After lift-off at 85 knots, the pilot noted a positive rate of climb before retracting the landing gear and flaps. He then felt the aircraft sink and noted a high indicated rate of descent. Although full power was applied the descent continued until the aircraft struck the runway in a slightly nose-up attitude. The aircraft slid across the overrun area and through a fence before coming to rest. Fire broke out and engulfed the wreckage. At the time of the accident the aircraft weight was more than 200 kg above the maximum allowable and the centre of gravity was 142 mm forward of the forward limit. The pilot had been unable to retain control of the aircraft during the initial climb phase when the flaps were retracted at a relatively low airspeed.