Narrative:

Approximately 30 seconds after takeoff (I was PF) the master warning sounded and the captain read out loud 'smoke toilet' from the EICAS screen. He immediately said 'we're headin back' and I agreed. We continued through the (normal) after takeoff checklist; then notified ATC of our smoke indication and that we are declaring an emergency and would like to continue straight out. ATC gave us a heading and said they understood we wanted to come back to land in ZZZ and that they would have the trucks waiting for us on the runway. I then called for a descent checklist when able from the captain. The captain told me to take the radios while he made contact with the flight attendant. The flight attendant informed us that there was a loud horn coming from the rear of the cabin; but that she could neither smell nor see smoke coming from the lavatory. He informed her that we would be returning back to ZZZ and that if she noticed anything at all to call us and let us know in the flight deck. After receiving a downwind vector for runway 30L; the EICAS annunciation disappeared. We still ran through the descent checklist and then I called for the emergency checklist for smoke toilet. The checklist called for us to prepare to land immediately at the nearest suitable airport. Due to the lack of time available; and for all practical purposes; we continued with setting up the approach and running our normal checklists; instead of searching of the 5 circuit breakers that the checklist called for us to open. The landing was uneventful. We taxied off runway and switched to a frequency to talk with crash fire rescue equipment. They affirmed there were no abnormal heat readings coming from the tail of the aircraft. We decided to taxi back to the gate and have them follow us to deplane the passenger.

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Original NASA ASRS Text

Title: A CRJ-900 FLT CREW EXPERIENCED MASTER WARNING 'SMOKE TOILET' SHORTLY AFTER TAKEOFF. THEY DECLARED AN EMERGENCY AND RETURNED TO LAND AT THE DEPARTURE AIRPORT.

Narrative: APPROX 30 SECONDS AFTER TKOF (I WAS PF) THE MASTER WARNING SOUNDED AND THE CAPT READ OUT LOUD 'SMOKE TOILET' FROM THE EICAS SCREEN. HE IMMEDIATELY SAID 'WE'RE HEADIN BACK' AND I AGREED. WE CONTINUED THROUGH THE (NORMAL) AFTER TKOF CHKLIST; THEN NOTIFIED ATC OF OUR SMOKE INDICATION AND THAT WE ARE DECLARING AN EMER AND WOULD LIKE TO CONTINUE STRAIGHT OUT. ATC GAVE US A HDG AND SAID THEY UNDERSTOOD WE WANTED TO COME BACK TO LAND IN ZZZ AND THAT THEY WOULD HAVE THE TRUCKS WAITING FOR US ON THE RWY. I THEN CALLED FOR A DSCNT CHKLIST WHEN ABLE FROM THE CAPT. THE CAPT TOLD ME TO TAKE THE RADIOS WHILE HE MADE CONTACT WITH THE FLT ATTENDANT. THE FLT ATTENDANT INFORMED US THAT THERE WAS A LOUD HORN COMING FROM THE REAR OF THE CABIN; BUT THAT SHE COULD NEITHER SMELL NOR SEE SMOKE COMING FROM THE LAVATORY. HE INFORMED HER THAT WE WOULD BE RETURNING BACK TO ZZZ AND THAT IF SHE NOTICED ANYTHING AT ALL TO CALL US AND LET US KNOW IN THE FLT DECK. AFTER RECEIVING A DOWNWIND VECTOR FOR RWY 30L; THE EICAS ANNUNCIATION DISAPPEARED. WE STILL RAN THROUGH THE DSCNT CHKLIST AND THEN I CALLED FOR THE EMER CHKLIST FOR SMOKE TOILET. THE CHKLIST CALLED FOR US TO PREPARE TO LAND IMMEDIATELY AT THE NEAREST SUITABLE ARPT. DUE TO THE LACK OF TIME AVAILABLE; AND FOR ALL PRACTICAL PURPOSES; WE CONTINUED WITH SETTING UP THE APCH AND RUNNING OUR NORMAL CHKLISTS; INSTEAD OF SEARCHING OF THE 5 CIRCUIT BREAKERS THAT THE CHKLIST CALLED FOR US TO OPEN. THE LNDG WAS UNEVENTFUL. WE TAXIED OFF RWY AND SWITCHED TO A FREQ TO TALK WITH CFR. THEY AFFIRMED THERE WERE NO ABNORMAL HEAT READINGS COMING FROM THE TAIL OF THE ACFT. WE DECIDED TO TAXI BACK TO THE GATE AND HAVE THEM FOLLOW US TO DEPLANE THE PAX.

Data retrieved from NASA's ASRS site as of May 2009 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.