What happened
On March 21, 2006, at approximately 11:07 UTC, a DV 20 Katana, registration HOAC-Austria, was conducting a non-commercial flight from Beilngries, Germany, to Wr. Neustadt/Ost, Austria. The flight was intended to deliver the aircraft for a scheduled 6,000-hour inspection.
While cruising at approximately 4,000 feet MSL, the pilot noticed a sudden drop in oil pressure. Shortly thereafter, the Rotax 912 S3 engine failed completely. The pilot was forced to perform an emergency landing in the municipality of Groß-Schollach, near the A1 motorway. The aircraft successfully touched down in a plowed field and came to a halt after a short ground roll. The pilot escaped the incident without injury, and while the engine showed signs of oil loss and could not be rotated by hand, there was no visible external damage to the airframe.
The investigation
The Austrian SUB investigation focused on the technical failure of the engine and the maintenance history of the aircraft. Investigators performed a detailed technical examination of the Rotax 912 S3 engine, including the inspection of the crankcase, pistons, and valve train. The investigation also reviewed the aircraft's maintenance records, specifically regarding the engine's oil system and the adherence to operating and maintenance instructions.
Findings
- The primary cause of the engine failure was a complete fracture of the valve spring retainer on the exhaust valve of cylinder 3.
- Evidence suggested that the failure was likely exacerbated by oil starvation or the presence of air within the valve train of cylinder 3.
- A maintenance deficiency was identified in the engine's airframe-side oil system, specifically related to the failure to strictly follow established operating and maintenance instructions.