Date: 201909
Local time of day: 1201-1800
Location: ZZZ.ARTCC, US
Flight conditions: VMC
Light: Daylight
Aircraft: Regional Jet 900 (CRJ900)
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
ATC / advisory: Center ZZZ
Reporter organization: Air Carrier
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Human factors: Situational Awareness
Anomaly: Aircraft Equipment Problem Critical; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Detector: Person Flight Crew; Person Flight Attendant
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew Diverted; Flight Crew Landed in Emergency Condition; General Evacuated
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: During flight at FL350 we received a master warning for smoke aft lav. I transferred controls to my First Officer and then proceeded to call the flight attendants asking them to check for smoke. They said there was no smoke; and the message extinguished. Moments later it came back on and we ran the full QRH procedure. We diverted to ZZZ. As we were descending and the QRH was completed we got a call from the flight attendants that the cabin was filling with smoke. We both donned our oxygen masks and then I told the FAs that when we land there is a potential for deplaning and to 'assess and wait for my command.' I then [notified ATC] and continued towards our diversion airport of ZZZ. The descent check was not completed as policy states and I asked the First Officer to just do it himself so I could focus on getting us to the airport as fast as possible; as we had a possible fire in the back of the aircraft. I deviated from the 250 knots below 10;000 feet to get the airplane on the ground quickly due to the nature of the situation. We came in visually for Runway XL and had a normal landing. I used brakes and reverser to stop on the runway and then turned the aircraft right ten degrees to face into the wind. As I set the parking brake and called for the deplaning/expedited deplaning QRC; I heard; saw; and confirmed on the EICAS that the main cabin door was opened and that deplaning had been initiated by the FAs. I told Tower immediately that we were deplaning as there was several fire trucks approaching. The FO [First Officer] read the QRC and I accidentally took a few of his actions as he read them. For example the EMER DEPRESS button.  This did not affect the outcome or timing of the deplaning. We completed the [checklist] in its entirety then followed our protocols when deplaning.  I was the last one off the aircraft and ensured everyone was off. Once off; grabbed the passenger count; iPad for the aircraft logbook; and a cell phone to contact company.  Once off the aircraft I performed a head count and ensured no one was injured along with the first responders. Followed all protocols for notifying the company.  During deplaning all doors were opened including the over wing exits.  No injuries and everyone was accounted for. Smoke in the aft cabin caused the FAs to initiate deplaning along with a smoke aft lav master caution.  Just aircraft Maintenance; however; things happen sometimes and we just deal with it when it happens.




Synopsis: CRJ-900 Captain reported a diversion due to 'cabin filling with smoke.'