Air carrier flight crew reported a 'burning popcorn' scent during initial climb. After coordinating with Maintenance and Dispatch; the flight diverted to a suitable airport.
Synopsis
Air carrier flight crew reported a 'burning popcorn' scent during initial climb. After coordinating with Maintenance and Dispatch; the flight diverted to a suitable airport.
Narrative
Shortly after departure out of ZZZ and just prior to 10;000ft ALT; the first flight attendant called to inform us that the FA by the 3R door smelled a burning popcorn" scent around their area. This smell then moved to rows 11-27 and stayed in that area for the remainder of the event. There was no smoke and all systems up front were reporting normal; including all temperatures in the green zones. The smell was not dissipating and remained constant in rows 11-27. The next call was to dispatch through the satellite phone. We continued climbing up to our cruising altitude of FL330. I relayed the information from our first FA to dispatch and also received updates from the flight attendants on the event. Dispatch then connected Maintenance Control and I updated them on the situation. Updates were received from the FA that the smell wasn't dissipating and felt like a "burning of nostrils sensation/chemical." Suggestions from Maintenance Control were to check the lavs for possible pax smoking or through the aisles for possible burning. All were checked by the FA's and there was nothing out of the normal. With the information provided from all parties; I made the decision to start the process on an air turn back. This was due to the fact that our flight had just departed; had a remaining five hours en route over water; and the smell was not dissipating. ZZZ or ZZZ1 were my two choices for return and dispatch coordinated and confirmed a return to ZZZ1 was the best course for maintenance and plane replacement. After hanging up with dispatch we coordinated a clearance to ZZZ1 with ATC; with vectors to start. I made a passenger announcement informing them of a maintenance issue that we were experiencing and stated that out of an abundance of safety and with safety as our top priority; this needed to be resolved on the ground in ZZZ1. The FO and I then had time to set up for a return to ZZZ1. We requested weather and landing data. At this point the QRH overweight landing procedure was run through and I turned on the APU with plans to switch the APU bleed on at 10;000ft; per the procedure. Next; I placed another satellite call to dispatch giving ETA and requesting a re-release and notams for our ATB (Air Turn Back) to ZZZ1. Those came through our printer shortly after hanging up. I called back to the FA to ask if there were any changes with the smell; to provide time of arrival; gate; and plan of action for crew after getting into the gate. The smell was still present and now two of our FA's were experiencing headaches and possible light headedness. Clearance with ATC was initially vectors; then direct ZZZ2 for the ZZZZZ Arrival landing XXL. Because we were overweight I asked for negative LAHSO XXL and long approach due to higher VLS (Lowest Selectable Speed); because of the overweight scenario. At 10k we turned on the APU bleed; per the QRH overweight landing procedure; and read over the procedure again. Set up was Flaps full and no additive to our approach speed. All checklists were completed and a normal landing into ZZZ1 was performed. Landing weight was 179.4k and sink rate was 10 feet per min at touchdown. Taxi into gate 1 and after flight duties were then completed in the logbook and the fume event paper work was completed. I suggested the flight attendants be seen to be on the safe side and all cabin crew members were evaluated by medical ground personnel as well. Three write ups were added to the logbook: Fume event; ATB (Air Turn Back); and Overweight Landing."
Second reporter narrative
Operating flight from ZZZ to ZZZ2 during the climb out prior to 10;000 we received a call from the FA that the FA by door 3R was starting to smell what she said smelt like electrical burning". Upon further questioning she said it smelt like "burning popcorn". The FA said the smell was permeating from rows 11-27. We asked if there was smoke and she said no. We informed her to call us back if things got worse. At this point we pulled out our QRH and opened and reviewed the smoke/fumes procedure while calling up dispatch/mx on SATCOM. The FA's checked the lav for possible pax smoking and aisles for burning in which we heard they did not find any evidence of this. While talking to Mx/dispatch we called the FA back to see if the situation has got worse. The FA informed us the situation has not got any worse nor better. She said the best way to describe the smell was "a burn on your nostrils when you inhale and very chemically". At this point we have approx 5 hours to go oceanic with a smell that is "burning the nostrils while inhaling" the captain made the decision to turn back to ZZZ and I agreed. We had just leveled off at our cruising altitude of FL330 and now needed to pick an appropriate alternate airport. ZZZ and ZZZ1 we thought would be the best alternates to choose from; with coordination from dispatch we decided ZZZ1 would be the best alternate for a few reasons. 1 being the aircraft was overweight and the runway is longer at ZZZ1 and 2 the passengers could deplane and have an aircraft replacement so they can still fly to ZZZ2. After the decision to return to ZZZ1 the captain made a PA and we requested vectors from ATC. We informed them we would be unable for LAHSO operations. We reviewed the QRH overweight procedure and turned the APU on with plans to turn the APU bleed on going through 10;000ft. We received a dispatch re release and NOTAMS for our return to ZZZ1. Upon updating our FA's of our plan the smell was still present and they complained of being lightheaded with headaches. We were cleared to ZZZ1 via direct ZZZ3 for the ZZZZZ arrival. We turned the APU bleed on through 10;000; completed all checklists; reviewed the overweight procedure and the landing was very smooth and uneventful. We landed at gross weight 179.4k. Upon reaching gate medical met us on the plane to evaluate the cabin crew members and the captain made Mx logbook entries."
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.