Narrative:

On taxi out we had a strong odor that was reminiscent of chicken cooking. Thought it was possibly from chicken sandwich flying first officer had brought on board, as did the relief first officer. When odor did not dissipate after a time, it was presumed to be from the galley(south), so we queried the galley, and they said they had nothing cooking at the time. The odor was strong, but we did not associate it with a known malfunction, and I presumed it would pass. Upon takeoff, the odor appeared to dissipate very quickly. Soon thereafter, however, we started receiving numerous calls from the flight attendants indicating a strong, acrid, burning smell in the cabin, and throughout the mid to aft cabin area. The relief first officer inquired as to specifics, and we waited a brief period to see if it would dissipate. It did not, and we received a number of confusing calls from the cabin, haze, smoke from a lavatory waste bin, a waste bin fire extinguisher discharge. Most of these calls proved later to be either unfounded, or unverifiable, though there was a consensus regarding the odor in the cabin, and the flight attendant at door 3R insisted the saw a smoky haze in the cabin. As the calls were numerous, and could not be specifically located, I decided I had to consider the possibility of an unknown, undetermined fire, and opted to return to ZZZ. We did not prepare the cabin as things were quite hectic, but declared an emergency and returned to ZZZ. We were delayed in our return due to miscoms due to wrongly assigned frequencys, but once initiated, return was expeditious. Landing runway 14R, we were met and escorted by emergency equipment to the gate after an exterior inspection by rescue personnel for signs of smoke or fire, none of which was found. An interior of the aircraft revealed no fire or problem source. The nearest thing to probable cause was a maintenance person suggesting oil or grease in the pack system, though this was not verified by the time we departed the aircraft.

Related reports:

Google
 

Original NASA ASRS Text

Title: A B777-200 FLT ATTENDANT CREW DEPARTING ORD NOTICED STRONG BURNING SMELL IN CABIN. FLT CREW DECLARED AN EMER AND RETURNED TO ORD.

Narrative: ON TAXI OUT WE HAD A STRONG ODOR THAT WAS REMINISCENT OF CHICKEN COOKING. THOUGHT IT WAS POSSIBLY FROM CHICKEN SANDWICH FLYING FO HAD BROUGHT ON BOARD, AS DID THE RELIEF FO. WHEN ODOR DID NOT DISSIPATE AFTER A TIME, IT WAS PRESUMED TO BE FROM THE GALLEY(S), SO WE QUERIED THE GALLEY, AND THEY SAID THEY HAD NOTHING COOKING AT THE TIME. THE ODOR WAS STRONG, BUT WE DID NOT ASSOCIATE IT WITH A KNOWN MALFUNCTION, AND I PRESUMED IT WOULD PASS. UPON TKOF, THE ODOR APPEARED TO DISSIPATE VERY QUICKLY. SOON THEREAFTER, HOWEVER, WE STARTED RECEIVING NUMEROUS CALLS FROM THE FLT ATTENDANTS INDICATING A STRONG, ACRID, BURNING SMELL IN THE CABIN, AND THROUGHOUT THE MID TO AFT CABIN AREA. THE RELIEF FO INQUIRED AS TO SPECIFICS, AND WE WAITED A BRIEF PERIOD TO SEE IF IT WOULD DISSIPATE. IT DID NOT, AND WE RECEIVED A NUMBER OF CONFUSING CALLS FROM THE CABIN, HAZE, SMOKE FROM A LAVATORY WASTE BIN, A WASTE BIN FIRE EXTINGUISHER DISCHARGE. MOST OF THESE CALLS PROVED LATER TO BE EITHER UNFOUNDED, OR UNVERIFIABLE, THOUGH THERE WAS A CONSENSUS REGARDING THE ODOR IN THE CABIN, AND THE FLT ATTENDANT AT DOOR 3R INSISTED THE SAW A SMOKY HAZE IN THE CABIN. AS THE CALLS WERE NUMEROUS, AND COULD NOT BE SPECIFICALLY LOCATED, I DECIDED I HAD TO CONSIDER THE POSSIBILITY OF AN UNKNOWN, UNDETERMINED FIRE, AND OPTED TO RETURN TO ZZZ. WE DID NOT PREPARE THE CABIN AS THINGS WERE QUITE HECTIC, BUT DECLARED AN EMER AND RETURNED TO ZZZ. WE WERE DELAYED IN OUR RETURN DUE TO MISCOMS DUE TO WRONGLY ASSIGNED FREQS, BUT ONCE INITIATED, RETURN WAS EXPEDITIOUS. LNDG RWY 14R, WE WERE MET AND ESCORTED BY EMER EQUIP TO THE GATE AFTER AN EXTERIOR INSPECTION BY RESCUE PERSONNEL FOR SIGNS OF SMOKE OR FIRE, NONE OF WHICH WAS FOUND. AN INTERIOR OF THE ACFT REVEALED NO FIRE OR PROB SOURCE. THE NEAREST THING TO PROBABLE CAUSE WAS A MAINT PERSON SUGGESTING OIL OR GREASE IN THE PACK SYS, THOUGH THIS WAS NOT VERIFIED BY THE TIME WE DEPARTED THE ACFT.

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.