What happened
On 7 April 2007, a X’Air V2(2) microlight, registration G-CBBH, departed from Chatteris for a routine touch-and-go maneuver at Sutton Meadows. The flight was a private operation involving one pilot and one passenger. Shortly after the aircraft climbed to an altitude of approximately 150 ft, the engine experienced a significant loss of power.
While attempting to complete the maneuver, the pilot identified a large ditch ahead that posed a collision risk. To avoid the obstacle, the pilot maneuvered the aircraft to the left. This course correction resulted in the left main landing gear making contact with the ground first, causing the gear to collapse. The aircraft subsequently slid into a field containing recently planted crops, where the nose wheel dug into the soft soil. The impact caused the aircraft to pitch forward onto its nose, resulting in damage to the forward fuselage pod, the windscreen, and the left main and nose landing gears, as well as a broken propeller blade. There were no injuries to the occupants.
The investigation
The investigation focused on the sudden loss of engine power and the subsequent mechanical state of the powerplant. During the post-accident inspection, the engine was found to be difficult to rotate by hand, suggesting a partial seizure. A detailed teardown of the Simonini Racing Victor II engine revealed that the rear cylinder big-end bearing had failed, leaving metallic fragments scattered throughout the crankcase.
Investigators also analyzed the fuel/oil mixture. Samples taken from the fuel line and the fuel tank showed oil concentrations of 3.2% and 2.3% by volume, respectively. While the concentrations varied slightly, both levels were within the range required for the engine's operation, as the owners used motor gasoline with added oil.
Findings
- The primary cause of the power loss was the failure of the rear cylinder big-end bearing.
- The engine, a two-stroke water-cooled model, relies on the fuel/oil mixture for lubrication.
- Although there was a slight discrepancy in oil concentration between the fuel line and the tank, the levels were considered sufficient to maintain lubrication and were not the cause of the failure.