What happened
On November 24, 2020, a Lighter 600 aircraft, registration SP-SUNY, was performing a flight from Robakowo near Grudziądz to Rudniki (EPRU). While cruising at an altitude of 600 m AGL, the aircraft experienced a sudden loss of engine power accompanied by intense vibrations. The pilot had not made any changes to the engine parameters prior to the event.
In an attempt to stabilize the aircraft, the pilot reduced engine power to the minimum setting, but the vibrations persisted. Consequently, the pilot decided to shut down the engine and performed an emergency landing in an unprepared field. During the final phase of the landing roll, the soft ground caused damage to the nose landing gear strut and the propeller spinner. The pilot sustained no injuries.
The investigation
Following the incident, the ROTAX 912 ULS2 engine was inspected at its home base. Upon removing the valve cover of cylinder number 2, investigators found a malfunctioning intake valve, significant debris from the intake valve guide, and damage to the valve retaining locks and seals. \nTo determine the root cause, the engine was sent to an authorized Rotax service provider for a complete teardown. The detailed disassembly revealed that the intake valve stem and head of cylinder number 2 had fractured, and the valve spring retainer had also broken. Furthermore, metal shavings from the failure in cylinder number 2 had migrated to the other cylinders and carburetors. Because the broken valve components had struck the moving piston, the specific nature of the fracture could not be analyzed to determine the original cause of the stem failure. The engine had only 54 hours of total time in service.