What happened
On October 18, 2012, an L 410 UVP-E9, registration OK-RDA, operated by VAN AIR Europe, was performing a scheduled flight from Ronaldsway Airport, Isle of Man, to Newcastle. Approximately ten minutes after takeoff, the crew observed a drop in oil pressure and a subsequent rise in inter-turbine temperatures on the right engine.
Following established operating procedures, the pilot elected to shut down the right engine and initiate an immediate return to the departure aerodrome. The crew notified Isle of Man air traffic control of the situation. The aircraft landed safely on runway 26 without further incident. There were no injuries to the two crew members or the eight passengers, and the aircraft sustained no damage during the landing.
The investigation
The ÚZPLN investigation focused on the technical failure of the right engine, a Walter M601E. The engine was removed and sent for expert analysis. The investigation examined the engine's maintenance history, noting that the aircraft had been maintained in accordance with all required procedures and had undergone a recent inspection in August 2012.
Technical examination of the engine revealed seizure and damage to the main bearing. Specifically, investigators found a break in the torsion shaft of the oil scavenging pump drive. Upon inspecting the inlet of the oil scavenging pump, investigators discovered a foreign object: a fragment of a retaining ring. Metalographic analysis of the ring material ruled out a material defect.
Findings
The investigation established that the incident was caused by a fragment of a retaining ring entering the inlet of the oil scavenging pump. This intrusion caused the torsion shaft of the pump drive to twist and break, which interrupted the oil flow within the engine's lubrication system. The resulting loss of oil pressure led to the seizure of the main bearing and the increase in inter-turbine temperatures.
Safety action
Following the findings, the following actions were recommended:
- The engine manufacturer and the gearbox supplier should implement effective measures to prevent the recurrence of retaining ring failure during the assembly of M601-5.6.SP922/89 gearbox components.
- The engine manufacturer should notify M601 engine users of the event through its information system.
- The engine manufacturer should update the inspection technology for oil strainers within the gearbox via a service bulletin.