What happened
On July 19, 2017, a Cessna P210N, registration OK-TGM, was performing a VFR flight from Warsaw/Babice to Lodz/Lublinek when the pilot experienced a sudden engine malfunction. Approximately 25 minutes into the flight, the pilot noted a sudden increase in propeller RPM and received a "Warning" signal on the engine monitor. Subsequent checks revealed zero oil pressure and a significant drop in manifold pressure.
Following the loss of oil pressure, the pilot declared a MAYDAY and initially attempted to divert to Lodz/Lublinek. However, as engine performance continued to deteriorate, the pilot decided to execute an emergency landing in a field near Justyn and Adamów. To prevent propeller damage, the pilot extended the landing gear, shut down the engine, and moved the fuel selector to the "OFF" position just before touchdown. The aircraft landed in a high corn crop within a tractor furrow. The pilot was uninjured, and the aircraft sustained no significant damage.
The investigation
The ÚZPLN investigation focused on the engine's power unit to determine the cause of the sudden oil pressure loss. An inspection of the Continental TSIO 520 P5B engine revealed that the oil pump drive shaft had fractured at the gear interface. Metal fragments were found on the magnetic plug and within the oil pan.
Investigators examined the history of the oil pump repair. It was discovered that the drive shaft had previously undergone a repair using laser cladding (laser cladding with 210ST material) followed by grinding. While magnetic testing after this repair had shown no defects, the engine manufacturer's maintenance manual does not include instructions for using laser cladding for this specific component. Furthermore, the investigation noted that the oil pump housing itself had been repaired via welding, which may have potentially affected the alignment of the bearings.
Findings
- The primary cause of the incident was the interruption of the oil supply to the engine due to the sudden failure of the oil pump drive shaft.
- The failure of the shaft was attributed to fatigue and vibrational wear on the surface of the shaft, specifically in the area where the laser cladding repair had been applied.
- The use of laser cladding for the shaft repair was not an approved method according to the engine manufacturer's maintenance instructions.
- Potential misalignment of the bearings, resulting from the previous repair of the pump housing, may have contributed to the stress concentration leading to the fracture.
- The pilot's timely decision to perform an emergency landing in a suitable field prevented further damage to the aircraft.