Date: 201910
Local time of day: 0601-1200
Location: ZLA.ARTCC, CA
Flight conditions: VMC
Aircraft: B757-200
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Landing; Cruise; Descent
Airspace: Class A ZLA; Class E ZLA
ATC / advisory: Center ZLA
Aircraft component: Galley Fire/Overheat Warning
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Second reporter function: Pilot Flying; First Officer
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Weight And Balance; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew Landed in Emergency Condition; Flight Crew Diverted; General Maintenance Action; General Flight Cancelled / Delayed
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: Upon leveling off at 37;000 feet 'Lavatory Smoke' displayed on the EICAS. As we got into the QRC/QRH; the caution light extinguished. We assumed it was a false indication at that point; however; approx 15 to 20 seconds later; another 'Lavatory Smoke' caution displayed followed by a cabin call from the aft galley station Flight Attendants. They explained to me that the smoke alarms in the lavatory were going off (I could also hear the alarms in the background) but that it was just from the ovens and that the smoke was already dissipating. The First Officer reminded me that one of the ovens had just been replaced so between that information and the Flight Attendant's suggestion that smoke was getting less we figured it was a temporary situation. The second 'Lavatory Smoke' illumination had also extinguished at that moment. I discussed with the Flight Attendants that we couldn't continue unless they were absolutely certain that the smoke was merely due to food in the oven and that that there indeed was no fire so I asked them to verify once more and get back to me. I also instructed them to cease use of the oven that was the source of the smoke. The First Officer was still 'pilot flying' so I told him to continue in that capacity while I finished the QRH. Right as I got to the section in the QRH that gave me the option; as the Captain; to continue (assuming smoke had properly dissipated and the source was removed); 'Lavatory Smoke' illuminated on the EICAS. At that moment the aft galley Flight Attendants called back and I could hear the lavatory smoke alarm in the background. As we discussed the source; I could hear the other Flight Attendant say; 'it started up again'... meaning the smoke started again. The Flight Attendant on the handset confirmed what she said and I then made the decision at that moment that the safest course of action would be to declare an emergency and divert to nearest airport. I informed the Flight Attendant on the handset to expect a further briefing from me but for now to plan on a diversion and to start preparing the cabin. At that point I turned to the First Officer and he agreed we needed to get on the ground. I informed ATC that we were declaring an emergency. The First Officer and I both agreed where  the safest and most logical airport to divert to was and we informed Center that we would like to divert. I then turned to the First Officer and said; 'You fly; I'll manage'. While he  began the descent and set the airplane up for the arrival; I asked him to oversee what I was doing to make sure I executed the QRH properly. Once I got the section in the QRH where it became a loop; I informed him. We both agreed that we can proceed no further in the QRH and I began my Captain duties with the Flight Attendant's and passenger announcements. I called the purser and informed her of the emergency in an official fashion; including use of the TEST acronym in detail to the plan; followed by an announcement to the passengers of our intentions to divert. I then got back with the First Officer and he briefed up the arrival and approach. As I completed the rest of the checklist and got caught up; I sent a message to dispatch on the ACARS that we were an emergency aircraft diverting due to persistent aft galley smoke.  We discussed that we would be overweight for landing by approximately 7;500 lbs. I felt since he was calibrated to the arrival and approach set up; and since I still needed to wrap up checklist adherence; he should complete the landing. I did inform ATC to have fire equipment standing by. Landing was uneventful. We taxied clear of the runway into a holding area and brought the aircraft to a stop. We then called the aft galley and verified that indeed all smoke has dissipated. We reported that to the fire ground crew and they informed us that they would follow us back to the gate out of an abundance of caution; which we of course appreciated. Upon arrival to the gate a crew of fire fighters boarded the aircraft to inspect the ovens and galley area and indeed declare the source of the smoke was eliminated. They reported to me that they felt it was a combination of residue in the ovens coupled with abnormally high amounts of steam. The maintenance staff then came aboard and ran the ovens for 12 minute cycles to confirm the same. They MEL'd the one oven that was putting out excess smoke and informed us that we could not use the other oven. I got on the PA in front of the passengers to explain what occurred and why it was important to take the safest course of action when it comes to smoke. I also informed them that we will do everything we can to get the flight back on track once our maintenance team completes their repairs and inspections and signs off the aircraft. Except for one passenger in First Class who snapped at me for the delay; everyone else was in good spirits and appreciative of our actions and efforts. We wrote up the aircraft for the ovens as well as for overweight landing. As we waited for the overweight landing inspection to get completed; First Officer and I discussed whether we would be fit to continue to our destination. We both agreed to get the aircraft ready for the next flight and reassess 10 minutes prior to push as our destination was on a 3 hour EDCT(Expect Departure Clearance Time) anyway. Operations was able to move the EDCT time up for us and upon 10 minutes prior to the actual push we assessed our state and both agreed that we were fit and in the right frame of mind to continue. I also contacted the FODM who was EXTREMELY supportive; professional; and helpful. She offered to get us anything we need; we just had to say the word. I informed her I would confer with my crew that they were all OK to continue (they all did an OUTSTANDING job) and that we would reassess 10 minutes prior to push and that I would call here and let her know either way. I then went to the aft galley to discuss the whole event with the Flight Attendants who were in the thick of the battle; as it were and thanked them for their professionalism and for being calm and collected. I was really impressed that my entire crew was so supportive and kept such a great attitude throughout. Not one complaint from anyone on my crew. The First Officer did an excellent job as well by flying to standards and backing up the captain 100%.


Second narrative: Aft galley oven producing persistent smoke. Smoke caused smoke alarm to sound and Lavatory Smoke EICAS warning. Cockpit called FA's to determine extent of smoke/fire. FA's said there was persistent smoke and steam coming from one or more ovens. Lavatory Smoke alarm went on and off 3 times over a 5 min period. Aft galley oven had recently been replaced. CA declared emergency. Crew diverted to LAS for an uneventful landing.


Synopsis: B-757 flight crew reported declaring an emergency and executing an uneventful emergency diversion due to smoke in the aft galley.