B777 IS UNABLE TO COMPLETE AN ETOPS FLT DUE TO MECHANICAL PROBS. FUEL IS JETTISONED FOR RETURN AND LNDG AT DEP STATION.

Narrative

FLT HAD A NORMAL DEP. SHORTLY AFTER LEVELING OFF; W OF TOU AT INITIAL ASSIGNED ALT OF FL320 WE RECEIVED AN EICAS MESSAGE 'PACK L?' WE FOLLOWED THE ELECTRONIC CHKLIST; WHICH INDICATED A L PACK OVERHEAT AND L PACK SHUTDOWN. THE CHKLIST ENDED BY REQUIRING THE L PACK TO BE TURNED OFF. WE INITIATED A CALL TO DISPATCH AND HAD THEM PATCH US THROUGH TO MAINT CTL. MAINT CTL LED US THROUGH SOME TROUBLESHOOTING ROUTINES THAT A) WHILE THEY WERE NOT MENTIONED IN THE ELECTRONIC OR PAPER CHKLIST WERE VERIFIED AS BEST AS POSSIBLE TO BE BENIGN. B) DID NOT RESOLVE THE PROB. MAINT CTL MENTIONED THAT PER THE MEL THE ACFT COULD NOT BE DISPATCHED OVER WATER IN SUCH A CONDITION. DISPATCH POINTED OUT THAT THIS CONDITION DISQUALIFIED US FOR ETOPS DISPATCH. AT THE TIME OF THIS EVAL WE HAD NOT YET ENTERED ETOPS AIRSPACE; AND NOT EVEN RECEIVED OR EVEN ACCEPTED OUR ETOPS WX BRIEFING AND DISPATCH. THE CREW WAS RELUCTANT TO PROCEED ON A 9+ HR FLT OVER THE NORTH PACIFIC WITH THE POSSIBILITY ONLY 1 PACK WAS OPERATING. IT WAS CONFIRMED BY MAINT CTL THAT THE PACK THAT HAD BEEN TURNED OFF PER THE CHKLIST WOULD NOT HAVE STANDBY CAPABILITY; AND THAT THE REMAINING OPERATING PACK WAS OPERATING AT MAX CAPABILITY PER THE TEMP READINGS. ACCORDINGLY THE DECISION WAS MADE TO RETURN TO SEATTLE. CLRNC TO RETURN TO SEA WAS RECEIVED FROM YVR CTR; FUEL WAS JETTISONED TO A LEVEL THAT WOULD ASSURE A LNDG UNDER MAX LNDG WT. IT WAS NOT NECESSARY TO DECLARE AN EMER. THE RETURN TO SEATTLE AND START OF JETTISON WAS INITIATED APPROX 250 MI W OF TOU. WE DSNDED TO FL310 PER YVR CTR CLRNC. THE DISTANCE REFLECTS THE CONSIDERABLE PERIOD CONTACTING DISPATCH; MAINT CTL AND THE EXTENSIVE ATTEMPT TO TROUBLESHOOT THE PROB SO THAT WE COULD SAFELY PROCEED TO NRT; THOUGH IN THIS EVENT IT WAS NOT POSSIBLE. FUEL AT START OF JETTISON WAS APPROX 152000 LBS. JETTISON WAS ENDED APPROX 30 MI W OF TOU AT APPROX 62000 LBS. THIS ALLOWED A LNDG WT UNDER MAX LNDG WT. FUEL AT LNDG WAS APPROX 57000 LBS FOR AN ACTUAL LNDG WT OF APPROX 457000 LBS; THE 3000 LBS 'OVERSHOOT' WAS DUE TO A LAG IN THE FMC CALCULATED LNDG WT WHILE JETTISONING W OF TOU.