Date: 201212
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Daylight
Aircraft: EMB ERJ 170/175 ER/LR
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Takeoff / Launch
Airspace: Class C ZZZ
ATC / advisory: Tower ZZZ
Reporter organization: Air Carrier
Reporter function: Pilot Flying; First Officer
Human factors: Confusion; Situational Awareness; Physiological - Other; Distraction
Second reporter function: Flight Attendant (On Duty)
Anomaly: Aircraft Equipment Problem Critical; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Detector: Automation Aircraft Other Automation; Person Flight Crew; Person Flight Attendant
When detected: In-flight
Result: Flight Crew Returned To Departure Airport; Flight Crew Landed in Emergency Condition; General Declared Emergency
Contributing factors: Aircraft; Human Factors; Procedure
Primary problem: Procedure

Narrative: After applying takeoff thrust both pilots smelled a strange odor in the flight deck. After rotation; at approximately 1;000 MSL; the odor significantly increased and as we were discussing what actions we should take a LAV SMOKE indication came up on the EICAS. We exchanged flight controls; donned the oxygen masks; declared an emergency with ATC; advised them about the situation and told them that we were returning for landing.I answered an emergency call from the cabin crew and told them about the indication that we have and asked them if there was any visible smoke coming out of the lavatories. The two flight attendants told me that there was some haze in the cabin; not really smoke but a very strong odor. I advised them that we had declared an emergency with ATC and were returning to the airport for landing. The Captain was on downwind abeam the numbers and we started configuring the airplane for landing. After touchdown; as we cleared the runway; the odor was significantly lower and the LAV SMOKE indication had disappeared. I contacted the flight attendants to see what the situation was in the cabin so we could make a decision regarding the need to evacuate. They told me that the odor was not as bad and there was no smoke coming out of the lavatories so we decided to return to the gate. Once we arrived at the gate CFR personnel came in and inspected the lavatory.


Second narrative: Upon boarding the aircraft; we were notified via a letter from Maintenance that the engines had been cleaned the night before and that we and/or the passengers might notice an unusual odor once the engines were started. My flying partner and I had both experienced this before; so we knew what to expect. As soon as we started taxiing under our own power; we started to notice a strong odor in the cabin. The smell got progressively stronger as our ground speed increased. The odor was very strong right after takeoff. I assured the passengers immediately in front of my jumpseat that this was not unusual; due to the engine cleaning that had recently taken place. Very shortly after takeoff there was an audible and visual indication from the front lavatory smoke detector. I immediately called my partner in the back and asked him if this was due to the residue from the engine cleaning. He thought it most likely was. I then called the flight deck; using the emergency button; to confirm my suspicions. I was told that they were aware of the alarm and that we would be returning to the gate. I made an announcement to the passengers that we would be returning to the gate and to ensure their seatbelts were fastened. I believe I also told them at this time that there was NOT a fire on board the aircraft and that we would hear from the Captain as soon as he was free from other responsibilities. During our descent and before landing; the alarm stopped chiming. Upon landing; I asked the passengers to remain in their seats. I told them we didn't know at that time if we would be deplaning and to stand by for word from the Captain. While taxiing in; the First Officer reiterated that the alarm had ceased and he asked if the air was clear. My colleague and I informed him that the air had cleared somewhat; but some haze was still visible in the cabin. The Captain then asked if we needed to deplane the passengers immediately; or if we could return to the gate. Since there appeared no immediate risk or danger; I advised that we could return to the gate. We returned to the gate and the passengers deplaned into the terminal in an orderly fashion. All passengers appeared calm and no injuries were reported.


Synopsis: Despite a forewarning from Maintenance regarding the possibility of residual air conditioning odors due to cleaning of the engines the previous night; the flight crew of an ERJ-170 elected to return to their departure airport after takeoff due to the level of contamination and the fact that the associated haze had appeared to trigger a lavatory smoke alarm.