AN EMB145 ON TKOF CLB AT 1800 FT DECLARED AN EMER AND RETURNED TO THE DEP ARPT DUE TO EICAS WARNING 'LAVATORY SMOKE.' CABIN ATTENDANT CONFIRMED SMELL OF SMOKE AND LAVATORY SMOKE ALARM ACTIVATED.

Narrative

I WAS CAPT ON AN EMB145. THE ACFT HAD THE LAVATORY ON MEL AND IT WAS LOCKED AND CLOSED BY MAINT AS INSTRUCTED BY THE MEL. AFTER PUSHBACK WE STARTED #1 ENG AND WE HAD AN EICAS MESSAGE 'ICE DETECTORS FAILED' AND 'ICE DETECTOR 1-2 FAIL.' WE PULLED THE MEL BOOK AND ACCORDING TO IT; ONLY ONE COULD BE INOP. WE CALLED MAINT AND RETURNED TO THE GATE. MAINT DID A COMPLETE PWR DOWN AND RESET TO FIX THE FAULT. THE FAULT WAS FIXED. WE DEPARTED THE GATE SINGLE ENG TAXI TO RWY 35L. WHEN WE STARTED THE #2 ENG; WE HAD AN EICAS CAUTION MESSAGE OF 'E1-2 NO DISPATCH.' I ADVISED TWR THAT WE NEEDED A FEW MINS TO RUN A PROC THAT ALSO REQUIRED TO SHUT DOWN AND RESTART BOTH ENGS. FLT ATTENDANT; PAX AND MAINT WERE ALSO NOTIFIED. WE PROCEEDED WITH THE E1-2 NO DISPATCH PROC AND THE RESET WAS SUCCESSFULLY COMPLETED. ABOUT XA50 WE ROTATED FROM RWY 35L. IT WAS A NORMAL TKOF. AT APPROX 1800 FT MSL EICAS MASTER WARNING APPEARED INDICATING LAVATORY SMOKE. THE FO WAS FLYING THE ACFT AND CONTINUED TO DO SO WHILE I WAS DOING THE EMER CHKLIST. I ADVISED THE FLT ATTENDANT IF SHE HAD ANY INDICATION OF SMOKE IN THE LAVATORY OR CABIN. SHE ADVISED ME THAT SHE SMELLED SMOKE AND ALSO THE LAVATORY SMOKE ALARM IN THE CABIN WAS ACTIVATED. I ADVISED THE FLT ATTENDANT THE EMER AT HAND AND INSTRUCTED HER TO PREPARE THE CABIN FOR POSSIBLE GND EVAC. I DECLARED AN EMER WITH DEP CTL AND REQUESTED TO RETURN TO ARPT WITH CFR STANDING BY. ON SHORT FINAL EICAS MASTER WARNING LAVATORY SMOKE ANNUNCIATION EXTINGUISHED; AT WHICH TIME I INQUIRED WITH THE FLT ATTENDANT IF SHE STILL SMELLED SMOKE. SHE DID NOT. A NORMAL APCH TO A LNDG WAS MADE. NO INDICATION OR EVIDENCE OF SMOKE REMAINED. WE TAXIED TO THE GATE WITH CFR UNITS ESCORTING US. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE FEEDBACK FROM MAINT WAS THE HEAT THAT TRIGGERED THE SMOKE ALARM WAS CAUSED BY THE LAVATORY CEILING LIGHT. THE LAVATORY WAS DEFERRED AS INOP PER THE MEL WHICH REQUIRES THE LAVATORY DOOR BE CLOSED AND LOCKED. WHEN THE DOOR IS CLOSED THE CEILING OVERHEAD LIGHT IS ILLUMINATED AND PER MAINT THIS CAUSED THE LAVATORY SMOKE ALARM AND EICAS WARNING TO ACTIVATE. THE RPTR STATED THE CABIN ATTENDANT RPTED SHE DID SMELL SMOKE WHEN THE LAVATORY SMOKE ALARM WAS ACTIVATED AND WHEN ASKED AGAIN ON FINAL APCH NO SMOKE WAS NOTICED.