Narrative:

This was leg 1 of day 1 of our work week of flying. The flight had followed normal procedures; practices; and expectations from preflight through initial climb. I was pilot flying on this leg and the captain was pilot monitoring. We were communicating with ZZZ center and given our final climb clearance to filed cruise altitude of FL360. Climbing through approximately FL250 we received an aural alert accompanied by the master warning and both fwd cargo fire and aft cargo fire eicas messages. We both acknowledged the warning and tried to assess the gravity of the situation. There was enough time for me to glance at the center console and see the fwd and aft cargo fire lights illuminated there as well and then the aural warning went away followed by the visual warnings. We had not accomplished any actionable QRH items at this point and at this point we had to reassess and the captain offered that we don't know for sure why the warnings started or ended but we were closer to ZZZ and this is an issue better sorted out on the ground to which I agreed. We were passing through approximately FL280 when the captain advised ATC and requested a return to ZZZ. The controller was quick acting and gave us a right turn and descend to FL230 I think. We eventually received further clearance to descend to 2;000 and join the ILS xxr approach from the zzzzz intersection with the captain still in the pilot monitoring role. The approach controller offered runway xxc but we both concluded that landing on ruwnay xxr was still prudent and safe. We descended in flch at some speed close to the zipper for most of the descent; we confirmed flight above 250 kts below 10;000 feet with ATC; we started configuring and the captain and I switched pilot roles somewhere outside of zzzzz. The switch wasn't pre briefed but seemed organic to the situation with landing weight and all other factors and so I continued as pilot monitoring from that point. We landed runway xxr and exited taxiway X and the only issue we encountered was communicating with the fire rescue on frequency. We could communicate with tower effectively however; we could hear rescue talk but they could not seem to hear our response. This was from both the captain and my side of the radios. The rest of the taxi in was uneventful.we are not aware of the cause; we just responded to fire warnings and thought returning and sorting it out on the ground was safer than sorry.

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Original NASA ASRS Text

Title: B757 flight crew performed an air turnback after receiving Fire Warning indication for both cargo compartments.

Narrative: This was leg 1 of day 1 of our work week of flying. The flight had followed normal procedures; practices; and expectations from preflight through initial climb. I was pilot flying on this leg and the Captain was pilot monitoring. We were communicating with ZZZ center and given our final climb clearance to filed cruise altitude of FL360. Climbing through approximately FL250 we received an aural alert accompanied by the master warning and both FWD CARGO FIRE and AFT CARGO FIRE Eicas messages. We both acknowledged the warning and tried to assess the gravity of the situation. There was enough time for me to glance at the center console and see the FWD and AFT Cargo fire lights illuminated there as well and then the aural warning went away followed by the visual warnings. We had not accomplished any actionable QRH items at this point and at this point we had to reassess and the Captain offered that we don't know for sure why the warnings started or ended but we were closer to ZZZ and this is an issue better sorted out on the ground to which I agreed. We were passing through approximately FL280 when the Captain advised ATC and requested a return to ZZZ. The Controller was quick acting and gave us a right turn and descend to FL230 I think. We eventually received further clearance to descend to 2;000 and join the ILS XXR approach from the ZZZZZ intersection with the Captain still in the pilot monitoring role. The approach controller offered Runway XXC but we both concluded that landing on Ruwnay XXR was still prudent and safe. We descended in FLCH at some speed close to the zipper for most of the descent; we confirmed flight above 250 kts below 10;000 feet with ATC; we started configuring and the Captain and I switched pilot roles somewhere outside of ZZZZZ. The switch wasn't pre briefed but seemed organic to the situation with landing weight and all other factors and so I continued as pilot monitoring from that point. We landed Runway XXR and exited taxiway X and the only issue we encountered was communicating with the fire rescue on frequency. We could communicate with Tower effectively however; we could hear rescue talk but they could not seem to hear our response. This was from both the Captain and my side of the radios. The rest of the taxi in was uneventful.We are not aware of the cause; we just responded to fire warnings and thought returning and sorting it out on the ground was safer than sorry.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.