What was found
FLT 1556 EN ROUTE AT 26,000 FT, CAPTAIN FELT A YAW & HEARD A COMPRESSOR STALL COMING FROM RT ENGINE. ENGINE READINGS NORMAL. HOWEVER, A PASSENGER SAW FIRE COMING FROM RT ENGINE DURING STALL. CAPTAIN DECLARED AN EMERGENCY & FLT DIVERTED. DURING TAXI TO GATE, RT ENGINE OIL PRESSURE DROPPED & OIL TEMP CLIMBED TO RED. CREW SHUTDOWN RT ENGINE & TAXIED TO GATE WITHOUT FURTHER INCIDENT. MAINTENANCE REPLACED RT ENGINE. REPAIR SHOP REPORTED THE COMBINATION OF HEAVY SPALLING OF ATTRITION LINING OF HPC CASES & IOD OF HPC BLADES CAUSED REPORTED HPC SURGE. IOD CAUSED BY THE LIBERATION OF STAGE 2 LOCK PLATE.