What happened
On 10 October 2013, a Beech B200C Super King Air, registration G-SASD, was performing a commercial air transport mission as an air ambulance. The flight was traveling from Lerwick to Aberdeen Airport, carrying a crew of two and three passengers, including one patient on a stretcher.
During the landing sequence at Aberdeen, the aircraft made a normal touchdown. The pilot initially applied full reverse thrust; however, as the aircraft approached the E3 exit, it began to drift toward the right. The pilot noted that the aircraft was failing to decelerate at the expected rate. Consequently, the aircraft veered off the paved surface and onto the grass, coming to a stop after traveling approximately 50 metres. There were no injuries to the crew or passengers, though both left main gear tyres sustained damage.
The investigation
Following the incident, engine ground runs were conducted on the aircraft. During these tests, the left engine demonstrated an immediate acceleration to maximum torque. This led investigators to focus on the left engine's Fuel Control Unit (FCU).
Upon replacement of the FCU, the original component was sent to the manufacturer in Quebec for examination. The disassembly was performed alongside a representative from the Transportation Safety Board of Canada. The investigation revealed that debris was obstructing the Py orifice within the unit. This obstruction caused an increase in fuel flow, which matched the behavior observed during the runway excursion.