Date: 201306
Local time of day: 0001-0600
Location: ZZZ.ARTCC, US
Flight conditions: VMC
Light: Night
Aircraft: B747 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Cargo / Freight / Delivery
Flight phase: Cruise
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Cargo Compartment Fire/Overheat Warning
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Flight Instructor
Human factors: Distraction; Situational Awareness; Time Pressure; Troubleshooting; Workload
Anomaly: Aircraft Equipment Problem Critical
Detector: Automation Aircraft Other Automation; Person Flight Crew
When detected: In-flight
Result: Flight Crew Diverted; Flight Crew Landed in Emergency Condition; Flight Crew Took Evasive Action; General Declared Emergency; General Maintenance Action
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: Approximately 35-40 minutes into the flight at cruise altitude of FL330 a status message appeared on lower EICAS; CARGO SMOKE DETECTION. A closer look at this message showed Cargo Smoke Detection Aft Lower Lobe detector 28 had failed. I printed this message from CMC and forwarded the message to company on ACARS. About 15 minutes later; or 1 hour into the flight; while standing in the galley; I heard a fire bell go off and walked back into cockpit to see the Master Warning in red appear FIRE CARGO AFT. This EICAS message remained on for about 2 seconds then disappeared. The pilot flying the aircraft; First Officer; had already informed ATC (Center) that we may have a problem and would advise ATC shortly. Immediately following the fire warning the First Officer and I had discussed a diversion and determined an ocean crossing was not an option. The EICAS message had disappeared and I decided to call the company on SATCOM to advise that we would need to make arrangements to land the aircraft due this intermittent cargo fire warning. As I was speaking to the Duty Manager in Operations on the SATCOM; the FIRE AFT CARGO master warning and fire bell went off again; and again the message disappeared and the fire bell went out after 2 or 5 seconds.  A distant major airport was discussed as a diversion point but too far considering time and distance with the fire-warning situation; and since another mojor airport was about 80 miles ahead; it was decided to divert there. The First Officer had advised ATC and declared an emergency and we advised that we would divert. The First Officer flew the aircraft and did initial communications with ATC. I changed the destination in the route page and selected XXL for that airport. Initially we were cleared to 10;000 feet from FL330. The First Officer flew the aircraft and did the communication while I set up the boxes and worked the QRH emergency checklist. The weight of the aircraft was determined to exceed maximum landing weight; and jettisoning fuel was commenced shortly after the descent began from FL330. The approximate fuel at this time was 85.0 and to be at max landing weight of 346.1; it was determined that fuel remaining on approach would have to be 40.0 tons or less to not exceed max landing weight. On the descent to 10;000 feet the FIRE CARGO AFT warning and fire bell went off several times; however; extinguished after 2 or 3 seconds. The same fire warning came every 2 minutes while in the descent; however; it would go out after 2 to 3 seconds. This annoying situation continued for the remainder of the approach and landing. While the First Officer continued to fly the aircraft with good forward speed; the second First Officer and I ran the QRH; and I decided to finally ARM the Aft Cargo Fire switch at 15 miles distance from [our destination]; basically on a base leg to Runway XXL; I asked the second First Officer to press and hold the Cargo Fire DEPRESS/DISCH switch to activate the Halon Fire agent into the Aft Cargo Area. With the short time and distance remaining before we landed at [our destination] we dumped fuel from 85.0 to 67.0; which would be a landing weight of 372.0 tons or an overweight landing condition. Flaps 30 were selected for the landing and 169 knots was the final approach speed; with an autobrake setting of 4. ATC had cleared us direct and later vectored us west of [the airport] on a right downwind to Runway XXL. As we approached ZZZ the fuel synoptic indicated that it would require an additional 17 minutes of flying time to dump to a level of 40 tons or max landing weight. Considering this annoying FIRE CARGO AFT fire warning and bell was becoming more frequent and then disappearing; we proceeded to continue to with the 372.0 weight landing. As we descended though 7;000 feet I discontinued the fuel dumping. The aircraft was approximately 12-15 miles north of the airport when we were given final vectors to the visual/ILS for XXL and the runway was