Air Accidents Investigation Branch
After landing the crew started the APU and transferred the aircraft systems to be powered by the APU generator. When the APU generator was transferred to the right bus, the R61 contactor for the forward galley failed, emitting a noise, a flash and fumes. The crew discharged a fire extinguisher towards the source. The associated circuit breaker (CB) had opened, isolating the R61 contactor.
Assessment of the contactor did not determine the cause of its failure, but it is likely that either loose connectors on the input terminals, or loss of hermitic sealing of the unit caused the event. As the associated CB opened after the failure, it is considered that protection systems operated normally on the aircraft. The use of the fire extinguisher by the crew was an appropriate response based on the information available to them at the time, although the failure was contained without this intervention.