A B747-400 captain reported spurious main cargo compartment fire warnings. The spurious signals appe...

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 referred to the QRH; however; this item had been previously written up on several legs before this flight. Also of note; several smoke detectors were 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: heat valve; fans; etc. Continuing to our destination; we declared an emergency and upon landing requested an exterior inspection by crash fire rescue equipment. 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: A B747-400 Captain reported spurious main cargo compartment fire warnings. The spurious signals appeared to be chronic maintenance items. A precautionary emergency was declared on landing and a CFR inspection proved negative.

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 referred to the QRH; however; this item had been previously written up on several legs before this flight. Also of note; several smoke detectors were 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: heat valve; fans; etc. Continuing to our destination; we declared an emergency and upon landing requested an exterior inspection by CFR. 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	967080
Time
Date	201108
Local Time Of Day	0001-0600
Place
Locale Reference	ZZZ.Airport
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
Flight Plan	IFR
Component
Aircraft Component	Cargo Compartment Fire/Overheat Warning
Person 1
Function	Captain Check Pilot
Qualification	Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	Aircraft Equipment Problem Less Severe

A B747-400 captain reported spurious main cargo compartment fire warnings. The spurious signals appeared to be chronic maintenance items. A precautionary emergency was declared on landing and a crash fire rescue equipment inspection proved negative.