What happened
On July 29, 2002, a Grob G 115, registration PH-SPC, was performing a triangular flight pattern between Seppe, Ameland, and Hoogeveen. During the final leg of the flight back to Seppe, the pilot noticed light vibrations while flying near Deventer. Although the pilot performed engine checks and found no immediate abnormalities, the vibrations persisted. After notifying air traffic control, the decision was made to divert to Teuge airport.
As the aircraft descended, the vibrations intensified and engine power began to decrease. Despite the pilot's efforts to manage the descent, the engine stopped completely during the final approach. The pilot managed to reach the runway, and the aircraft landed without further incident, though the engine sustained light damage.
The investigation
Investigators examined the Lycoming O235-H2C engine and discovered that the third cylinder had broken off just above its base. This failure caused the piston to seize and resulted in a severely deformed connecting rod. The intense vibrations from the failure also caused the engine mount rubber buffers to tear. Furthermore, the investigation revealed a significant loss of oil; only about half a liter of the required 4 liters remained in the engine block.
Microscopic and macroscopic analysis determined that the cylinder breakage was caused by external corrosion. This corrosion weakened the material, allowing cracks to form under operational stress, which eventually led to the complete separation of the cylinder. It is believed the structural failure occurred shortly before landing, at which point the oil began to leak out.
Findings
- The primary cause of the engine failure was the structural failure of the third cylinder due to external corrosion.
- The corrosion led to fatigue cracking and the eventual breakage of the cylinder base.
- The loss of oil was a consequence of the cylinder breaking, rather than the initial cause of the vibrations.
- While this was the first recorded instance of such cylinder corrosion in the Netherlands, the phenomenon had been documented in France for this specific engine type.