Air Carrier Flight Crew reported a Flight Attendant notification of a 'strong burning' odor in the cabin during initial climb. Flight crew returned to the departure airport where a safe landing was completed.
Synopsis
Air Carrier Flight Crew reported a Flight Attendant notification of a 'strong burning' odor in the cabin during initial climb. Flight crew returned to the departure airport where a safe landing was completed.
Narrative
During the climb out of ZZZ we were passing through about 7;000 ft. The bleed configuration was still the same from takeoff: engine bleeds on; APU bleed off; packs auto; isolation valve auto; recirc fans on; trim air on. Around this time we entered icing conditions and turned the engine anti-ice on. Moments later we received a call from the cabin. They reported a 'strong burning' smell; no visible smoke; and it was not obvious where it was coming from. While the First Officer (FO) and I began to diagnose the situation we received another call from the cabin indicating that odor was getting worse. The FO and I put our oxygen masks on; [requested priority handling] to return to ZZZ. Throughout the event the Flight Attendants (FA) reported difficulty breathing; dizziness; and one of them developed a nose bleed. We ran the non-normal checklist. The Flight Attendants reported that odor/fumes had improved in the back of the aircraft and the forward Flight Attendant stated it was no longer getting worse. The approach and landing was normal. Airport Rescue and Firefighting (ARFF) did a thermal scan of the aircraft after we cleared the runway. Everything on the exterior of the aircraft appeared normal. We taxied to the terminal and deplaned normally. The Flight Attendants reported that none of the passengers had requested medical assistance. The number 4 Flight Attendant with the nose bleed reported they were in stable condition to complete the deplaning process and was treated for the condition afterwards.Communicating with the oxygen masks on is very loud and adds a distraction and barrier to communication. Task saturation was a challenge as well. Reinforcing the importance of following SOPs and using good threat and error management will help crews navigate events like these with a successful outcome.
Second reporter narrative
During initial climb; Flight Attendants called to report an odor in the cabin. Captain and I donned our oxygen masks; [requested priority handling to departure airport]; completed the appropriate checklists and returned to ZZZ without further incident.The only suggestion that I have is to train pilots exactly how to communicate with the oxygen mask on.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.