Date: 202112
Local time of day: 0601-1200
Location: ZZZ.ARTCC, US
Flight conditions: VMC
Light: Daylight
Aircraft: B737 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Mission: Passenger
Flight phase: Climb
Aircraft component: Powerplant Fire/Overheat Warning
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Human factors: Workload; Time Pressure; Communication Breakdown; Situational Awareness
Second reporter function: Captain
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter Other / Unknown
Detector: Automation Aircraft Other Automation; Person Flight Crew
When detected: In-flight
Result: Flight Crew Inflight Shutdown; Flight Crew Returned To Departure Airport; Flight Crew Landed in Emergency Condition
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: It was day 4 of a 4-day trip. Crew rest was good; and I reported fit for duty about an hour before pick-up time from the hotel. We arrived at the plane slightly ahead of schedule. The Captain (CA) and I discussed a hydraulic leak on the aircraft that occurred the previous day. I was the first one on the plane and began the preflight. While testing the fire system I noticed the left engine fire loop did not illuminate. Further troubleshooting revealed the problem was with the 'B' loop. The CA reported the problem to maintenance. They confirmed the problem and deferred the issue. We left the system on the 'A' loop.  On the walk around I noticed that the left wheel well was abnormally dirty and still wet from the previous leak. I specifically looked closely at the fire bottles and couldn't find anything out of the ordinary. The levels were good.Taxi and takeoff were uneventful.On departure passing approximately 15;000 feet MSL the CA noticed the left engine overheat light flickered then went out. He tested the bulb and it tested good. I immediately went to the EGT (Exhaust Gas Temperature) gauges and noticed a 20-degree higher temperature on the left engine; but still well within limits. While I was looking at the EGT gauge the CA reported that the intermittent indications bounced back and forth between overheat and fault. When I looked down to study the light pattern the left engine fire light came on. We very briefly discussed that this seemed like an indication problem versus an actual fire/overheat; but we had to honor the lights in case there was something we could not see with other fire/overheat indications.The CA transferred aircraft control to me while he ran the checklist. I confirmed a level off with the CA and coordinated with ATC. We were initially assigned FL190; but we were already passing it; so I asked for FL200. I disengaged the autopilot and auto throttles anticipating correcting for single engine flight. The CA then confirmed the left engine immediate action items with me. I added right rudder and right rudder trim as the left engine spooled down. I coordinated with the CA and ATC for a left turn back to ZZZ along with a descent.Things got busy. I was manually flying; navigating; negotiating vectors and altitudes; and landing runway with ATC. The CA split his time then between running the checklist; paying attention to what I was doing; talking to the flight attendants; passengers; dispatch; and maintenance. I asked the CA if I should coordinate for holding and he said no. I began loading the approach for ZZZ ILS XXL; but did not execute until I could coordinate it with the CA. We went back and forth as to the best way to re-cruise the system. Eventually I just spun the cruise setting on the pressurization panel down to 7;000 ft.; and loaded 7;000 into the cruise page.Approaching abeam the field approximately 5;000 ft. the CA was ready to resume flying. He reloaded the approach; then asked me to extend the final approach fix ZZZZZ.We got an immediate descent and a 'tight' base vector abeam the final approach fix. There is a 'safety alert' when landing north on the Company Ops page that we were both aware of.The CA asked for the deferred items; but I did not have them up on my checklist. We were only about 8 miles out from the field at this point and in a great position to land; so the Captain decided it was better to continue at this point than go around. After realizing my checklist SA (Situational Awareness) was low and behind; I tried to keep the bigger picture safety of flight items in my cross check: aircraft configuration; energy state; threats from VFR aircraft at ZZZ1; and our approach into ZZZ.ZZZ approach kept us tight and close to ZZZ to avoid ZZZ1 traffic. We were given a 'dog-leg' to final that was going to have us intercept final inside the FAF. The final approach fix ZZZZZ is 8NM from the runway. We were told not to descend out of 2;600 ft.; until past the extended centerline forRunway XX/XY and cleared for the visual approach to Runway XXL. It was a beautiful VFR day; and we were visual with ZZZ and ZZZ1 15-20 miles out. I was occupied with searching for conflicting traffic at ZZZ1. The CA asked me to arm the approach; but it would not activate. We were also now busy configuring the gear and flaps to 15 and slowing to target speed. Rather than keep messing with the approach mode I announced we were past the conflict at ZZZ1 and visual to the correct runway and cleared to descend. We switched to tower and were cleared to land on Runway XXL.We used the normal landing checklist but modified it for our single engine approach.Final approach and landing were uneventful. We elected to exit off the runway and onto a taxiway to stop.The Tower gave us a ground frequency that the Fire Chief would also be on. We spoke to the fire department; and they checked out the aircraft and ran a thermal temperature sensor over the engines and the brakes. While they were doing that I talked to Company Ops about a gate. The fire chief declared the aircraft to be safe; so I coordinated to taxi back to the new gate.Upon engine shutdown at the gate; I noticed the left engine start level was not in cutoff.In retrospect; I should have advocated (or requested) to go into holding. It was not obvious at the time; but I had lost SA on what actions the CA had accomplished and where we were at in the checklist. It only became clear when on base he asked me for the 'deferred items' and I did not have them called up. The extra time would have allowed for a more thorough mind-meld. It would have also given us the opportunity to catch any checklist mistakes. I felt like we had a solid; simple plan to come back VFR to the long runway with a single engine approach. We got the aircraft and passengers back in a safe and efficient manner; but it felt rushed. It was only afterward that I recognized that the rushed feeling was self-imposed.


