What was found
JFK-ORD - AIR TURNBACK, AT 10,000 FEET WITH CRUISE POWER, LOUD BANG AND BUMP. NR 1 ENGINE EGT CLIMBED TO 850 DEGREES AND NACELLE TEMPS TO 4.5 BLEED VALVE CLOSED. EGT CONTINUED ABOUT 100 DEGREES ABOVE OTHER ENGINES. SAW T/R BLOW-OUT PANEL OPEN. RETURNED TO JFK. NO FUEL DUMPED. FOUND INTERMEDIATE CHECK VALVE, Y-DUCT AND ELBOW FAILED. REPLACED CHECK VALVE PER MM 36-11-02. REPLACED DUCT ASSEMBLY P/N 65B94819-2 PER MM 36-11-01. LEAK CHECK OK. REPLACED MANIFOLD P/N 1756M94603 PER MM 36-11-00. REPLACED TUBE ASSEMBLY 9057M85G02 PER MM 36-11-00. OPS AND LEAK CHECK OK. (M)