Accident Overview
On 15 September 2018, a Flight Design CTSW microlight aircraft, registration G-KEVK, suffered an engine failure approximately 5 nm north of Sywell Aerodrome during a local private flight. The two occupants, both qualified pilots on the type, were uninjured. The aircraft sustained substantial damage and was beyond repair.
Flight History
The flight departed Sywell for a local sortie. After flying to Denethorpe Airfield and completing four circuits, the pilots proceeded west for sightseeing over Market Harborough. While turning left to position for the return approach to Sywell, the engine audibly 'coughed' and then stopped. The flying pilot began searching for a suitable field for a forced landing.
Forced Landing and Damage
Most fields appeared newly ploughed, but the pilot identified a long field with a stubble surface, albeit not into wind. With insufficient height to maneuver for an into-wind approach, the pilot accepted a downwind landing at higher groundspeed than desired. The aircraft type lacks suspension and has disc brakes on the main wheels. As the pilot began gentle braking to avoid wheel lock, the nose dropped suddenly and the aircraft pitched forward, coming to rest upside down. The nosewheel had struck a tractor furrow before speed had reduced significantly, causing the nose landing gear to collapse. Both occupants vacated the aircraft unaided.
Post-Accident Findings
After recovery, fuel was drained from the wings: one wing was empty, the other contained a significant amount; no fuel leak was observed. The engine was connected to an external fuel source and started immediately, showing no signs of internal damage. This indicated that the engine failure likely resulted from a fuel supply interruption. The cause could not be positively determined, but possibilities include water in the fuel (for which there was no requirement or means to check) or air being drawn into the system when the fuel feed pipe became uncovered, as described in Service Bulletin SB131 (issued in 2012) which neither pilot was aware of. The aircraft's fuel tanks are interconnected but can feed unevenly during sideslip or turns, potentially uncovering the feed pipe if one tank empties first. The pilots had not reviewed the Service Bulletin, and it was not included in the aircraft's Pilot Operating Handbook.
Aircraft Information
The Flight Design CTSW is a high-wing, tricycle-undercarriage microlight constructed primarily from carbon fibre. Each integral wing fuel tank holds 65 litres (62 litres usable), gravity-fed. The maximum takeoff weight for a two-seat microlight with an airframe parachute system is 472.5 kg; G-KEVK was designed for 600 kg but limited by regulations. A subsequent weight and balance check revealed the aircraft was overweight due to extra safety equipment, although this did not affect the accident sequence. The Ballistic Recovery System fitted was not deployed, as the pilots deemed the field landing safer.
Conclusion
The engine failure, probably due to a fuel supply issue, led to a forced landing in a stubble field. The nosewheel striking a furrow caused the aircraft to invert; neither occupant was injured. Both pilots were unaware of a relevant Service Bulletin issued six years prior.