What was found
SYD - FLT 0909 - NR 1 ENGINE EXPERIENCED COMPRESSOR STALLS AT 37,000 FEET AFTER DEPARTING SYD. THE NR 1 ENGINE WAS SHUT DOWN AND THE AIRCRAFT WAS RETURNED TO SYD WHERE IT LANDED WITHOUT INCIDENT. MAINTENANCE READIED THE AIRCRAFT FOR FERRY FLIGHT TO GUM WHERE THE NR 1 ENGINE WILL BE REMOVED AND REPLACED. SUPPLEMENT - THE STALLS WERE CAUSED BY HIGH PRESSURE BLEED AIR REVERSE FLOW INTO THE 8TH STAGE BLEED AIR DUCT. THE ENGINE WAS NOT DAMAGED, IT WAS REMOVED AS A PRECAUTION FOR POST-STALL BORESCOPE. IT IS BELIEVED THAT FAILURE OF 1 OR ALL 3 OF THE FOLLOWING COMPONENTS COULD HAVE RESULTED IN THE REVERSE FLOW CONDITION: LOWER PRESS CHECK VALVE, PRESS REGULATOR VALVE, AND FAN REVERSER OVERPRESS VALVE. (W)