What happened
On 24 May 2015, an SD-1 Minisport, registration G-CIMA, was attempting to depart from a private airstrip at Meldreth Valley Farm. The pilot initiated a takeoff into a light wind aligned with the runway. While the engine appeared to be operating normally and maintaining the required RPM, the aircraft failed to climb once it left ground effect. As airspeed decreased, the pilot was forced to perform an emergency landing in a field of tall crops located ahead of the runway. The impact with the vegetation resulted in minor injuries to the pilot, but the aircraft was damaged beyond economic repair.
The investigation
The investigation examined the aircraft's configuration and the environmental conditions at the time of the accident. The SD-1 Minisport is a single-seat ultralight with a tailwheel layout. Due to the specific engine installation on G-CIMA, the propeller and crankshaft axis are positioned lower on the fuselage, and the propeller diameter is smaller than other variants. This configuration results in limited slipstream effect on the high-mounted stabilator. The pilot noted that transitioning the aircraft from a high-drag, tail-down position to a low-drag, level attitude was heavily dependent on airspeed rather than engine power.
Investigators also reviewed the pilot's experience and the airfield's characteristics. The runway featured a 2% upslope. The pilot had previously noted marginal performance from this strip, but because the pilot also operated a different high-wing microlight with superior takeoff performance, there may have been a reduced awareness of the specific performance limitations of the SD-1.
Findings
Several factors contributed to the aircraft's inability to maintain flight after leaving ground effect:
- An increase in ambient temperature since the start of the flying season had caused a progressive reduction in engine performance.
- The wind direction on the day necessitated a takeoff in a direction opposite to the preferred downhill slope.
- The actual wind speed at the strip was lower than the wind speed reported in the nearby Cambridge weather reports used for planning.
- A delay in transitioning the aircraft from a high-drag tail-down position to a level fuselage position during the takeoff roll.
- Inadequate airspeed was achieved to sustain a climb out of ground effect.