B747-400 cargo fire alerted at cruise but the crew determined it was a false warning. Before landing...

Narrative:

I was summoned to the cockpit because of an intermittent main deck cargo fire indication. The event consisted of the warbler; the master warning and a light in the overhead 'arm' switch. No EICAS message illuminated. We; as a crew referred to the QRH; however; this item had been previously written up on several legs before this flight. Also of note: several smoke detectors where on deferral. An inspection of the main deck revealed no sign of smoke; heat or flames. There was no declared hazmat on board the aircraft. An inspection of the cargo documents revealed no additional items of interest. I contacted dispatch. The conference included dispatch and maintenance. All involved in the discussion concurred that the problem was a spurious signal. Main deck inspections occurred at close intervals for the remainder of the flight. No smoke or fire was ever reported. No EICAS message illuminated. Also during this time period several items in the aft bulk cargo failed. Ie: heat valve; fans; etc. Continuing to our destination we declared an emergency and upon landing requested and exterior inspection from the fire department. No anomalies were found. Again we inspected the main deck and found no trace of smoke or fire. We continued to the gate without further issues.

Original NASA ASRS Text

Title: B747-400 Cargo Fire alerted at cruise but the crew determined it was a false warning. Before landing the Captain declared an emergency as a precaution.

Narrative: I was summoned to the cockpit because of an intermittent main deck cargo fire indication. The event consisted of the warbler; the Master Warning and a light in the overhead 'ARM' switch. No EICAS message illuminated. We; as a crew referred to the QRH; however; this item had been previously written up on several legs before this flight. Also of note: several smoke detectors where on deferral. An inspection of the main deck revealed no sign of smoke; heat or flames. There was no declared HAZMAT on board the aircraft. An inspection of the cargo documents revealed no additional items of interest. I contacted Dispatch. The conference included Dispatch and Maintenance. All involved in the discussion concurred that the problem was a spurious signal. Main deck inspections occurred at close intervals for the remainder of the flight. NO smoke or fire was ever reported. NO EICAS message illuminated. Also during this time period several items in the aft bulk cargo failed. IE: heat valve; fans; etc. Continuing to our destination we declared an emergency and upon landing requested and exterior inspection from the fire department. No anomalies were found. Again we inspected the main deck and found no trace of smoke or fire. We continued to the gate without further issues.

Data retrieved from NASA's ASRS site as of April 2012 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.

Attributes
ACN	966899
Time
Date	201108
Local Time Of Day	0001-0600
Place
Locale Reference	ZZZ.ARTCC
State Reference	US
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Make Model Name	B747-400
Operating Under FAR Part	Part 121
Flight Phase	Cruise
Route In Use	Oceanic
Flight Plan	IFR
Component
Aircraft Component	Cargo Compartment Fire/Overheat Warning
Person 1
Function	Check Pilot Pilot Not Flying Captain
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 150 Flight Crew Total 16000 Flight Crew Type 6000
Events
Anomaly	Aircraft Equipment Problem Less Severe

B747-400 cargo fire alerted at cruise but the crew determined it was a false warning. Before landing the captain declared an emergency as a precaution.