What happened
On 24 March 2016, a Socata TB9, registration G-BTWX, was performing a private flight from a farm strip near Jericho Farm, Lambley. The pilot had been monitoring local weather and ground conditions for several weeks, waiting for suitable flying conditions. On the day of the accident, the pilot noted increasing winds and decided to attempt a takeoff after the wind reached approximately 225° at over 20 knots.
Due to soft ground at the start of the westerly runway, the pilot utilized 540 metres of the available 580 metres. During the takeoff roll, the aircraft reached 50 KIAS halfway along the strip. As the aircraft became airborne, the pilot noticed a reduction in acceleration and elected to fly level to build airspeed. During this phase, the pilot observed a van travelling along the road adjacent to the airfield. Fearing a collision, the pilot attempted to climb the aircraft at a low airspeed. This maneuver caused the right wing to drop, striking the van and subsequently detaching from the aircraft. The remaining fuselage crossed the road and came to a halt in a nearby field. There were no injuries to the pilot or the driver of the van.
The investigation
The AAIB examined the pilot's performance calculations and the airfield conditions. The investigation established that the pilot had calculated the takeoff distance required (TODR) based on ground roll performance data. The pilot applied several variables to his calculation, including adjustments for uphill slope, soft ground, humidity, and engine wear, and further reduced the required distance using a personal 'rule of thumb' based on the headwind component.
However, the investigation found that the pilot's calculations focused on the ground roll rather than the distance required to clear a 50 ft obstacle, which would have been more appropriate given the proximity of the hedge and the road. Furthermore, the pilot did not account for the factor of short dry grass.
Findings
- The pilot's calculated takeoff distance was based on ground roll rather than the distance needed to clear a 50 ft obstacle.
- The pilot's calculations failed to include a safety factor for short dry grass.
- If the grass factor had been included, the required distance would have exceeded the available runway length.
- The available distance was inadequate for the intended climb to clear the obstacle.
- The aircraft was damaged beyond economic repair.