Date: 202003
Flight conditions: VMC
Aircraft: B737 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Climb
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: First Officer; Pilot Flying
Anomaly: Aircraft Equipment Problem Less Severe; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Detector: Person Flight Crew; Person Flight Attendant
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew Returned To Departure Airport; Flight Crew Landed in Emergency Condition; Flight Crew Overcame Equipment Problem; Flight Crew Requested ATC Assistance / Clarification; General Maintenance Action
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: During climb; First Officer and I noticed and discussed a strong burning smell wondering if something was burning in one of the ovens. Right after that Flight Attendant called to report a strong burning smell. I asked if anything was in the ovens and she replied no and she would investigate and call back. Shortly she called and said the smell could not be identified but appeared to be coming from the air ducts. First Officer and I discussed it briefly and I advised her we would return for landing with 10 minutes remaining in flight and a normal landing. First Officer continued as flying pilot with autopilot engaged and managed programming the FMC for a return to ZZZ. I ran the smoke fire fumes checklist; used ACARS for sending the divert message; and continued communication with ATC including [requesting priority handling]. While running the checklist we decided the oxygen masks were not needed. Then we completed the normal checklists. I made a brief PA to the passengers. We noticed the off-schedule descent light and noted we were returning to the departure field taking no further action on that light with consideration of being on approach. I asked if First Officer was good to continue as flying pilot through the landing and he completed a nice landing.


Second narrative: On climbout from ZZZ; I noticed a burning smell. I confirmed with Captain that he smelled something awry; a bit less acrid that an electrical fire smell; but definitely not a smell associated with normal operations. We both wondered aloud if perhaps the flight attendants had left something in the oven and perhaps it was burning. I was the Pilot Flying and about this time the Purser called and Captain spoke with her. I could overhear that Captain was discussing the smell with the Purser. He passed along that both the flight attendants and the passengers could smell something burning as well. Captain asked the purser to have a look at the galley areas and the lavatories. The Purser reported back that they could not find anything burning but nevertheless still smelled the odor. During this time Captain and I discussed returning to ZZZ. To me; the odor was gone/dissipated; but we agreed that an air return was the best option. I remained the Pilot Flying while Captain did the initial coordination with ATC. He described the situation to ATC and I started on vectors to return to ZZZ for the ILS. ATC then queried whether we were going to [request priority handling] and Captain replied in the affirmative. I continued with autopilot as we were vectored for the approach. I reprogrammed the FMC for the approach while Captain ran the smoke/fume/fire checklist. At this point we had considered donning masks/regulators but I believed that in the time-compressed environment on short approach that masks/regulators presented a threat of distraction and loss of situational awareness. We mitigated the threat by leaving the masks stowed with no visible indication of smoke/fire and with the fumes dissipated on the flight deck. The ACARS diversion option populated at I programmed the ARR and queried Captain if he had notified Dispatch yet. Sure enough; he already had. I then verified the NAVAIDS/COURSE/MINS and quickly briefed the approach as we were on dogleg to final. Captain made a PA announcement to the passengers to assuage any concerns about firetrucks/first responders on rollout. We then discussed clearing the runway after landing which we both agreed was the best course of action. We got the 'off scheduled descent' light but pressed without performing that checklist due to our position on the approach; noting that we were returning to our departure field. We were pushed to the single frequency approach frequency and I remained the pilot flying and configured around 10-12 DME. Captain ran the landing checklist and we landed uneventfully; transferred aircraft control with idle reverse and cleared the runway. After getting the 'all safe' from the Fire Chief; we returned to the gate; ran the appropriate checklists and Captain made another PA announcement to the passengers. First responders boarded; inspected and gave us the 'all clear' to deplane.


Synopsis: B737 flight crew reported that a fumes event during climb resulted in a return to the departure airport.