Incident Overview
During an approach to landing, the flight data recorder indicated that as the aircraft descended through 2,875 feet pressure altitude, the number 2 engine fuel flow increased, followed by a rise in exhaust gas temperature (EGT). The engine's N1 speed, initially at 25.6 percent, decreased to 12.8 percent. The crew performed an engine cutoff 74 seconds after the fuel flow increase began. The aircraft subsequently made an uneventful landing.
Examination Findings
Post-incident examination of the number 2 engine revealed a broken wire in the electronic engine control's hydromechanical unit, specifically the fuel metering valve resolver Channel B. The wire break was attributed to damage incurred during the manufacturing process. This damage caused unstable Channel B sine out voltage when the resolver was heated above 160 degrees Fahrenheit.
System Response
The fuel control computer software locked on Channel B, disabling Channel A. Due to the unstable sine out voltage, the computer commanded the fuel metering valve to a full open position. The resulting large increase in fuel flow, with the engine at idle speed, caused the engine core to stall and produced heat damage to the low pressure turbine.