A B757's forward lavatory smoke alarms sounded as the aircraft was flying down wind for landing so t...

Narrative:

On extended downwind to runway 22 we began getting lavatory smoke alarms in the forward lav and the left aft lav accompanied by large fluctuations in the bleed duct pressure the flight attendants could not see or smell any smoke however. I began to think along the lines of a bleed leak. I decided to declare an emergency and make an immediate landing on 31. After landing I had the aircraft inspected by the responding airport rescue and fire fighting crews. They did not find any hotspots so after consulting with maintenance I decided to restart the engines (they had been secured at the request of the airport rescue and fire fighting crew) and taxi to the gate. Shortly after the bleed ducts were pressurized to start the engines the lavatory smoke detectors went off again. I completed the engine start and closed the bleeds silencing the smoke alarms.

Original NASA ASRS Text

Title: A B757's forward lavatory smoke alarms sounded as the aircraft was flying down wind for landing so the Captain diverted and landed on the nearest runway where Airport Rescue and Fire Fighting could find no heat sources. The alarms ceased with engine bleeds off but resumed when bleeds were opened.

Narrative: On extended downwind to Runway 22 we began getting lavatory smoke alarms in the forward lav and the left aft lav accompanied by large fluctuations in the bleed duct pressure the flight attendants could not see or smell any smoke however. I began to think along the lines of a bleed leak. I decided to declare an emergency and make an immediate landing on 31. After landing I had the aircraft inspected by the responding Airport Rescue and Fire Fighting crews. They did not find any hotspots so after consulting with maintenance I decided to restart the engines (they had been secured at the request of the Airport Rescue and Fire Fighting crew) and taxi to the gate. Shortly after the bleed ducts were pressurized to start the engines the lavatory smoke detectors went off again. I completed the engine start and closed the bleeds silencing the smoke alarms.

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	931652
Time
Date	201102
Local Time Of Day	1201-1800
Place
Locale Reference	ZZZ.ARTCC
State Reference	US
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Make Model Name	B757-200
Operating Under FAR Part	Part 121
Flight Phase	Initial Approach
Flight Plan	IFR
Component
Aircraft Component	Toilet Smoke Overheat Fire Detectors & Warning
Person 1
Function	Captain
Qualification	Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	Aircraft Equipment Problem Critical Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor

A B757's forward lavatory smoke alarms sounded as the aircraft was flying down wind for landing so the captain diverted and landed on the nearest runway where airport rescue and fire fighting could find no heat sources. The alarms ceased with engine bleeds off but resumed when bleeds were opened.