History of the Flight
The aircraft, a Jabiru UL-450 registered G-CEKM, was on a private flight from Cromer to Headon. The pilot made a long final approach from 3 nm east of Headon, commencing a descent from 1,500 ft QFE with the engine speed set at approximately 2,000 rpm. Both heater elements of the electric carburettor heat were selected on for the entire flight, and the pilot selected the ‘hot air’ carburettor heat to on for approximately 10 seconds at the start of the descent. During the descent, the aircraft passed within 300 to 400 metres of an operational power station located south-east of Headon, near the river Trent. At approximately 300 ft QFE, the pilot increased the throttle setting, but the engine failed to respond. He selected the ‘hot air’ carburettor heat to on and shortly thereafter the engine stopped. The aircraft touched down short of the intended field and struck a hedge bordering the field. The nosewheel then entered a ditch, causing the aircraft to pitch over inverted. The pilot shut down the aircraft and switched off the fuel. Both he and the passenger were uninjured and exited the aircraft after kicking out the passenger window.
Aircraft Examination
The pilot inspected the aircraft and found no anomalies with the fuel system. However, a wire to the electric carburettor heat system was found to be broken, rendering it inoperative. The pilot considered that it was unlikely to have broken in the forced landing and concluded that the electrical carburettor heat was probably not working during the latter stages, and possibly all, of the accident flight.
Atmospheric Conditions
The aftercast supplied by the Met Office is included in Table 1. From the chart in Figure 1 it can be seen that the general conditions were favourable for ‘light icing - cruise or descent power’. As reported in AAIB Bulletin 4/2003, in which a Jabiru UL-450 G-TYKE suffered a loss of power after being flown close to a power station, the humidity of the air can be significantly raised over a considerable distance from cooling towers, depending on the wind speed and level of turbulence. This can create local conditions more favourable for serious carburettor icing.
Discussion
The most likely reason for the engine failure was carburettor icing. The failure of the electrical lead to the electric carburettor heat and the proximity of the power station were considered to be significant factors. The pilot routinely flew with the electrical heat on at all times. If it had failed, his brief use of the ‘hot air’ carburettor heat may not have been effective in preventing carburettor icing.
Table 1: Atmospheric conditions at various heights AGL (Wind direction & speed, temperature, dew point, humidity) were recorded from the surface to 2000 ft.