What happened
During a scheduled test flight following an engine change, a Twin Otter departed from runway 07 at Shoreham-by-Sea Airport under favorable weather conditions. While the initial climb appeared standard to observers, intermittent plumes of dark smoke were noted emanating from the right-hand engine. At an altitude of approximately 600 feet, the aircraft experienced a right-wing roll, subsequently inverted, and entered a spin that terminated in a ground impact near the River Adur. The aircraft struck the western flood bank of the river at a steep downward angle with significant yaw and roll. Following the impact, a large fire broke out, destroying much of the wreckage. There was one fatality involving the pilot, who was the only person on board.
Findings
Investigations into the wreckage revealed that both engines were still rotating at the time of impact, though the left engine was producing higher power than the right. Analysis of the flight controls indicated the rudder was positioned fully to the left and the elevator was in a full-up position. While the left engine showed no mechanical defects, investigators discovered severe corrosion within the fuel control boost capsule of the right engine. Laboratory testing confirmed that a perforation in this specific component causes power fluctuations and can lead to a rich cut during throttle adjustments. This mechanical failure was identified as the primary factor leading to the loss of control.