Beech 200 Super King Air G-BYCP was planned to operate a non-commercial flight from Stapleford Aerodrome to RAF Brize Norton with two company employees on board to pick up two passengers for onward travel. The captain occupied the left seat and another pilot occupied the right. The second occupant worked for the operator of G-BYCP but his license was valid on Bombardier Challenger 300 and Embraer ERJ 135/145 aircraft and not on the King Air. The planned departure time of 08:15 hrs was delayed because of poor meteorological visibility. The general weather conditions were fog and low cloud with a calm wind. At approximately 08:50 hrs the visibility was judged to be approximately 600 m. At approximately 09:15 hrs the visibility was at least 1,000 m and the pilot decided that conditions were suitable for departure. The planned departure was to turn right after takeoff and intercept the 128ø radial from Brookman’s Park VOR (BPK) heading towards the beacon, and climb to a maximum altitude of 2,400 ft amsl to remain below the London TMA which has a lower limit of 2,500 ft amsl. The aircraft took off at 09:21 hrs and was observed climbing in a wings level attitude until it faded from view shortly after takeoff. After takeoff, the aircraft climbed on a track of approximately 205øM and, when passing approximately 750 ft amsl (565 ft aal), began to turn right. The aircraft continued to climb in the turn until it reached 875 ft amsl (690 ft aal) when it began to descend. The descent continued until the aircraft struck some trees at the edge of a field approximately 1.8 nm southwest of the airport. The pilot and passenger were both fatally injured in the accident, which was not survivable. Conclusion: Examination of the powerplants showed that they were probably producing medium to high power at impact. There was contradictory evidence as to whether or not the left inboard flap was fully extended at impact but it was concluded that the aircraft would have been controllable even if there had been a flap asymmetry. The possibility of a preaccident control restriction could not be discounted, although the late change of aircraft attitude showed that, had there been a restriction, it cleared itself. The evidence available suggested a loss of aircraft control while in IMC followed by an unsuccessful attempt to recover the aircraft to safe flight. It is possible that the pilot lost control through a lack of skill but this seemed highly unlikely given that he was properly licensed and had just completed an extensive period of supervised training. Incapacitation of the pilot, followed by an attempted recovery by the additional crew member, was a possibility consistent with the evidence and supported by the post-mortem report. Without direct evidence from within the cockpit, it could not be stated unequivocally that the pilot became incapacitated. Likewise, loss of control due to a lack of skill, control restriction or distraction due to flap asymmetry could not be excluded entirely. On the balance of probabilities, however, it was likely that the pilot lost control of the aircraft due to medical incapacitation and the additional crew member was unable to recover the aircraft in the height available.