Shortly after take-off, the crew of the Boeing 747 aircraft received a number four engine fire warning advisory. The crew actioned the non-normal checklist, secured the number four engine, and discharged two engine fire bottles before the fire indication extinguished. The crew then jettisoned fuel and completed an uneventful landing at the departure airport.
Initial inspection by operator maintenance personnel revealed evidence of charring and discolouration around the engine combustion area. Maintenance personnel removed the engine from the aircraft and the engine was then test run on an engine test cell. The test run revealed a fuel leak from the left and right fuel manifold connectors. The connectors were confirmed as being secured with safety lockwire, but subsequent torque checks revealed a lower value of torque than that required by the engine manufacturer's maintenance manual. The fuel manifold connectors were re-torqued and another test run completed. The resulting test run at high power settings revealed no discrepancy. A decision was made by the operator to have the engine overhauled before being put back into service.