What happened
On 12 December 1997, a Cessna F150H, registration G-AVVX, was attempting a takeoff from Franklins Field, a private grass airstrip located near Wells, Somerset. The pilot intended to utilize the downward slope of runway 23 to assist the departure, configuring the aircraft with 5° flaps. After applying full throttle and releasing the brakes, the aircraft accelerated to approximately 55 mph by the end of the downhill section. However, the aircraft failed to gain further speed, leaving insufficient runway remaining to complete the takeoff or stop safely.
As the aircraft approached the boundary fence, the pilot attempted to lift the nose to clear the obstacle. The main landing gear struck the top of the fence, triggering the stall warning. Seeking to avoid further impact, the pilot opted to land in an adjacent ploughed field. Upon contact with the soft, furrowed ground, the aircraft dug into the earth and overturned onto its back. There were no injuries to the two occupants on board.
The investigation
Investigators examined the strip conditions and the aircraft's performance capabilities. The airfield, a 570 by 17-metre grass strip, features a significant downslope on runway 23. The pilot suggested that a patch of unusually soft ground located between the end of the slope and the end of the runway created excessive drag, preventing the aircraft from reaching a safe unstick speed.
Analysis of the aircraft's weight revealed that with a payload of 448 lb and an estimated empty weight of 1100 lb, the aircraft was operating near its maximum takeoff weight. While the published ground roll for this weight on tarmac is 224 metres, the investigation considered the impact of the strip surface. It was determined that while the ground was soft, there should have been enough runway length for a successful takeoff had the drag not been so significant.