While at approximately 8,000 ft after departure from Sydney, the crew heard a loud bang from the left side of the aircraft. The number 1 engine pressure ratio (EPR) had dropped slightly while the compressor speed (N1), exhaust gas temperature and fuel flow indications increased. The engine vibration level remained within limits. A flight attendant reported seeing something entering into or flaying around the engine intake. After discussions with ground maintenance, the aircraft was returned to Sydney, where an uneventful landing was made after about 50,000 kg of fuel had been jettisoned off the coast.
Examination of the engine by the operator revealed evidence of a bird strike. Blood was found on the engine fan exit nozzle, and the glass-reinforced plastic of the ice impact panel was damaged. About 90 per cent of the circumference of the ice impact panel that covered the acoustic liner aft of the fan was found to be missing
The fan was inspected for damage and the remains of the ice impact panel were removed. (The engine maintenance manual allows the ice impact panel to remain damaged beyond limits or missing for up to 125 hours, or until the next aircraft maintenance inspection.) The EPR probes and their lines were flushed clean and appropriate line connectors were replaced.
A subsequent engine ground run found EPR indications had returned to normal and the engine was cleared back to line operations.