Narrative:

After departure; at approximately 5;000 ft; [I] selected full power. Seconds later; I heard 'B' flight attendant call 'a' and report smoke in cabin and lavatory fire alarm on. (I was monitoring service interphone.) I got online and told them to stay on and report any change and I would be listening. I then told first officer the situation and asked him to tell ATC; we were returning and declaring an emergency. Then; I assumed the radio; and we did boxed QRH items and he began to run QRH; while I placed aircraft on autopilot and used radios. We performed most all items; and as we got to recirculation (recirc) fan off; 'B' flight attendant reported smoke dissipating. I then directed first officer to help me prepare for landing. He pointed out it would be an overweight landing by about 700 pounds. That was noted and later entered into logbook. Approach and landing were uneventful and arff followed us to gate. I then asked passengers to remain seated and allow arff to use ir detector to check for hot spots. None were found; and they went to cargo and exterior to check there; and we deplaned passengers. Fortunately; a maintenance crew was there to work on another aircraft and was able to work [our] problem. They discovered one disconnected duct and another unwrapped duct. They also MEL'd recirc fan; and swapped out lavatory fire detection units; which leads to another report concerning the next flight.

Related reports:

Google
 

Original NASA ASRS Text

Title: B737-300 Captain is informed of smoke in the cabin by a Flight Attendant during initial climb after takeoff. The QRH is complied with; and emergency is declared and the flight returns to the departure airport. After maintenance action is performed the flight departs a second time and the scenario repeats in its entirety.

Narrative: After departure; at approximately 5;000 FT; [I] selected full power. Seconds later; I heard 'B' Flight Attendant call 'A' and report smoke in cabin and lavatory fire alarm on. (I was monitoring service interphone.) I got online and told them to stay on and report any change and I would be listening. I then told First Officer the situation and asked him to tell ATC; we were returning and declaring an emergency. Then; I assumed the radio; and we did boxed QRH items and he began to run QRH; while I placed aircraft on autopilot and used radios. We performed most all items; and as we got to recirculation (recirc) fan off; 'B' Flight Attendant reported smoke dissipating. I then directed First Officer to help me prepare for landing. He pointed out it would be an overweight landing by about 700 LBS. That was noted and later entered into logbook. Approach and landing were uneventful and ARFF followed us to gate. I then asked passengers to remain seated and allow ARFF to use IR detector to check for hot spots. None were found; and they went to cargo and exterior to check there; and we deplaned passengers. Fortunately; a maintenance crew was there to work on another aircraft and was able to work [our] problem. They discovered one disconnected duct and another unwrapped duct. They also MEL'd recirc fan; and swapped out lavatory fire detection units; which leads to another report concerning the next flight.

Data retrieved from NASA's ASRS site 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.