What happened
On April 30, 2011, a Mooney M20J, registration LN-ABP, was performing a private VFR flight from Rakkestad Airport to Kristiansand. During the en route phase, approximately 2.5 NM west-northwest of Kjeller, the pilot noticed a complete loss of oil pressure.
In response to the emergency, the pilot executed a 180-degree turn to seek suitable landing sites and notified Oslo Approach. While the engine initially continued to run, the pilot eventually determined that the original intended landing site was unsuitable. As the aircraft proceeded toward Kjeller, the engine ceased operation entirely. The pilot performed an emergency landing in an upward slope at Bøler gård. The aircraft slid 118 meters on its belly before striking a fence. The pilot escaped the crash without injury.
The investigation
The Norwegian Safety Investigation Authority (NSIA) examined the aircraft, the engine, and the crash site. Physical evidence at the scene showed clear oil trails underneath the fuselage, consisting of light, clear oil. Upon disassembly of the engine, investigators found that the oil remaining in the sump was black, opaque, and smelled of burning.
Technical inspections of the engine revealed that the connecting rod for cylinder number 3 had broken, with the lower end having struck the oil sump. The rod bearing showed signs of overheating, and the rod bearing for cylinder number 2 was also worn and overheated. Metallurgical analysis of the broken connecting rod bolt by the Norwegian Defence Research Establishment concluded that the failure was likely caused by an overload occurring over a short period.
Findings
- The engine failed because it ran out of oil.
- The loss of oil likely occurred through the crankcase breather line, as no other significant leaks were identified in the oil lines, filters, or gaskets.
- The remaining oil in the sump had undergone significant overheating, evidenced by its dark color and burnt odor.
- The engine was sufficiently lubricated at the time of departure from Rakkessat, as the oil found under the fuselage was clear and light, suggesting the leak developed during the flight.
- The pilot managed the emergency effectively by maneuvering toward lower terrain and maintaining a lookout for obstacles.