Narrative:

On the climb out of ZZZZ the flight attendant's called and said there was a burning smell in the back of the AC. They also reported seeing smoke. The captain asked the other international relief officer to go back and assess the situation. Approximately 5 minutes later he calls the flight deck and said there was a burning smell but he suspected it was an oven and was not concerned. The captain asked me to go back and see what I thought. When I got to the back of the jet I could smell a burning smell as well. I did not see any smoke but the flight attendant's said they did and used the [urgent] words with me. They were concerned; did not feel safe and wanted to return. I called the captain on the interphone and told him what I had observed; smelled as well as what the flight attendant's had voiced to me as far as their concern. He said we would troubleshoot and continue on. When I told the flight attendant's this they were not happy and started calling the captain and again telling him they were concerned; did not feel safe; and wanted to return. He told them the same thing that he told me.when I returned to the flight deck I asked the captain what he thought about returning to ZZZZ. He told me he could 'find nothing wrong with his airplane.' at this point I was not comfortable continuing on a 13 hour ETOPS flight with an unknown burning smell in the back of the airplane. The decision was then made to contact maintenance control and get their opinion on the next course of action. They suspected what we did that it could be a galley oven malfunction but could not be 100% sure that was the problem. They agreed that the safest course of action would be to return. At this point the decision was made to return. Next; we began the diversion process and ran all appropriate checklists and followed all diversion procedures. We were going to land overweight so we had to also jettison approximately 100;000 lbs of fuel. We had a problem with the auto fuel balance system and ran the appropriate checklist for that as well. We ended up making it back safely with no injuries or substantial damage to the airplane. The mechanics suspected it was a heating element malfunction in the aft galley oven but had not concluded that with 100% certainty when we left the airplane and headed back to our hotel.

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Original NASA ASRS Text

Title: B787 First Officers were informed by the cabin crew that there was smoke and fumes in the aft galley apparently from a failed oven. The oven was switched off and the circuit breaker was pulled; but the flight attendants wanted to return to the departure airport. However; the Captain believed the problem was solved. Maintenance Control was contacted and after some deliberation the flight returned to the departure airport.

Narrative: On the climb out of ZZZZ the FA's called and said there was a burning smell in the back of the AC. They also reported seeing smoke. The Captain asked the other IRO to go back and assess the situation. Approximately 5 minutes later he calls the flight deck and said there was a burning smell but he suspected it was an oven and was not concerned. The captain asked me to go back and see what I thought. When I got to the back of the jet I could smell a burning smell as well. I did not see any smoke but the FA's said they did and used the [urgent] words with me. They were concerned; did not feel safe and wanted to return. I called the captain on the interphone and told him what I had observed; smelled as well as what the FA's had voiced to me as far as their concern. He said we would troubleshoot and continue on. When I told the FA's this they were not happy and started calling the Captain and again telling him they were concerned; did not feel safe; and wanted to return. He told them the same thing that he told me.When I returned to the flight deck I asked the Captain what he thought about returning to ZZZZ. He told me he could 'find nothing wrong with his airplane.' At this point I was not comfortable continuing on a 13 hour ETOPS flight with an unknown burning smell in the back of the airplane. The decision was then made to contact Maintenance Control and get their opinion on the next course of action. They suspected what we did that it could be a galley oven malfunction but could not be 100% sure that was the problem. They agreed that the safest course of action would be to return. At this point the decision was made to return. Next; we began the diversion process and ran all appropriate checklists and followed all diversion procedures. We were going to land overweight so we had to also jettison approximately 100;000 lbs of fuel. We had a problem with the auto fuel balance system and ran the appropriate checklist for that as well. We ended up making it back safely with no injuries or substantial damage to the airplane. The mechanics suspected it was a heating element malfunction in the aft galley oven but had not concluded that with 100% certainty when we left the airplane and headed back to our hotel.

Data retrieved from NASA's ASRS site 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.