Narrative:

In ZZZ after maintenance checked out the lavatory smoke sensor; we elected to perform a full power run-up of both engines to see if we could set off the lavatory smoke indication. Doing the run-up with maintenance on board and in contact with maintenance control we did not get the lavatory smoke indication. In discussion with maintenance control and maintenance on board we concluded it was an issue with the sensor and it was taken care of. So maintenance control released the aircraft and we decided to board. After takeoff on runway 23L around 1500 ft AGL we received a lavatory smoke indication on the EICAS. The first officer and I performed the memory items for lavatory smoke; declared an emergency and was vectored onto downwind for runway at ZZZ as briefed. We then talked to the flight attendant and she confirmed that there was visible smoke and a strong odor in the forward cabin compartment. In the cockpit there was no visible smoke or odor. We then told the flight attendant that we would be evacing on the runway. Landed on runway 23R and proceeded with the evacuate/evacuation procedures. Evacuate/evacuation was executed without incident. Callback conversation with reporter revealed the following information: reporter stated prior to his flight; even though maintenance checked out the lav smoke detector and both he and the co-pilot had performed full power run-ups with both engines; they could not duplicate the earlier lav smoke detector indication. However; after the in-flight incident of visible smoke; strong odor; emergency declared and return to field; maintenance took the plane out of service. Engine runs were performed again; but this time maintenance isolated the engine bleeds to the air conditioning packs to see if they could determine if one of the engines was contributing to the visible smoke that appeared in the cabin after takeoff. As a result; #1 engine was found to be leaking oil from the engine oil tank due to a failed oil seal. The resultant smoke was drawn into the engine through the bleeds into the cabin air conditioning pack. These are rolls royce allison engines. This aircraft has only one lav in the aft end of the cabin.

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Original NASA ASRS Text

Title: AFTER TKOF AND APPROX 1500 AGL; AN EMB-145LR (ERJ-145LR) FLIGHT CREW RECEIVED A 'LAV SMOKE' INDICATION ON THEIR EICAS DISPLAY. EMERGENCY DECLARED; ACFT LANDED AND PASSENGERS EVACUATED.

Narrative: IN ZZZ AFTER MAINT CHKED OUT THE LAVATORY SMOKE SENSOR; WE ELECTED TO PERFORM A FULL PWR RUN-UP OF BOTH ENGS TO SEE IF WE COULD SET OFF THE LAVATORY SMOKE INDICATION. DOING THE RUN-UP WITH MAINT ON BOARD AND IN CONTACT WITH MAINT CTL WE DID NOT GET THE LAVATORY SMOKE INDICATION. IN DISCUSSION WITH MAINT CTL AND MAINT ON BOARD WE CONCLUDED IT WAS AN ISSUE WITH THE SENSOR AND IT WAS TAKEN CARE OF. SO MAINT CTL RELEASED THE ACFT AND WE DECIDED TO BOARD. AFTER TKOF ON RWY 23L AROUND 1500 FT AGL WE RECEIVED A LAVATORY SMOKE INDICATION ON THE EICAS. THE FO AND I PERFORMED THE MEMORY ITEMS FOR LAVATORY SMOKE; DECLARED AN EMER AND WAS VECTORED ONTO DOWNWIND FOR RWY AT ZZZ AS BRIEFED. WE THEN TALKED TO THE FLT ATTENDANT AND SHE CONFIRMED THAT THERE WAS VISIBLE SMOKE AND A STRONG ODOR IN THE FORWARD CABIN COMPARTMENT. IN THE COCKPIT THERE WAS NO VISIBLE SMOKE OR ODOR. WE THEN TOLD THE FLT ATTENDANT THAT WE WOULD BE EVACING ON THE RWY. LANDED ON RWY 23R AND PROCEEDED WITH THE EVAC PROCS. EVAC WAS EXECUTED WITHOUT INCIDENT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: REPORTER STATED PRIOR TO HIS FLIGHT; EVEN THOUGH MAINT CHECKED OUT THE LAV SMOKE DETECTOR AND BOTH HE AND THE CO-PILOT HAD PERFORMED FULL POWER RUN-UPS WITH BOTH ENGINES; THEY COULD NOT DUPLICATE THE EARLIER LAV SMOKE DETECTOR INDICATION. HOWEVER; AFTER THE IN-FLIGHT INCIDENT OF VISIBLE SMOKE; STRONG ODOR; EMERGENCY DECLARED AND RETURN TO FIELD; MAINT TOOK THE PLANE OUT OF SERVICE. ENGINE RUNS WERE PERFORMED AGAIN; BUT THIS TIME MAINT ISOLATED THE ENG BLEEDS TO THE AIR CONDITIONING PACKS TO SEE IF THEY COULD DETERMINE IF ONE OF THE ENGINES WAS CONTRIBUTING TO THE VISIBLE SMOKE THAT APPEARED IN THE CABIN AFTER TKOF. AS A RESULT; #1 ENG WAS FOUND TO BE LEAKING OIL FROM THE ENG OIL TANK DUE TO A FAILED OIL SEAL. THE RESULTANT SMOKE WAS DRAWN INTO THE ENGINE THROUGH THE BLEEDS INTO THE CABIN AIR CONDITIONING PACK. THESE ARE ROLLS ROYCE ALLISON ENGINES. THIS ACFT HAS ONLY ONE LAV IN THE AFT END OF THE CABIN.

Data retrieved from NASA's ASRS site as of January 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.