Date: 201910
Local time of day: 1201-1800
Location: ZZZZ.Airport, FO
Aircraft: B747-400
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Cargo / Freight / Delivery
Flight phase: Parked
Aircraft component: Cargo Compartment Fire/Overheat Warning
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Captain
Reporter qualification: Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Human factors: Communication Breakdown
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Maintenance; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: Pre-flight
Result: General Maintenance Action
Contributing factors: Aircraft; Logbook Entry
Primary problem: Aircraft

Narrative: I was scheduled to operate a flight from ZZZZ. I spoke with one of the inbound Captains as I was leaving the hotel. When I asked him if there were any issues with the aircraft; he reported that the aircraft had an Aft Lower Cargo Compartment Fire indication on the previous flight either going into or on the ground at their intermediate stopover location. Additionally; he stated that the aircraft had the same issue multiple times on previous flights. When I got to the aircraft; one of the [mechanics] on the previous flight verified that they had experienced the Lower Aft Cargo Compartment Fire Indication and had placed the LLCCAFR switch in AFT High and reset circuit breakers and the fire indication went out. Upon reviewing the logbook; there was no write-up or corrective action regarding this event. The [mechanic] stated that he had performed numerous system tests following this event and that he believed there may be an issue with the test system since ACMS did not indicate an actual fire had occurred. A second [mechanic] on board then pointed out that ACMS trial software had been loaded on [Day 0] and all the issues with the fire indications had commenced after that date and he speculated that the new software may be causing an issue with the false indications. The aircraft had not exhibited a history of false fire indications prior to that date. The logbook also revealed that a Lower Aft Cargo Compartment Fire indication occurred on [Day 2] while in cruise.  I then reviewed and discussed the False Cargo Fire Warning Messages supplementary procedure in the FCOM with the other crew members. This SP was used for reference since it is applicable to [other aircraft] and not applicable to the aircraft we were operating. The SP addresses an issue where a humid environment could cause a false indication; however; this aircraft did not have a history of false indications prior to the new software and also the previous airfield was at a higher altitude in [another country] and therefore not necessarily a humid environment. After a lengthy discussion we did not believe that it was a safe decision to operate the aircraft with an unknown system malfunction present since all fire indications must be honored even if they were false. Knowing that even a false indication might cause a divert scenario in congested European airspace; we decided that it would be better to see if the detection system could be deactivated since there was no cargo in the lower aft compartment.Maintenance personnel reported that a write-up would have to be placed in the logbook before any corrective action could occur. I asked if the [mechanic] who had witnessed the previous event could do the write-up since he would be able to make a more accurate diagnosis having seen the issue first-hand. Maintenance Control directed that the [mechanic] would not make the write-up. After consultation with a Chief Pilot; I then put an entry in the logbook indicating what was relayed to me. The flight departed after maintenance personnel deactivated the lower aft compartment fire detection system and we arrived at our destination uneventfully.All events like this should be entered in the logbook so that troubleshooting and corrective action can be properly documented to provide an accurate aircraft history.




Synopsis: Captain reported that multiple false fire indications had not been recorded in the aircraft logbook and no documented corrective action taken.