Aircraft and Flight Information
The aircraft, a YAK-50 registered G-YAKK, with a single Ivchenko Vedeneyev M-14P piston engine, was being operated on a private flight from Carlisle Airport. The pilot, the sole occupant, held a Private Pilot's Licence and had 412 flying hours, including 56 on type.
Accident Events
On 10 April 2010 at 1142 UTC, while on a local flight near Bothel, Cumbria, the engine failed due to a loss of oil pressure. The windscreen became partially covered with an oil film, but the pilot was able to execute a forced landing in a field. During the landing, the aircraft sustained substantial damage. The pilot vacated the aircraft unaided but later attended hospital as injuries became apparent.
Post-Accident Examination
Upon examining the engine, the pilot discovered that the oil pressure adjustment valve was missing from the oil scavenge pump housing. The valve was later found in the lower cowling. The pilot believed that the valve had worked loose and fallen out during the flight, causing the oil loss. The aircraft had recently undergone extensive maintenance, including an overhaul of the oil scavenge pump assembly. Initial flights following this work revealed a small oil leak in the area of the pump, which at the time was thought to have been remedied by an engineer tightening the small vertical bolts adjacent to the pressure adjustment valve.