in sight.ATC had been advised that I had requested fire equipment standing by the runway; and this was confirmed when we switched to the Tower frequency. I also advised the Tower that the lower cargo areas were not to be opened until the passengers and crew had exited the aircraft. The aircraft landed on XXL very smoothly and the auto-brakes decelerated the aircraft with a normal deceleration rate; and the auto-brakes were disconnected at 75 knots. The aircraft exited XXL at K-7 into a wide area that would allow the CFR equipment to surround the aircraft. Communication was established with Ground frequency as well as CFR through the cockpit to ground connection. My concern was to clear Runway XXL into an area wide enough to have room enough to access equipment.  In the event of brake heating; I didn't want to have the disabled aircraft remaining on the Runway XXL if the fuse plugs melted. This K-7 area served this requirement. After we parked at K-7 my concern was get the aircraft chocked immediately so I would be able to release the parking brake and allow brake cooling. The wheels synoptic showed all brakes temperatures between 5.2 and 5.7. The CFR through cockpit to ground communication confirmed chocks on nose gear and I released the parking brakes. The temps never exceed 5.7 and prior to moving the aircraft from K-7 to R-11 the brakes cooled to a level no greater than 2.2. The CFR personnel were aware of potential tire burst or fuse plugs and tracked the temperatures as high as 400F. The APU was started prior to engine shutdown to and when selected ON; I shut down all 4 engines. The crew exited the aircraft shortly after engine shutdown. The evacuation had been discussed and I decided NOT to use the escape slides after the CFR had determined no visual fire and/or smoke. The evacuation was coordinated with the CFR personnel through the 1L door; utilizing a ladder extended horizontally from a fire truck to the 1L door. This ladder was used as a horizontal walkway for the crew and passengers to exit the aircraft holding onto the handrails and walking on the rungs. All 6 crew and passengers exited the aircraft carefully and remained at a safe distance while the CFR personnel opened the Aft Cargo Door; followed by the Forward Cargo Door and the Bulk Cargo door. The CFR personnel entered and visually inspected these areas and determined there had been no evidence of any fire; and the areas were safe. I arranged a hotel for the crew members and passengers; and had the crew members leave the aircraft. A people mover was used to exit the passenger and crew to the main terminal. I remained at the aircraft for at least 2 more hours and began to write a summary of events on my iPad. I waited until the (Load master) arrived; and while departing the airport I met with Maintenance Representative; maintenance from WRI; and escorted him back to the aircraft where I de-briefed Maintenance on the overweight landing and the sequence of events with the FIRE CARGO AFT warnings and bell. I discussed the details of the warning and continued frequency of the warnings; even after landing and re-positioning the aircraft. During the descent; approach and landing this FIRE CARGO AFT warning and fire bell went off every 1 to 2 minutes and disappeared within 1 to 2 seconds. This continued even after the Halon Agent was discharged into the Aft Cargo area. The fire light and warning never appeared for more than 1-2 seconds and it never remained on steady during this whole event from initial indication at 1 hour elapsed time of the flight. I thought that this had to be related to the earlier status message with respect to Aft Cargo Lobe Detector 28 Failure. These warnings were too coincidental and I believe this detector #28 failure may have caused these multiple FIRE CARGO AFT warnings and fire bells that would appear and vanish within 1 or 2 seconds. These FIRE CARGO AFT warning and fire bells continued after the CFR had cleared the Aft Cargo Area; aswell as the; Forward and Bulk cargo areas. The warnings continued for the next 2 hours and crewmembers took photos of the upper EICAS with the warning and then the warning would disappear. After the crew had departed the aircraft this FIRE AFT CARGO continued to appear for another 2 hours; while I was compiling notes on my iPad sitting in the cockpit. Speaking to a dead heading Captain on the flight; after the flight; he mentioned that the FIRE CARGO AFT warning remained for up to several minutes while the aircraft was on the ground after the CFR had determined all cargo areas were clear.




Synopsis: A B747 Cargo Fire Warning alerted at cruise; so an emergency was declared and the flight diverted to an enroute airport where a false warning was confirmed by the Airport Rescue and Fire Fighters.