Flight Crew Last 90 Days 210; Flight Crew Total 12200; Flight Crew Type 1300
Confusion
Aircraft Equipment Problem Critical; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Air Traffic Control Provided Assistance; Flight Crew Landed in Emergency Condition; Flight Crew Returned To Departure Airport; General Declared Emergency; General Maintenance Action
Aircraft; Human Factors; Procedure
We taxied out to Runway XXL in ZZZ without any incident.  Takeoff was normal with normal indications.  We weighed 170;000 LBS and had almost full tanks of gas with a full load of passengers heading to ZZZ1.  Shortly after takeoff the Captain asked if I smelled anything.  I replied; 'Yes.'  It was not the normal galley/food smell; high heat smell or electrical burning smell; but more of a burning oil smell.  I associated it with the possible factories that we fly over in the ZZZ area.  The Captain called the flight attendants to see if they smelled it and they also smelled it in the back of the cabin.  Once the Captain heard this; he said that we were going to return to ZZZ.  I put my mask on and established communication (comm) and the Captain did as well.  ATC asked if we were declaring an emergency and the Captain responded; 'Yes.'  The Captain ran the checklist and I put the autopilot on and began the decent back to ZZZ for a landing on XXL.  We were only about 20 miles from the airport when we began the return.  My thought process was to get the aircraft on the ground as soon as possible and the Captain seemed to be the same. He ran as quickly as possible through the Smoke/Odor/Fumes Checklist while I set up for a 40-Flap max brakes; overweight landing.  We came back together on Final and ran through the Approach/Descent; Approach Checklist and set up to land.  After landing we called the flight attendants to see if they saw or smelled any more odors.  They did not and we proceeded to the gate.  Maintenance met us at the gate and said that they had borescoped the engine the night prior.  They said that nine out of ten times that is the cause of the smell.
Reporter stated he only smelled an odor; did not see any smoke; same for the flight attendants in the forward and aft cabin. He was not familiar with the engine borescope procedures that Maintenance performed other than Maintenance opened the borescope plugs and inspected the CFM-56 Engine.
Shortly after takeoff; I noticed a smell of electrical smoke in the cockpit.  As we climbed through 3;000; I felt the Circuit Breaker (CB) panels for heat.  I then called the flight attendants (F/A) to ask if they were using the ovens.  They replied; 'No.'  They also smelled smoke in both forward and aft sections of cabin.  First Officer (F/O) and I had a short discussion on what could be the cause. I chose to declare an emergency; and return to ZZZ; as I could not readily locate the source of the smoke. ATC cleared us to level off at 10;000. I instructed the F/O to continue flying.  He called for the Smoke Checklist. We were given vectors to ZZZ; I was also trying to communicate with the F/As about returning to ZZZ. I told them 5 minutes; but I did not tell them about the possibility that we may need to evacuate the airplane after landing. I had trouble locating the correct checklist the Pilot Flying called for. I was looking in wrong sections.  Pilot Flying donned mask. I had trouble communicating with him. I donned my mask and goggles about a minute or two after he did; we established communications. I found the Checklist; and ran it through the first two pages.  I stopped there to make sure we were ready for landing as we were now on final for XXL.  Approach Descent; Approach and Landing Checklist accomplished. Flap 40; Auto Brake max landing; approximately 170;000 lbs. F/O made a smooth touch down. We exited at Taxiway Mike.  The smell had dissipated significantly by then; I elected not to evacuate and taxied to [the gate].  Pilot Flying made some ATC calls and adjusted altitude selector as I was busy with other tasks.  F/O handled the workload I gave him with ease. Crew Coordination. Checklist confusion.
A Captain and First Officer report about a burning oil smell in the flight deck and cabin of a NexGen B737 aircraft shortly after takeoff. An emergency was declared and an air turnback accomplished. Maintenance noted that a Borescope Inspection had been accomplished on the CFM-56 engines the night before.