Date: 201706
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Daylight
Aircraft: B737-800
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Climb
Airspace: Class E ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Powerplant Fire/Overheat Warning
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Workload; Troubleshooting; Distraction
Second reporter function: Pilot Not Flying; First Officer
Anomaly: Aircraft Equipment Problem Less Severe
Detector: Automation Aircraft Other Automation; Person Flight Crew
When detected: In-flight
Result: Flight Crew FLC complied w / Automation / Advisory; Flight Crew Landed in Emergency Condition; Flight Crew Returned To Departure Airport; General Maintenance Action
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: I was the Pilot Flying (PF) on the subject flight. After takeoff; the Fire Fault Light intermittently flickered; flashed; and on steady passing 10;000 feet. At that point; I took both the aircraft and radios and the Pilot Monitoring (PM) performed the QRH. We determined that there was nothing to be done. Our Fire Detection System was to be considered completely or partially failed and no way to determine that extent. I sent multiple free test messages to dispatch to have them contact Maintenance to see if we had overlooked anything and if there was a way to continue the flight. Maintenance wanted to verify A or B systems. That could not be done as the light was flashing and we could not catch the flash; further; that was not an inflight procedure in our approved QRH. I sent the message that we felt we were not legal to continue and a return to the departure airport was in order. Dispatch responded in agreement. During all this time; we continued to fly west and burn fuel. I felt this would lighten our ultimate overweight landing and maximize our set-up time for the return. I specifically told ATC that the Fire Fault Light was on. The PM did the runway landing analysis. As a result of that; I elected to request and land on runway XYR just in case we had fading brakes due to the landing weight of 151;600 pounds. I briefed the flight attendants on the issue; assured them of a normal approach and landing. I also informed them that our fire detection system was in doubt and they should inform me of any visually detected fire outside the plane. I then told the passenger that we had a minor malfunction and would return. I also told them that because of the heavy landing; emergency personnel would meet the plane near the runway to ensure our brakes were cool enough to return to the gate. We briefed and flew the ILS to XYR landing with flaps 30 and brakes 3. Airport Rescue and Fire Fighting (ARFF) verified on the discreet frequency that our brake temperature was safe for a return to the gate. Flight was terminated without further incident.


Second narrative: I was the PM on the subject flight. After takeoff and at around 10;000 feet AGL the Engine Fire/Overheat Detector Fault Light flickered intermittently and then came on steady. The PF then took the aircraft and radios and I as the PM ran the ORH procedure. The QRH stated that the light signified that Engine Overheat and Engine fire detection is inoperative in one or both engines. We continued the flight as we assessed the situation and sent a message to dispatch to inform them of our situation and ask them to contact the Maintenance. After ACARS communication with dispatch and reference to the QRH it was determined that we would return to the departure airport. We determined we would be landing 7;600 pounds overweight upon arrival and did a runway analysis. The analysis figured we would need 7;966 feet to land at our determined landing weight of 151;600 Lbs. Our assigned runway was XYC which is 10;000 feet and we ask for the longer runway XYR which is 13;000 feet for less stress on the brake system. We ask for AARF to be available upon landing and landed without incident on XYR and exited off the runway. ARRF checked our brakes and wheels for overheating and then cleared us to taxi to gate. AARF followed us to our gate and we parked without incident.


Synopsis: B737-800 flight crew reported the Engine Fire/Overheat Detector Fault Light illuminated in climb; resulting in a return to the departure airport.