Date: 201909
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Light: Daylight
Aircraft: B737-800
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Climb
Airspace: Class B ZZZ
ATC / advisory: Tower ZZZ
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Human factors: Situational Awareness; Workload; Time Pressure
Second reporter function: First Officer; Pilot Not Flying
Anomaly: Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Weight And Balance; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Detector: Person Flight Attendant; Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew Landed in Emergency Condition; Flight Crew Overcame Equipment Problem; Flight Crew Returned To Departure Airport
Contributing factors: Aircraft; Human Factors
Primary problem: Aircraft

Narrative: During climb off of ZZZ on the ZZZZZ6 RNAV SID; at 1;000 feet AGL; just as we were beginning the normal cleanup routine; the flight attendants chimed us with the 4-chime call. I immediately realized that I could smell 'something' and the flight attendants described the same observation. I immediately directed my First Officer to don O2 masks. It was a flaps-15 takeoff; so we continued the cleanup process while I hand flew the aircraft while donning my oxygen mask. We continued to fly the SID to the 4;000 hold-down; while notifying ATC of our [situation] and request for vectors for an immediate return.The remainder of the flight was uneventful. We launched off Runway 15R and recovered via a 'figure-8' left turn to downwind for the RNAV Runway 10. I touched down very gently; with the power up; because I knew that this would affect the overweight landing inspection procedure. I was easy on the brakes. The aircraft decelerated well in maximum reverse. Fire trucks followed us onto the runway and surrounded the aircraft. They looked the aircraft over and used an IR camera to examine the aircraft. After declaring no unusual observations; they then followed us to the gate.Once we donned oxygen masks; we were committed to making an expeditious recovery. Although we did not know the source or origin of the detected odors; we 'assumed the worst' and I was personally convinced that it was necessary to return as soon as possible. (I was later informed by Maintenance Control that they found a failed static inverter.)My First Officer; who is very experienced and ready for upgrade; was a great partner to fly with during this [situation]. He was eager to divide responsibilities. He flew the aircraft and talked with ATC as I read the QRC then QRH. Knowing the systems and the likelihood of the air conditioning packs as a source of trouble; I directed the First Officer to secure both packs. As we worked through the QRH; the checklist confirmed that shutting off the packs was going to be part of the troubleshooting process.We made one error which I would like to highlight for the purpose of enlightening other Crews to be on the lookout for repeating this same error: We were given quick vectors to recover to landing in a short time. This left us short on time to 'properly' prepare for landing in an orderly fashion.Adding to this self-imposed sense of urgency was the fact that we were wearing oxygen masks. The desire to 'end' the evolution with a sense of urgency led us to accept a prompt set of vectors to land. Since it was a 'Smoke; Fire; Fumes' Checklist; there is an ever-present sense of urgency and desire to get back on deck as soon as possible. This is my 'General Safety' concern.Specifically; while slowing and configuring for landing on final; approaching 150 knots; we realized that we had failed to set VREF and VARGET. This reminded us that we had not retrieved landing data via ACARS; as we would 'normally' do. My First Officer quickly selected the FMC default values; which I judged to be satisfactory; especially as we knew that we were intentionally performing an overweight landing owing to the nature of the [situation].In hindsight; I allowed the aircraft to slow without a solid plan and without having communicated a set plan for the approach. This 'speed error' was trapped; but we could have easily gotten slower; given all of the distractions. We also failed to use [weight and balance system] to gather requisite landing data. This is a procedural error; which we accepted owing to task prioritization.Needless to say; using oxygen masks is a huge and primary distraction. It makes communication of all sorts very problematic. It impedes and precludes 'normal' conversational speech to which we are accustomed. This is my first; ever experience in the 737 flying an approach and landing while wearing an oxygen mask.I think that we failed to 'assess the risk' associated with not running a normal Descent-Approach-Landing Checklist sequence. Also; because of the difficulties in communication while using oxygen masks; we restrained ourselves from speaking; excessively (or 'normally').I want to add that once we were established and had found our rhythm of breathing; then keying the MIC to speak; we felt very comfortable and confident. We both felt like we were completely unimpeded by the oxygen masks - i.e. no problems with vision obstruction or clarity nor mobility in the cockpit. It was almost like we weren't wearing them; except for the fact that we wanted to speak as little as possible!Simply put; the oxygen mask usage causes simultaneous failures to communicate; the loop is left open and the sender does not know if the receiver even heard what was said or if it was heard correctly. Once using oxygen masks; one must very deliberately repeat; interrogate and confirm that messages have been received; understood and acted upon. It takes deliberate follow-through and demands excessive communication at a time when both pilots are seeking to minimize conversation and distracting sounds/noises.


Second narrative: While climbing out of ZZZ; we stopped our climb at 4;000 [feet] and reported to ZZZ Departure that we had unusual fumes in the cockpit and cabin. Moments earlier the flight attendants at both stations had chimed us to tell us about the fumes; which were apparent in the cabin. We donned our oxygen masks; and completed the QRC Checklist. The PIC handed control of the aircraft and radios to me and continued to work the problem and the QRH. The PIC communicated with the flight attendants and the passengers. I handled the aircraft and communicated with ZZZ Departure to coordinate our return to ZZZ. We [advised ATC] and returned to ZZZ on Runway 10 approximately 15 minutes after our initial departure. The aircraft was stopped on Runway 10 while ARFF Crews examined the exterior and the Captain made sure everything was fine in the cabin. We then taxied to our gate where the passengers were deplaned; and arrangements made to continue to ZZZ1.We all worked well as a group; there was great communication between the flight attendants; pilots and passengers. ATC and ARFF handled our [situation] with professionalism. Only a few minor things could have gone better. One example of this was the Diversion Checklist. Most of the items were completed; but not because we read the checklist itself. It may have gone even smoother if we had gone to the Diversion Checklist after the QRH. Maybe a note at the end of the QRH Checklist to do the Diversion Checklist could help. Another minor item was talking with Dispatch. We sent a quick ACARS to Dispatch but didn't have a chance to ACARS back or call them until we landed at ZZZ. Dispatch did send performance numbers for weight and balance as well as landing performance via ACARS.Given that the SMOKE; FIRE or FUMES Checklist is long and somewhat difficult to get through; we completed it in a timely manner and returned to ZZZ safely.We used our oxygen mask for the whole event; communication proved to be easier than we expected; and we didn't feel it prevented us from having any further difficulties getting the aircraft back to ZZZ.


Synopsis: B737-800 flight crew reported a fumes event shortly after takeoff resulting a return to departure airport.