Narrative:

Flight had a normal departure. Shortly after leveling off; west of tou at initial assigned altitude of FL320 we received an EICAS message 'pack left?' we followed the electronic checklist; which indicated a left pack overheat and left pack shutdown. The checklist ended by requiring the left pack to be turned off. We initiated a call to dispatch and had them patch us through to maintenance control. Maintenance control led us through some troubleshooting routines that a) while they were not mentioned in the electronic or paper checklist were verified as best as possible to be benign. B) did not resolve the problem. Maintenance control mentioned that per the MEL the aircraft 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 evaluate 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+ hour flight over the north pacific with the possibility only 1 pack was operating. It was confirmed by maintenance control that the pack that had been turned off per the checklist would not have standby capability; and that the remaining operating pack was operating at maximum capability per the temperature readings. Accordingly the decision was made to return to seattle. Clearance to return to sea was received from yvr center; fuel was jettisoned to a level that would assure a landing under maximum landing weight. It was not necessary to declare an emergency. The return to seattle and start of jettison was initiated approximately 250 mi west of tou. We descended to FL310 per yvr center clearance. The distance reflects the considerable period contacting dispatch; maintenance control and the extensive attempt to troubleshoot the problem so that we could safely proceed to nrt; though in this event it was not possible. Fuel at start of jettison was approximately 152000 pounds. Jettison was ended approximately 30 mi west of tou at approximately 62000 pounds. This allowed a landing weight under maximum landing weight. Fuel at landing was approximately 57000 pounds for an actual landing weight of approximately 457000 pounds; the 3000 pounds 'overshoot' was due to a lag in the FMC calculated landing weight while jettisoning west of tou.

Related reports:

Google
 

Original NASA ASRS Text

Title: 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.

Data retrieved from NASA's ASRS site as of January 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.