Electrical Fault Caused Fuel Imbalance
Cessna Citation 680, Bedfordshire, UK, Sept. 30, 2010–While en route from London Luton Airport to Milas, Turkey, the Sovereign suffered a left main bus electrical system fault that prompted the crew to return to Luton. Upon examination, the twinjet’s left main fuel tank was found to be full with 5,500 pounds of fuel while the right tank contained 3,300 pounds. The UK’s Air Accidents Investigation Branch, which is conducting the investigation, issued a bulletin stating the incident showed that “removal of power from the left main bus will cause the fuel cross-feed valve to open and the right boost pump to operate without any crew selection, and the motive-flow shutoff valves will remain open. This allows motive-flow fuel to be returned to both tanks, resulting in uncommanded fuel transfer from the right to the left tank.” During the 20 minutes of flight before the Citation landed at Luton, enough fuel was transferred from the right to left tanks to create a 2,200-pound imbalance.