CRJ-900 RETURNED TO DEPARTURE AIRPORT DUE TO A LAVATORY SMOKE ALARM.

Narrative

UPON INITIAL TAKEOFF THRUST APPLICATION; BOTH THE FIRST OFFICER AND I NOTED A BRIEF ODOR WHICH THEN PROMPTLY DISSIPATED. OTHER THAN THE ODOR; THE TAKEOFF ROLL AND ROTATION WERE NORMAL. THE AFTER TAKEOFF CHECKLIST WAS COMPLETED. UPON INITIAL CLIMBOUT A 'SMOKE TOILET' EICAS CAUTION MESSAGE ILLUMINATED. I DIRECTED THE FIRST OFFICER TO CALL THE FLIGHT ATTENDANT TO CONFIRM IF THERE WERE ANY SIGNS OF SMOKE OR FIRE IN THE LAVATORY AND TO ALSO COMPLETE THE 'SMOKE TOILET' NON-NORMAL CHECKLIST IN THE OPERATIONS MANUAL. WHILE THE FIRST OFFICER WAS COMMUNICATING WITH THE FLIGHT ATTENDANT; I INFORMED DEPARTURE THAT WE WOULD LIKE VECTORS TO REMAIN IN THE TERMINAL AREA OF THE AIRPORT FOR A POSSIBLE ISSUE CONCERNING SMOKE IN THE LAVATORY. THE FLIGHT ATTENDANT REPORTED THAT THE LAVATORY SMOKE ALARM WAS SOUNDING. HOWEVER; SHE REPORTED THAT THERE WERE NO INDICATIONS OF SMOKE OR FIRE. I THEN INSTRUCTED THE FIRST OFFICER TO ASSUME CONTROL OF THE AIRCRAFT AND COMMUNICATION 1 RADIOS AND I WOULD ASSUME PILOT NOT FLYING DUTIES. I THEN CONTACTED OUR MAINTENANCE AND DISPATCH DEPARTMENTS OVER COMPANY RADIO TO DISCUSS THE SITUATION. WHILE COMMUNICATING WITH THESE 2 DEPARTMENTS; THE 'SMOKE TOILET' CAUTION MESSAGE EXTINGUISHED FROM THE EICAS DISPLAY SYSTEM. IN MY ESTIMATION; THE 'SMOKE TOILET' CAUTION MESSAGE WAS ILLUMINATED FOR APPROXIMATELY 5 MINUTES. I CONTACTED THE FLIGHT ATTENDANT AGAIN TO CONFIRM THAT THERE WAS STILL NO SIGN OF SMOKE OR FIRE; AND SHE POSITIVELY CONFIRMED THERE WERE NO SIGNS OF SMOKE OR FIRE IN THE LAVATORY. AT THIS POINT I WAS STILL IN COMMUNICATION WITH DISPATCH AND MAINTENANCE AND TOLD THEM THAT THE CAUTION MESSAGE CONCERNING LAVATORY SMOKE HAD NOW EXTINGUISHED AND THAT THE FLIGHT ATTENDANT CONTINUED TO REPORT NO SIGNS OF SMOKE OR FIRE IN THE LAVATORY. AS WE WERE DISCUSSING THE CONTINUATION OF OUR FLIGHT; THE FLIGHT ATTENDANT THEN CONTACTED THE FLIGHT DECK AND REPORTED THAT; ALONG WITH OTHER PASSENGERS; SHE SMELLED A 'FOUL' ODOR IN THE CABIN. AT THIS TIME I DIRECTED THE FIRST OFFICER TO DECLARE AN EMERGENCY WITH APPROACH AND REQUEST VECTORS TO RUNWAY 22R. I ADVISED THE FLIGHT ATTENDANT THAT WE WERE DECLARING AN EMERGENCY; AND WE WOULD BE ON THE GROUND IN APPROXIMATELY 10 MINUTES OR LESS. I ALSO ASKED HER TO KEEP US ADVISED OF ANY CHANGES IN THE CABIN AND LAVATORY. ADDITIONALLY; I MADE A PA ANNOUNCEMENT TO THE PASSENGERS ADVISING THEM OF THE SITUATION. WE COMPLETED THE CRUISE; DESCENT; APPROACH; AND FINAL CHECKLISTS NORMALLY. THE FIRST OFFICER MADE A NORMAL LANDING. AFTER EXITING THE RUNWAY; I DIRECTED THE FIRST OFFICER TO CONTACT THE FLIGHT ATTENDANT TO ADVISE HER AND THE PASSENGERS TO STAND BY. I THEN CONTACTED CFR DIRECTLY ON GROUND FREQUENCY. I DIRECTED CFR TO CIRCLE THE AIRCRAFT AND CHECK FOR ANY INDICATIONS OF SMOKE OR FIRE. CFR REPORTED THAT THERE WERE NO SIGNS OF SMOKE OR FIRE. WE THEN TAXIED BACK TO GATE UNEVENTFULLY.