Narrative:

On the initial climb out of ZZZZ the upper EICAS had the advisory 'det fire engine left'; which lasted for approximately 3 minutes. After contacting dispatch/maintenance control we had two lower EICAS status messages: 'overheat circuit L2 ' and 'fire loop 2 eng left' which appeared for about 1 minute (additionally the left engine vibration system was previously deferred inop). We referred to flight manual guidance which only advised that fire and overheat detection was inop. At best we had intermittent fire/overheat detection on the left engine with no guidance in the event of total system failure.after discussing the messages with maintenance control/dispatch; operations manager; crew and I decided that the fire detection on the left engine was possibly intermittent and as such; undependable. If we had gone oceanic and the messages reappeared; or new messages concerning the fire detection system appeared I would consider the system undependable and unable to detect an engine fire - making a divert to the closest alternate necessary. After relating this to maintenance control/operations manager/dispatch I was told that it would be preferable to divert to ZZZZ2 where there was a 'fire card' that could fix the issue. We coordinated with center and turned towards ZZZZ2 after dumping 45;000 lbs. Of fuel. Subsequently dispatch contacted us and through satcom communications and told us that a 'company' NOTAM prohibited us from going to ZZZZ2 unless we declared an emergency. We requested center to ask ZZZZ2 if we could land at ZZZZ2 without declaring an emergency. The answer was yes. Despite being allowed to land at ZZZZ2; dispatch refused to release us. Instead dispatch directed us to go to ZZZZ [our departure airport]- to go to ZZZZ2 we would need to declare an emergency. We assumed that all involved in the satcom discussion (operations manager; maintenance control; dispatch) were in agreement or that they saw ZZZZ as a better divert for the passengers. After the decision to divert to ZZZZ we sent messages to ZZZZ ops and the operations manager. It later came to our attention that ZZZZ had not been advised until just before our return to ZZZZ. We also learned that maintenance control and dispatch had not advised ZZZZ of the divert change (ZZZZ2 to ZZZZ). We also were told that maintenance control had a shift change and did not relay the diversion change to ZZZZ.I was surprised that an entire engine fire/overheat detection system could be inop and no guidance given! Also; that the APU fire detection also ran through this card - I assume this would mean that in the event of a card failure that the APU would not start- another system/redundancy unavailable! Why is there no guidance of what to do if the fire detection system is inop? Is it expected that someone would sit by a window and watch the engine for flames the entire flight. The company NOTAM for ZZZZ2: if ZZZZ2 rescinds the requirement of declaring an emergency to be able to divert into ZZZZ2 is that flight in violation of the NOTAM? Was dispatch correct in refusing to release us to ZZZZ2?

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Original NASA ASRS Text

Title: B777 flight crew reported managing a defective fire detection system on one engine after takeoff and the subsequent problems that occurred after the divert.

Narrative: On the initial climb out of ZZZZ the upper EICAS had the advisory 'DET FIRE ENG L'; which lasted for approximately 3 minutes. After contacting Dispatch/Maintenance Control we had two lower EICAS status messages: 'Overheat Circuit L2 ' and 'Fire Loop 2 Eng L' which appeared for about 1 minute (Additionally the left engine vibration system was previously deferred inop). We referred to flight manual guidance which only advised that fire and overheat detection was inop. At best we had intermittent fire/overheat detection on the left engine with no guidance in the event of total system failure.After discussing the messages with Maintenance Control/Dispatch; Operations Manager; crew and I decided that the fire detection on the left engine was possibly intermittent and as such; undependable. If we had gone oceanic and the messages reappeared; or new messages concerning the fire detection system appeared I would consider the system undependable and unable to detect an engine fire - making a divert to the closest alternate necessary. After relating this to Maintenance Control/Operations Manager/Dispatch I was told that it would be preferable to divert to ZZZZ2 where there was a 'fire card' that could fix the issue. We coordinated with Center and turned towards ZZZZ2 after dumping 45;000 lbs. of fuel. Subsequently Dispatch contacted us and through satcom communications and told us that a 'company' NOTAM prohibited us from going to ZZZZ2 unless we declared an emergency. We requested Center to ask ZZZZ2 if we could land at ZZZZ2 without declaring an emergency. The answer was yes. Despite being allowed to land at ZZZZ2; Dispatch refused to release us. Instead Dispatch directed us to go to ZZZZ [our departure airport]- to go to ZZZZ2 we would need to declare an emergency. We assumed that all involved in the satcom discussion (Operations Manager; Maintenance Control; Dispatch) were in agreement or that they saw ZZZZ as a better divert for the passengers. After the decision to divert to ZZZZ we sent messages to ZZZZ ops and the Operations Manager. It later came to our attention that ZZZZ had not been advised until just before our return to ZZZZ. We also learned that Maintenance Control and Dispatch had not advised ZZZZ of the divert change (ZZZZ2 to ZZZZ). We also were told that Maintenance Control had a shift change and did not relay the diversion change to ZZZZ.I was surprised that an entire engine fire/overheat detection system could be inop and no guidance given! Also; that the APU fire detection also ran through this card - I assume this would mean that in the event of a card failure that the APU would not start- another system/redundancy unavailable! Why is there no guidance of what to do if the fire detection system is inop? Is it expected that someone would sit by a window and watch the engine for flames the entire flight. The company NOTAM for ZZZZ2: if ZZZZ2 rescinds the requirement of declaring an emergency to be able to divert into ZZZZ2 is that flight in violation of the NOTAM? Was Dispatch correct in refusing to release us to ZZZZ2?

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.