What was found
RTFL DUE TO NR 1 ENGINE SURGE. ENGINE SURGED IN CRZ APPROX 2-1/2 HRS OUT FROM IAD EN ROUTE MUC. DECISION TO RETURN TO IAD. AFTER LDG, IAD MM FOUND METAL IN TAILPIPE. ENG REPLACED AT IAD. [08-14-07] TEARDOWN REVEALED THAT 4 LP TURBINE TRANSITION DUCTS (PW IPC 72-30-00-002-250, P/N 50M919) HAD EXPERIENCED EXTREME INNER FOOT WEAR. THIS CAUSED A LOSS OF RADIAL RETENTION AT THE FRONT OF THE DUCT, ALLOWING DUCTS TO DEFLECT INWARDS INTO PRIMARY GASPATH, AND DISTORTING GASPATH FLOW INTO THE LP TURBINE, RESULTING IN SURGE. UA HAS SEEN FOOT WEAR AT TEARDOWN, BUT NEVER TO THIS EXTENT. PARTS HAVE BEEN RETURNED TO MANUFACTURER & MTU FOR FURTHER ANALYSIS.