What happened
On February 13, 2009, a pilot was conducting a local flight from the Besançon Thise airfield in France. Shortly after takeoff from an unpaved runway, while the A Aeroskyranger was climbing to approximately 600 feet and executing a left turn, the propeller detached from the aircraft. Following the separation, the pilot performed a turnaround and executed an emergency landing on the opposite runway (runway 06).
The investigation
The investigation focused on the mechanical failure of the propeller assembly. The aircraft was powered by a Rotax 582 engine equipped with a type "B" reduction gear. Investigators found that the propeller shaft had become disconnected from the reduction gear. The connection between the shaft and the gear was maintained by semi-circular keys (crescents) housed within a cage. Upon inspection, the cage was found broken into two pieces, and both semi-circular keys were damaged.
Evidence revealed that the aircraft had been involved in a hard landing in June 2008, which resulted in a nose-over. While the airframe was repaired and the propeller was replaced, the reduction gear was only subjected to a visual inspection. The engine was maintained by a workshop that did not specialize in aviation, and the reduction gear was not included in their maintenance scope. Instead, the owners performed visual inspections themselves. The propeller separation occurred approximately 45 flight hours after the propeller had sustained a prior impact.
Findings
- The mechanical failure was caused by the underestimation of the consequences of a propeller strike.
- The reduction gear assembly had not been maintained in accordance with the engine maintenance manual, which requires a specialized press to check and adjust spring pressure every 100 flight hours.
- Following a previous propeller impact, the reduction gear was only visually inspected rather than being professionally assessed.
- Rotax technical bulletins specify that only authorized personnel should evaluate damage from propeller strikes and that the engine must be inspected or overhauled following such an event.