Second narrative: On preflight the fire test failed and ultimately the B loop was found to be inoperative. The B loop was deferred. A new Maintenance Release was obtained.On push back during the After Start Checklist recall we discovered that the zone temp lights for all three temperature zones were on but cleared when the master caution was pressed indicating a single temperature control failure. I noticed that the trim air switch was left in the on position during electrical transfer to the generators from the APU so we called Dispatch and Maintenance and the trim air system was placed on deferral. A new Maintenance Release was obtained.We proceeded normally to Runway XXR and departed normally. I was flying and the First Officer was Pilot Not Flying.On climb out above 15;000 feet we started getting master caution alerts over about a two minute period of time. The first was a number one engine over heat. Then we got a FAULT light on the fire control protection panel. Then a fire warning for the number one engine. All indications were temporary and went out on their own.The First Officer and I discussed what we were witnessing and decided that the safest course of action was to [advise ATC] and as a precaution; run the ENGINE FIRE OR ENGINE SEVERE DAMAGE OR SEPARATION checklist even though I highly suspected it was an indication problem with the fire control protection system. Factors supporting this decision were it was day VMC; we had just left ZZZ and we were both familiar with the airport having landed there the day prior.I [advised] with ATC and requested to return to ZZZ. The First Officer became the Pilot Flying and I assumed the Pilot Not Flying duties to run the checklist. The checklist was completed and the ONE ENGINE INOPERATIVE LANDING checklist was completed to deferred items.After talking with the First Officer after the flight I realized I skipped step 3 of the ENGINE FIRE OR ENGINE SEVERE DAMAGE OR SEPARATION checklist.... engine start lever confirm...cutoff. It was an honest mistake and not intentionally done.The flight attendants were given [the required] information. Dispatch was notified and a ELB entry was made. I made a PA announcement to the passengers informing them that we had to shut down the left engine and we were returning to ZZZ. I asked ZZZ approach to roll the fire trucks just in case we had an actual fire.Since we had just left ZZZ; we set up for a visual backed up with the ILS XXL approach. I briefed the approach and were set up for a single engine flaps 15 landing.Until this point I thought the flow of our checklists and coordination was comfortable and progressing well. I took controls of the aircraft to fly the approach but when I asked for the deferred items; the First Officer said he couldn't find the checklist on his iPad. I should have simply passed my iPad to him to complete the checklist but at the time I thought it would be just a brief amount of time until he had deferred items. Because we were day VMC and we were in a controlled good position I thought the safest course of action was to continue being vectored for landing and not extend on downwind. I elected to operate under my authority and continue towards ZZZ without having the First Officer read the Deferred Checklist items on the deferred portion of the checklist. I was also comfortable doing this because while running the checklist myself earlier; I glanced through the items ahead of time because they are located on the same page of the main checklist. It was not good crew coordination but I felt it was safer than extending out from where we currently were. We were in a good easy flowing path towards the runway and I elected to continue.We did land with the engine bleeds on which was a step on the deferred items of the ONE ENGINE INOPERATIVE LANDING checklist to turn them off and land bleeds off. This again was not intentional as my review of the deferral steps did not catch this correctly as I intended. As I said earlierthough I thought the best safest course of action was to continue the approach to a landing.ZZZ Approach vectored us for a visual and an intercept inside the FAF of [Runway] XXL because it is a long final over 5 miles long. I flew the visual to XXL and had the First Officer use the normal checklist card for the landing checklist. A normal landing was made and we stopped on the taxiway clear of the runway to allow the fire trucks to inspect the number one engine and for any potential hot brakes. Normal readings were found by the firemen and we taxied to the gate.Things that could have gone better:I did not explicitly say or remind the First Officer that we would be doing a flaps one go around if required in the brief and because we didn't run the deferred items of the one engine inoperative checklist we did not remind ourselves as the check list would have. At all times I knew that a flaps one go around would be accomplished; if required.I did not realize that the First Officer was feeling rushed and didn't have the checklist up to run on his own. I have been used to flying with more senior first officers and just assumed he would pull up the checklist on his own. Next time I will be more explicit in my instructions and anticipate getting both myself and the First Officer on the same page. I will make sure that the iPad that has the checklist being read from is continued to be used to finish deferred items if either pilot is not on the same page.I apologize for my errors made.


Synopsis: B737 flight crew reported engine overheat indications during departure climb. The crew returned to the departure airport and landed without incident.