B737 flight crew reported the fire detection system malfunctioned after takeoff. The flight crew performed an air turn back and precautionary landing at departure airport.
Synopsis
B737 flight crew reported the fire detection system malfunctioned after takeoff. The flight crew performed an air turn back and precautionary landing at departure airport.
Narrative
It was the First Officers (FO's) takeoff off of XXL in ZZZ. Everything was fine until we reached V1. As soon as my hand was a few inches off of the throttles; the fire warning horn and lights were going off everywhere. We were just past V1 so we were in go mode. As soon as I got the gear up and saw the aircraft was under control I looked down to see what all was lit up. We had both master caution lights; both fire warning lights; the fire bell; both engine 1 and 2 overheat lights; engine 1 and 2 fire handles lit up; the APU fire handle lit up and the wheel well fire light lit up. I immediately [requested priority handling] and told them we wanted to climb to 2500 ft. while entering a left downwind and base and land back on XXL. The FO was very sharp and I asked them if they felt comfortable doing that on their own while I worked the problem. They were fine and I kept an eye on the plane and our position while getting into the checklist. I went straight to the wheel well fire checklist because I felt that was our biggest threat. Both engines were running normal and no abnormal indications and the APU was off so I thought the wheel well could be on fire or have bad indications. I gave souls on board; fuel in minutes; stated our intentions and asked them to relay our situation to our company. I did the QRH; we quickly set up for the approach and turned base for XXL.I tested the lead Flight Attendant (FA) and gave a very brief PA to the passengers; ran the descent and landing checklists and landed and stopped on taxiway x. We shut both engines down and Crash Fire Rescue (CFR) said all indications were normal and no abnormal heat anywhere. We got a gate from ops; started the engines and taxied to gate. Before we taxied onto the J-line I had them check the temps again and then we taxied in and de-boarded the people. After we re-started both engines I went to put the generators online and generator 2 started the fire bell and warning lights again. Generator 1 did not trip it. I put it on the APU and it did the same thing. I went back to the engine driven generators and same thing and again went back to the APU. When we went to ground power at the gate it did the same thing with the horn and lights. From there I wrote everything up and talked to Dispatch; Maintenance at ZZZ; Ops and the Chief Pilot. From there I made sure the passengers in the terminal were taken care of and then took care of the crew. We all went to the hotel for a much needed rest. I have no idea what set all of this in motion but I thought the crew; ATC; Airport Rescue and Firefighting (ARFF); Ops; Dispatch; Maintenance and the Chief Pilot all did their jobs very well.
Second reporter narrative
On takeoff roll saw fire master warning light right at V1. Captain said to continue so preceded to rotate at Vr. Once airborne we saw that we had all 3 fire handles illuminating along with the wheel well fire light and both engine overheat lights. The Captain said they smelled something when we brought the gear up but since we had all those lights we were not sure how to diagnose. We announced the situation at about 1500 ft. and I told the Captain to let Tower know I was turning left into the downwind. The Captain pulled the wheel well fire checklist since we did not have any secondary engine fire indications. I hand flew the aircraft at pattern altitude while the Captain ran the checklist and communicated with Tower. Once the checklist was complete I turned final and asked for final flaps with the landing checklist. I verified we were cleared to land and had an uneventful landing. We taxied off the runway and were inspected by the Crash Fire Rescue (CFR) before confirming that we were free from fire and getting a gate to taxi back into. As a crew; the Captain and I had really good communication and delegation of duties. I focused on the flying and kept the runway in sight and was ready to turn in for landing as soon as we were finished with our checklist. We had talked about what indications we were seeing and were able to quickly come up with a diagnosis and direction to a checklist. The Captain did a good job of coming in and out of the checklist when I was requesting configuration to remain close to the field. They also had a good suggestion for me to keep in the back of my mind when I touched down to be cautious of blown tires since we did not know if we had an actual wheel well fire or not at that point. Once on the ground we did a good job of communicating with Ground and CFR while keeping the crew and passengers informed of progress. Debriefing it together the only thing we could come up with that we could have done differently would have been to not raise the gear in case it was a wheel well fire. At the time; we were pretty sure it was an electrical issue due to the fact that so many lights had illuminated. What I would have done differently would have been to get flaps 5 with flaps 5 speed sooner to keep my pattern tighter and give more time for the checklist.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.