scope:

Description of Driving Event:

APU 2 Fuel Pump Heater was cycling high during flight. Detailed analysis of the thermal switch showed extreme wear from the switch bi-metal disc and case. Large amounts of conductive contaminates were found. Analysis showed that they came from the disc and case. It is concluded that excessive vibration caused the wear and in zero gravity particles were free to migrate into the electrical contacts, resulting in a higher disc deflection to open the thermostat contacts. The result is a higher heater turn off temperature.