History of the Flight
The pilot had landed the Piper PA-15 Vagabond, registration G-BOVB, at Whitefield's Farm during the afternoon following an uneventful flight from South Molton Airfield. After visiting the farm house with his passenger, he prepared for a short onward flight to Eaglescott Airfield. The pilot had previously visited the field by car to assess its suitability and checked it again on foot prior to departure. The field, at an elevation of 600 feet, is approximately 320 metres in length between a farm drive and a hedge, bounded on its northern side by trees and woodland. The available take-off direction is east-west, with a slight upslope followed by a marked downslope when taking off to the east, as the pilot intended. Weather reports were obtained from Exeter and Bournemouth Airports, timed at 1500 hrs, reporting a surface wind from the north-west, good visibility but with rain showers, and cloud between 2,000 and 2,500 feet. The pilot estimated the surface wind at the farm to be from the north at 5 kt and observed an isolated shower about 3 nm north of the farm. Surface temperature was estimated to be 8°C.
The pilot started the engine and taxied along the strip over damp grass. There was 16 kg of fuel on board, a mixture of AVGAS and MOGAS in an approximate ratio of 4:1. While taxiing, the pilot applied carburettor heat for between 20 and 30 seconds. Power checks and take-off checks were completed with no abnormalities, and the pilot applied carburettor heat for approximately 10 seconds as required by the checklist. The aircraft was not equipped with wing flaps.
The takeoff initially appeared normal, with satisfactory acceleration as the aircraft passed 50 mph airspeed. The pilot considered take-off performance normal. Soon after becoming airborne, the pilot sensed that the aircraft was not climbing as it should. The rate of climb reduced to a gradual rate of descent, causing the aircraft to fly parallel to the sloping field. Beyond the take-off field was a further large field, and the pilot decided to carry out a forced landing into it. However, the aircraft did not clear the hedge at the end of the take-off field, striking the upper part of the hedge with its main wheels. The aircraft pitched forward and landed on its main wheels in the field beyond. The propeller struck the surface, and the aircraft continued to pitch forward until it inverted, sliding for a short distance. The pilot and passenger sustained cuts and bruises but were able to vacate the aircraft through the right-hand door. Both seats maintained integrity, and the lap straps and diagonal harnesses prevented more serious injuries. However, the fire extinguisher had detached from its mounting bracket, causing damage to the discharge nozzle that would have prevented its use. There was no fire, but fuel was seen leaking from the filler cap. As a precaution, the pilot called the fire brigade, who arrived soon after with the police and ambulance service. The aircraft sustained extensive damage and was subsequently written off.
Meteorological Information
An aftercast was obtained for the Whitefields Farm area for the time of the accident. The 2,000 feet wind was from 360°(M) at 15 to 20 kt, and the 1,000 feet wind was from 360°(M) at 15 kt, giving a likely surface wind from 350°(M) at 7 to 12 kt. Visibility was 20 to 30 km, reducing to 10 km in showers. There was scattered cumulus cloud at 2,000 to 2,500 feet, increasing in amount in showers. The surface temperature was 11°C, and the dew point was 7°C, giving a humidity of 76%.
Analysis
The pilot provided a detailed report and considered possible causes. He did not recall any unusual engine noises or changes of engine note during takeoff. Fuel contamination was unlikely, as samples taken before and after the accident were clear, and the previous flight had not shown any symptoms. The pilot and passenger both recalled the airspeed check at 50 mph; as the initial climb-out speed is 55 to 60 mph, the pilot thought it unlikely that the aircraft became airborne at a significantly slower speed. He did not recall any unusual control requirements and did not believe the aircraft was close to the stall when it first became airborne.
The throttle control was still fully open after the accident, and the friction control nut was tight. The engine showed no obvious signs of internal mechanical failure. The weight and balance of the aircraft were within prescribed limits.
The northerly wind, combined with large trees to the north of the field, suggested possible unusual local wind effects that may have adversely affected performance. However, the pilot's own estimate of surface wind was close to the aftercast wind, and although there was a possibility of a slight tailwind, the conditions were unlikely to have exceeded the aircraft's performance capabilities.
The combination of temperature and dew point indicated a 'serious' icing risk at all power settings, further increased by the damp grass. The pilot reported that the aircraft had been stationary with the engine running in a wetter area at the side of the field, also increasing the risk. The use of MOGAS further increases the risk of carburettor icing due to its increased volatility and higher water content. Given the prevailing conditions, the carburettor heat application before takeoff may not have been sufficiently long to completely clear any ice that may have formed. The pilot and others who flew the aircraft regularly had only infrequently encountered carburettor icing in this aircraft. However, in the absence of other evidence, the possibility that carburettor icing caused a loss of power on takeoff cannot be ruled out.