History of the Flight
The aircraft, a Piper PA-28-140 Cherokee (G-AZWE), departed from Netherthorpe's Runway 06 at 1400 hrs on 31 August 2005. There was no headwind and the outside air temperature was 29°C. After rotation, the aircraft became airborne but then sank back onto the runway with the airspeed stagnating. It crossed the airfield boundary, with the throttle closed, and hit a stone wall approximately 75 m beyond the runway's end, rendering both occupants unconscious. The aircraft did not catch fire.
The pilot and his passenger, another qualified pilot, had planned a day's flight from their home base at Dunkeswell. They had landed at several airfields before arriving at Netherthorpe. After refuelling to full tanks at Turweston Airfield, they departed for Netherthorpe. Their first approach to grass Runway 06 resulted in a go-around as the pilot considered the speed slightly too fast. They landed on the second approach and took lunch in the clubhouse. The acting Chief Flying Instructor at Netherthorpe suggested using Runway 06 for departure due to a downhill slope, which they accepted.
Performance
The exact weight at the time of the accident could not be determined but was likely close to maximum weight of 2,150 lbs when departing Turweston, and approximately 2,100 lbs at Netherthorpe. The grass runway was firm with grass 2-3 inches long, cut the morning after the accident to about 1½ inches. The manufacturer's flight manual provides takeoff performance data for a takeoff with full throttle, flaps retracted, and lift-off initiation at 73 mph. CAA Change Sheet No 3 Issue 1 states that the aircraft fails to achieve the performance scheduled in Section V of the flight manual and offers correction data to the Takeoff Distance Required (TODR). TODR is defined as the distance required from the start of the take-off run until the aircraft achieves a height of 50 ft.
Netherthorpe Airfield is 250 ft amsl. The surface wind was 150°/10 kt and temperature 29°C. Considering the downslope of 1.9% on Runway 06, the performance table suggests a TODR of 856 m. The manual notes that the take-off run must be taken as 55% of the TODR, i.e., 471 m, which has been factored by 1.15, so the calculated take-off run with no safety factors would be 409 m. Runway 06 has a total length of 553 m and a Takeoff Run Available (TORA) of 476 m. The TORA finishes 77 m from the end of the runway. The flight manual gives no guidance for short field take-off technique or performance figures for flap settings other than retracted.
Given the aircraft's configuration, weight, weather, and runway conditions, there was insufficient take-off run available for the aircraft to become safely airborne.
Aircraft Information
The aircraft was manufactured in 1972 and last received a star annual inspection on 17 June 2005, at which time it had accumulated 13,071 flying hours. At the accident, it had 13,144 hours. The last 50-hour inspection was on 9 August 2005 at 13,118 hours. No defects or rectifications were recorded in the log books since that inspection.
Examination of the Accident Site and Wreckage
Ground marks from the landing gear extended from the end of the runway to the boundary fence and across the adjoining field. The aircraft tracked slightly left while yawing right near the end of the runway, then passed through the boundary fence, striking a fence post and hedge with the left wingtip, initiating a significant yaw to the left. The left yaw reduced but the track continued until impact with a stone wall approximately 275 ft from the end of the grass at the edge of the airfield. The final track was approximately 045°M and final heading approximately 035°M.
Examination showed no major pre-accident defects in structure, flight controls, or engine. The aircraft was configured with flaps retracted. The engine was turning under low power at impact. Initial contact was made by the left wing tip, which detached and swung the aircraft further left before the propeller struck the wall. The cabin remained intact, seats secured. The passenger's diagonal harness had pulled out of the structure due to overload; other belts and harnesses were undamaged and functioned as intended. The fuel, magnetos, and battery master switch were turned off shortly after the accident; throttle and mixture controls were moved during impact or evacuation. The engine tachometer jammed at about 650 rpm, consistent with idle power at impact. The airspeed indicator was accurate within 1 mph between 74 and 40 mph but had an old-style presentation making confusion of knots and mph scales easy. The aircraft carried a GPS but it was not recording during the takeoff.
The left fuel tank was ruptured by the wall; the right tank drain valve sheared off. A considerable quantity of fuel drained from the aircraft.
Netherthorpe Procedures
The CAA's Aeroplane Performance Safety Sense Leaflet 7c quotes Article 43 of the Air Navigation Order, stating the pilot-in-command must ensure adequate performance. The leaflet notes that performance data checks may not be necessary if sufficient runway is available. Netherthorpe is a licensed airfield with one of the shortest available take-off and landing distances in the UK. Performance margins for certain light aircraft can become very small.
The pilot had noted the runway length as 553 m but was not aware of the TORA of 476 m. He had a personal limit for runway operations of 500 m based on experience. Prior to arrival, neither pilot had checked the performance figures from the flight manual, a procedure they had not carried out since basic training. The aircraft was unusually heavy due to full refuelling, and the ambient temperature was unusually high. The difficulty experienced at Turweston, a longer paved runway, should have indicated performance concerns.