A RETURN LAND SITUATION WHEN ENG FIRE AND INFLT ENG SHUTDOWN CREATES NEED FOR AN EMER LNDG AFTER FUEL DUMPED.

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ACFT WAS A 4 ENG WDB WITH 363 PAX ABOARD; ABOUT 1/2 NON- ENGLISH SPEAKING. OAT WAS 79 DEG F; TKOF WT 734000 POUNDS; (MAX FOR THE ACFT). THE FIRST TKOF ATTEMPT WAS ABORTED AT ABOUT 80 KTS DUE TO A #1 ENG EGT GAUGE MALFUNCTION. THE GAUGE WAS REPLACED BY MAINT; AND SIGNED OFF IN THE LOGBOOK. THE BRAKE ENERGY CHART WAS CHKED; AND THE BRAKES WERE ALLOWED TO COOL FOR 1 1/2 HRS. (THE BRAKES WERE INSPECTED BY ALL 3 CREW MEMBERS INDIVIDUALLY; AND SIGNED OFF BY MAINT BEFORE THE NEXT DEP.) THE SECOND TKOF WAS NORMAL THROUGH FLAP RETRACTION AND REDUCTION TO CLB PWR; WHEN THE #4 ENG FIRE WARNING SOUNDED. ENG FIRE CHKLIST WAS CALLED FOR; AND FUEL DUMP WAS STARTED. BOTH FIRE BOTTLES WERE DISCHARGED; BUT THE FIRE WARNING LIGHT REMAINED ON. APCH CTL WAS ADVISED THAT WE HAD A #4 ENG FIRE WARNING; AND THAT WE WERE RETURNING TO SEA. WE DECLARED AN EMER; AND REQUESTED THAT THE EQUIP BE STANDING BY. 2 ADDITIONAL COCKPIT CREW MEMBERS WERE DEADHEADING ON THE ACFT. THEY WERE REQUESTED TO COME TO THE COCKPIT IMMEDIATELY. ONE BRIEFED THE CABIN CREW ON THE POSSIBILITY OF AN EVAC; THE OTHER VISUALLY CHKED THE #4 ENG FOR SIGNS OF FIRE. AS NO FLAMES OR SMOKE WERE VISIBLE; I ASSUMED THAT THE FIRE WAS OUT; AND PLANNED TO DUMP FUEL DOWN TO NEAR MAX CERTIFIED LNDG WT (585000 POUNDS ON THIS ACFT) AND ATC WAS SO ADVISED. THEY HAD OFFERED 3000 FT MSL; AND HOLDING N OF THE ARPT TO DUMP. WE REQUESTED; RECEIVED; AND CLBED TO 5000 FT AND OPTED TO HOLD S TO FACILITATE AN EARLY APCH TO RWY 34R AT SEA. ABOUT 1 1/2 MINS LATER THE #4 GENERATOR BEARING FAILURE LIGHT CAME ON; FOLLOWED BY THE #4 STARTER VALVE OPEN LIGHT. WE WERE THEN ADVISED BY ONE OF THE DEADHEADING CREW MEMBERS THAT A YELLOW GLOW WAS NOW VISIBLE THROUGH ONE OF THE #4 ENG BLEED PORTS. WE THEN ASSUMED THAT WE STILL HAD A LIVE FIRE; AND ADVISED ATC OF OUR INTENTION TO PUT THE ACFT ON THE GND AS SOON AS POSSIBLE. THE GEAR HAD BEEN LOWERED EARLIER FOR INCREASED DRAG TO INCREASE OUR FUEL BURN; AND FOR ADDITIONAL COOLING. WE LANDED ON RWY 34R AT SEA; AT 636000 POUNDS; 51000 POUNDS OVER MAX CERTIFIED LNDG WT. TWR ADVISED ON LNDG ROLL THAT FLAMES WERE VISIBLE ON THE #4 ENG. (FALLING HOT METAL PARTS FROM THE ENG ALSO IGNITED A SMALL GRASS FIRE JUST SHORT OF THE APCH END OF 34R.) THE LNDG WAS SMOOTH; NO TIRES WERE BLOWN; AND WE BRAKED TO A STOP ABEAM THE FIRE TRUCKS. THE EMER EVAC CHKLIST WAS COMPLETED; AND WE EVAC THE ACFT FROM THE L SIDE ONLY. THE 5L DOOR WOULD NOT FULLY OPEN; AND THAT EVAC SLIDE WAS NOT DEPLOYED. IT TOOK THE FIRE DEPT ABOUT 4-5 MINS TO EXTINGUISH THE BURNING MAGNESIUM ON #4 ENG. MANY PAX TRIED TO TAKE THEIR CARRY- ON BAGGAGE WITH THEM DOWN THE SLIDES; INCLUDING 1 MAN READY TO EXIT WITH A VIDEO CAMERA IN 1 HAND; AND A BABY IN THE OTHER. THE FIRE DEPT WAS NOT AWARE OF THE ENG BEING ON FIRE UNTIL TWR ADVISED ON ROLLOUT THAT FLAMES WERE VISIBLE. OVERWT LNDG HAD NOT BEEN PART OF THE COMPANY'S SIMULATOR TRAINING PROGRAM. WE HAD NOT LEARNED IN TRAINING THAT A LARGE AMOUNT OF MAGNESIUM IS USED IN THE ACCESSORY SECTION OF THESE ENGS; WHICH LEFT US UNAWARE OF A LARGE SOURCE OF COMBUSTIBLES OTHER THAN FUEL; OIL; ETC.