Narrative:

Flight XXX was scheduled to depart ZZZZ1 to iad on sunday. The flight crew consisted of captain X, first officer X and first officer Y, we arrived at the airport approximately 1 and ? Hours prior to departure. Preflight and departure briefing was normal. On taxi out we noted a pack mode left EICAS message after engine start. We taxied to a hardstand, so maintenance could work the problem. Dispatch and maintenance control were called several times. After approximately 4 hours we determined we could continue with the left pac deferred. A new release was obtained with the deferral. Taxi, takeoff and climb to initial cruise altitude were uneventful. It was warmer in the cockpit than normal on climb out since the left pack was operating in the standby mode initially. By the time we reached fl 320 the left pack was operating in the normal mode and the cockpit was cooling down. The flight was uneventful for the first 1 and ? Hours. 30 mins after takeoff first officer left the cockpit for first break and I occupied the right seat. We were about 100 NM northwest of ZZZZ when we got a call from the cabin that there was heavy smoke in the cabin. Captain X asked if they could see flames and they said no. They said the smoke was getting heavier. We got many more dings over the cabin interphone. I think there was a flight attendant at every station all trying to call the cockpit at the same time to report the smoke. Captain X said we needed to land immediately and I agreed. We immediately declared an emergency with ATC and squawked 7700. Captain X took control of the aircraft and called for emergency descent. I accomplished the checklist including the reference items. We determined that ZZZ was the nearest suitable alternate and ZZZZ radar provided vectors toward the field. The alternate page on the FMC was selected and egla was executed. During the descent we noticed a pack mode right EICAS message at approximately 10000 ft. We started dumping fuel and notified ATC. Initially we were planning for a straight in to runway 05. ATC advised us that the winds at 3000 ft would be a 30 KT tailwind, so we decided to land on runway 23. We turned off the gasper and recirc fans upper and lower. The approach was briefed and all normal checklists were accomplished. We were advised by ATC to stop dumping fuel at 9 NM final which we did. We were approximately 488000 pounds for landing which is 28000 pounds overweight. Autobrakes 4 was used and a smooth landing was executed by captain X. Callback conversation with reporter revealed the following information: the reporter stated the cause of the smoke in the center passenger cabin was caused by the left pack air cycle machine seizing. The reporter said the airplane landed overweight with no damage. Callback from acn 598911: the reporter stated the cause of the smoke in the passenger cabin is unknown as maintenance has released no details on the component failure.

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Original NASA ASRS Text

Title: A B777 IN CRUISE AT FL330 DECLARED AN EMER AND DIVERTED DUE TO SMOKE IN THE CENTER PAX CABIN. CAUSED BY LEFT PACK AIR CYCLE MACHINE FAILURE.

Narrative: FLT XXX WAS SCHEDULED TO DEPART ZZZZ1 TO IAD ON SUNDAY. THE FLT CREW CONSISTED OF CAPT X, FO X AND FO Y, WE ARRIVED AT THE ARPT APPROX 1 AND ? HRS PRIOR TO DEP. PREFLT AND DEP BRIEFING WAS NORMAL. ON TAXI OUT WE NOTED A PACK MODE L EICAS MSG AFTER ENG START. WE TAXIED TO A HARDSTAND, SO MAINT COULD WORK THE PROB. DISPATCH AND MAINT CTL WERE CALLED SEVERAL TIMES. AFTER APPROX 4 HRS WE DETERMINED WE COULD CONTINUE WITH THE LEFT PAC DEFERRED. A NEW RELEASE WAS OBTAINED WITH THE DEFERRAL. TAXI, TKOF AND CLB TO INITIAL CRUISE ALT WERE UNEVENTFUL. IT WAS WARMER IN THE COCKPIT THAN NORMAL ON CLBOUT SINCE THE L PACK WAS OPERATING IN THE STANDBY MODE INITIALLY. BY THE TIME WE REACHED FL 320 THE L PACK WAS OPERATING IN THE NORMAL MODE AND THE COCKPIT WAS COOLING DOWN. THE FLT WAS UNEVENTFUL FOR THE FIRST 1 AND ? HRS. 30 MINS AFTER TKOF FO LEFT THE COCKPIT FOR FIRST BREAK AND I OCCUPIED THE RIGHT SEAT. WE WERE ABOUT 100 NM NW OF ZZZZ WHEN WE GOT A CALL FROM THE CABIN THAT THERE WAS HEAVY SMOKE IN THE CABIN. CAPT X ASKED IF THEY COULD SEE FLAMES AND THEY SAID NO. THEY SAID THE SMOKE WAS GETTING HEAVIER. WE GOT MANY MORE DINGS OVER THE CABIN INTERPHONE. I THINK THERE WAS A FA AT EVERY STATION ALL TRYING TO CALL THE COCKPIT AT THE SAME TIME TO RPT THE SMOKE. CAPT X SAID WE NEEDED TO LAND IMMEDIATELY AND I AGREED. WE IMMEDIATELY DECLARED AN EMER WITH ATC AND SQUAWKED 7700. CAPT X TOOK CTL OF THE ACFT AND CALLED FOR EMER DSCNT. I ACCOMPLISHED THE CHKLIST INCLUDING THE REFERENCE ITEMS. WE DETERMINED THAT ZZZ WAS THE NEAREST SUITABLE ALTERNATE AND ZZZZ RADAR PROVIDED VECTORS TOWARD THE FIELD. THE ALTERNATE PAGE ON THE FMC WAS SELECTED AND EGLA WAS EXECUTED. DURING THE DSCNT WE NOTICED A PACK MODE R EICAS MSG AT APPROX 10000 FT. WE STARTED DUMPING FUEL AND NOTIFIED ATC. INITIALLY WE WERE PLANNING FOR A STRAIGHT IN TO RWY 05. ATC ADVISED US THAT THE WINDS AT 3000 FT WOULD BE A 30 KT TAILWIND, SO WE DECIDED TO LAND ON RWY 23. WE TURNED OFF THE GASPER AND RECIRC FANS UPPER AND LOWER. THE APCH WAS BRIEFED AND ALL NORMAL CHKLISTS WERE ACCOMPLISHED. WE WERE ADVISED BY ATC TO STOP DUMPING FUEL AT 9 NM FINAL WHICH WE DID. WE WERE APPROX 488000 LBS FOR LNDG WHICH IS 28000 LBS OVERWT. AUTOBRAKES 4 WAS USED AND A SMOOTH LNDG WAS EXECUTED BY CAPT X. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE CAUSE OF THE SMOKE IN THE CENTER PAX CABIN WAS CAUSED BY THE L PACK AIR CYCLE MACHINE SEIZING. THE RPTR SAID THE AIRPLANE LANDED OVERWT WITH NO DAMAGE. CALLBACK FROM ACN 598911: THE RPTR STATED THE CAUSE OF THE SMOKE IN THE PAX CABIN IS UNKNOWN AS MAINT HAS RELEASED NO DETAILS ON THE COMPONENT FAILURE.

Data retrieved from NASA's ASRS site as of July 2007 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.