History of the flight
The aircraft was refueled to the tabs at Blackbushe Airport, receiving approximately 30 US gallons of fuel. The pilot and one passenger flew to Belle Vue Farm, Devon, to pick up two friends and return to Blackbushe. The outbound flight and landing were uneventful, taking about one hour. No additional fuel was taken at Belle Vue Farm. The pilot collected the passengers and taxied for takeoff on Runway 08, which had a damp grass surface, a length of 625 meters (2,050 feet), and an elevation of 675 feet amsl. A hedge and fence bordered the eastern end of the runway. Weather was clear with cloud at 2,500 feet and a surface wind estimated at 5 knots from the north.
The pilot considered the takeoff normal, with the aircraft becoming airborne about two-thirds along the runway. After lift-off, he leveled the aircraft at 20 to 25 feet intending to accelerate before climbing over the hedge at the runway end. During the level acceleration, a short distance before the hedge, the aircraft dropped back onto the ground. Realizing the impossibility of stopping, the pilot pulled back on the control column and climbed over the hedge, clipping a fence post. The aircraft dropped into the next field; the pilot closed the throttle and attempted to stop. Seeing another hedgerow, he pulled hard back on the control column, and the underside of the aircraft struck an earth bank and the hedge. The nose came to rest in a ditch on the far side, with the fuselage broken aft of the cabin area. The front seat passenger, also a pilot, switched off the magnetos, master switch, and fuel. The aircraft did not catch fire.
Aircraft performance
The aircraft's maximum permitted takeoff weight is 1,054 kg. The exact weight at the time of the accident could not be determined but was estimated to be at or close to maximum. The flight manual's performance data indicates that at maximum weight under prevailing conditions, the aircraft would have required a takeoff run of 1,740 feet and a total takeoff distance to clear a 50-foot obstacle of 2,160 feet. This data assumes a dry level paved runway and includes a correction for airfield elevation but not for less favorable conditions.
The CAA publication General Aviation Safety Sense Leaflet 7B 'Aeroplane Performance' provides factors for different operating conditions. Using a factor of 1.2 for a dry grass surface, the takeoff distance to 50 feet would increase to 2,590 feet. The leaflet also recommends an additional safety factor of 1.33 for lack of practice, incorrect technique, aircraft and engine wear, and less favorable conditions, which would yield a required distance of 3,450 feet.
The owner's handbook advises: 'After take off let the aircraft accelerate to the desired climb speed by lowering the nose slightly.' The use of 25° flap is recommended for short or soft fields; the pilot reported he thought some flap was selected. He was surprised the aircraft dropped back onto the ground while attempting to accelerate. Possible reasons include the influence of ground effect: as a low-wing type, the aircraft's ground effect reduces induced drag up to about half the wingspan (17 feet for G-BTIH, with a wingspan of 35 feet). Additionally, a hangar at the northeastern corner of the airfield may have caused a local wind effect, such as a downdraft or tailwind in its lee, adversely affecting performance.
Injuries and rescue
All four occupants were wearing seatbelt lap restraints without shoulder harnesses, though harnesses were available for the front seats. All occupants received injuries and required assistance to exit. The pilot exited through the broken forward windscreen; the front and rear seat passengers had to be cut out of the aircraft. Two bystanders quickly arrived and called emergency services, who attended within a few minutes.