What happened
On 9 October 2005, a Thorp T-18, registration G-BSVN, was conducting a test flight from Ashcroft Airfield in Cheshire. The flight was being performed to verify the functionality of a newly installed air/oil separator. While leveling at 2,500 ft, the pilot observed oil spots accumulating on the windscreen. To address the issue, the pilot decided to return to the airfield immediately.
During the final approach to the grass Runway 2 and 7, the pilot became focused on the increasing oil contamination on the windscreen. At approximately 50 ft above the ground, the left wing dropped suddenly. The pilot noted an airspeed indication of roughly 60 kt and attempted to apply power and aileron input. However, the aircraft continued its descent and struck a farm field approximately 50 m short of the runway threshold. The impact caused damage to the undercarriage frame, the fuselage bulkhead, and the propeller. The pilot escaped the aircraft without injury.
The investigation
The investigation examined the aircraft's recent maintenance history and the mechanical state of the engine components. It was noted that a replacement air/oil separator had been installed and secured with jubilee clips during recent maintenance to renew the aircraft's Permit to Fly. Following the accident, the owner observed that the return oil pipe from the air/oil separator had become detached. While it could not be confirmed if the detachment happened during the flight or prior to it, the owner reported no previous issues of this nature.
Findings
- The pilot's attention was diverted by the need to land immediately due to the oil on the windscreen.
- The airspeed decayed to a level that caused the left wing to stall.
- The application of power and right aileron input likely worsened the wing drop.
- The aircraft was not equipped with stall strips, which can make the stall characteristics of this type less predictable.