30 days. Furthermore, the relays for the left propeller feathering motor could not be recovered for examination.