An air carrier large transport had a false fire warning in the aft lavatory.

Attributes
ACN	245613
Time
Date	199307
Day	Thu
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : mbj
State Reference	FO
Altitude	msl bound lower : 12000 msl bound upper : 12000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zse
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 3 Turbojet Eng
Flight Phase	descent : approach descent other other
Route In Use	enroute airway : mbj
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : instrument pilot : atp pilot : commercial pilot : flight engineer
Experience	flight time last 90 days : 150 flight time total : 10000 flight time type : 4000
ASRS Report	245613
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial
Events
Anomaly	aircraft equipment problem : critical other anomaly other
Independent Detector	other other : unspecified
Resolutory Action	controller : issued new clearance flight crew : overcame equipment problem flight crew : declared emergency other
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	other

Narrative:

On descent into mbj, so received interphone call from flight attendant that 'there is a fire in the aft lavatory!' we were passing 12000 ft. I increased our rate of descent, and the first officer declared an emergency and requested clearance direct to the airport from mbj approach/tower. The so suggested, and I concurred, that he don the portable breathing equipment and go back and fight the fire. He did same and entered the cabin, only to return 15 seconds later advising that it was a false alarm. The first officer cancelled the emergency. It seems that the flight attendant, in spraying the cabin, also sprayed the aft biffy and closed that door. Shortly thereafter, that smoke alarm activated. A flight attendant responded, opened the door, saw and smelled smoke, took the halon bottle and sprayed the lavatory, while another flight attendant called the flight deck, declaring the fire. Within seconds, the flight attendant realized there was no fire and tried to recontact the flight deck by using the call button. The cockpit crew heard the call bell being rung, but due to the urgency of the situation and emergency activity by all 3 cockpit members, no one took time to answer the flight attendant's call. The so was advised of the current situation by the flight attendant after he entered the cabin.

Original NASA ASRS Text

Title: AN ACR LGT HAD A FALSE FIRE WARNING IN THE AFT LAVATORY.

Narrative: ON DSCNT INTO MBJ, SO RECEIVED INTERPHONE CALL FROM FLT ATTENDANT THAT 'THERE IS A FIRE IN THE AFT LAVATORY!' WE WERE PASSING 12000 FT. I INCREASED OUR RATE OF DSCNT, AND THE FO DECLARED AN EMER AND REQUESTED CLRNC DIRECT TO THE ARPT FROM MBJ APCH/TWR. THE SO SUGGESTED, AND I CONCURRED, THAT HE DON THE PORTABLE BREATHING EQUIP AND GO BACK AND FIGHT THE FIRE. HE DID SAME AND ENTERED THE CABIN, ONLY TO RETURN 15 SECONDS LATER ADVISING THAT IT WAS A FALSE ALARM. THE FO CANCELLED THE EMER. IT SEEMS THAT THE FLT ATTENDANT, IN SPRAYING THE CABIN, ALSO SPRAYED THE AFT BIFFY AND CLOSED THAT DOOR. SHORTLY THEREAFTER, THAT SMOKE ALARM ACTIVATED. A FLT ATTENDANT RESPONDED, OPENED THE DOOR, SAW AND SMELLED SMOKE, TOOK THE HALON BOTTLE AND SPRAYED THE LAVATORY, WHILE ANOTHER FLT ATTENDANT CALLED THE FLT DECK, DECLARING THE FIRE. WITHIN SECONDS, THE FLT ATTENDANT REALIZED THERE WAS NO FIRE AND TRIED TO RECONTACT THE FLT DECK BY USING THE CALL BUTTON. THE COCKPIT CREW HEARD THE CALL BELL BEING RUNG, BUT DUE TO THE URGENCY OF THE SIT AND EMER ACTIVITY BY ALL 3 COCKPIT MEMBERS, NO ONE TOOK TIME TO ANSWER THE FLT ATTENDANT'S CALL. THE SO WAS ADVISED OF THE CURRENT SIT BY THE FLT ATTENDANT AFTER HE ENTERED THE CABIN.

Data retrieved from NASA's ASRS site as of July 2007 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.