What happened
On 1 June 2019, a Sky Arrow 650T, registration G-BYCY, was performing a private cross-country flight along the Welsh coast. As the pilot was on the downwind leg approaching Newport City Aerodrome, they experienced a noticeable rumble originating from the rear of the aircraft, followed by a complete engine stoppage.
Realising the airfield could not be reached, the pilot turned the aircraft into the wind and executed a forced landing in a nearby field. Although the field appeared suitable from the air, it contained numerous ditches that were not visible during the approach. The impact with the uneven terrain resulted in the aircraft being beyond economic repair, though the pilot escaped with only minor injuries.
The investigation
Following the accident, the AAIB conducted an examination of the Rotax 914-UL piston engine. Working alongside the Light Aircraft Association (LAA), investigators identified a catastrophic mechanical failure involving one of the connecting rods, which had broken and protruded from the crankcase.
Technical analysis focused on the No 3 connecting rod big end bearing and journal, which also caused significant secondary damage to the No 3 piston. Examination of the bearing fragments indicated that the failure was likely driven by lubricating oil starvation, which caused accelerated wear. While the other bearings and journals appeared to be in normal, well-lubricated condition, investigators could not confirm if an initial bearing defect caused the lubrication failure or if a lubrication issue directly caused the bearing to fail.