History of the Flight
The aircraft, a Raytheon Beech Bonanza A36 (registration N4VQ), was taking off from Fenland Airfield's grass Runway 18 with the pilot and three passengers on board. The pilot held the nosewheel off the ground to prevent it digging in and slowing the aircraft down. About halfway down the runway the aircraft became airborne, earlier than expected. It touched down briefly before becoming airborne again. It then reached a height of about 15 to 20 feet and began to roll to the left, reaching an angle of about 45 degrees. The pilot shut down the power, levelled the wings and deployed full flap. He subsequently landed the aircraft, with the wings almost level, in a field beyond the runway before the aircraft came to an abrupt halt against a dyke. All four occupants disembarked safely, although the pilot sustained a minor injury.
Airfield Information
Fenland Airfield is a grass airfield at an elevation of 18 feet amsl. Runway 18 is 512 m long with a Take Off Distance Available (TODA) of 594 m. South of Runway 18 is a field bounded on its south by a dyke running perpendicular to the runway. The airfield also has another grass runway, 08/26, which is 670 m long.
Weather Conditions
The pilot reported that the condition of Runway 18 was soft and that the wind was from 220 degrees at 15 knots. A Met Office aftercast estimated the wind to be 220 degrees at 15 knots, with gusts possibly up to 22-25 knots.
Aircraft Performance
The aircraft takeoff roll and distance to 50 feet were calculated using the Pilot's Operating Handbook (POH) based on a takeoff mass of 3,600 lbs at sea level on a paved runway, with no flaps, and with the local weather conditions being 12 degrees Celsius and a 12 knot headwind component (as reported by the pilot). The unfactored distances specified in the POH are: takeoff roll 335 m, distance to 50 ft 579 m. Applying a factor of 1.25 for soft ground gives: takeoff roll 419 m, distance to 50 ft 724 m. With the recommended Public Transport factor of 1.33: takeoff roll 557 m, distance to 50 ft 963 m. The CAA's Aeronautical Information Circular (AIC) 67/2002 specifies that 25% or more be added for soft ground, and strongly recommends an additional 33% factor. The unfactored distances were achieved by the manufacturer in ideal conditions.
Aircraft Handling Characteristics
The aircraft manufacturer confirmed that the Beech Bonanza A36 will yaw to the left and then roll to the left after leaving the ground if insufficient right rudder is used to compensate for the propeller slipstream effect. They also noted that the situation can initially be compounded if right aileron, rather than right rudder, is used to counteract the turn, due to adverse aileron yaw.
Analysis
In the reported conditions, the aircraft would be expected to lift off after 419 m and be at 50 ft after 724 m. On Runway 18 at Fenland, the aircraft would be at around 30 ft at the end of the available takeoff distance, assuming a 1.25 factor for soft ground. The wind was from 220 degrees; a better option would have been to use Runway 26, which was 670 m long. While the aircraft was capable of taking off from Runway 18, the margins were small. The aircraft lifted off too early and, as a result, was at too low an airspeed and possibly at too high an angle of attack. In such a situation it would not accelerate normally and, close to the stall, a wing drop, as described by the pilot, could readily occur. The pilot had only 20 hours on type, and this may also have been a factor.