Date: 202101
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Light: Daylight
Aircraft: Regional Jet 900 (CRJ900)
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Taxi
ATC / advisory: Tower ZZZ
Aircraft component: Air Conditioning and Pressurization Pack
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Human factors: Situational Awareness
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Detector: Person Flight Attendant; Person Flight Crew
When detected: Taxi
Result: Air Traffic Control Provided Assistance; Aircraft Equipment Problem Dissipated; Flight Crew Returned To Gate; Flight Crew Requested ATC Assistance / Clarification; General Flight Cancelled / Delayed; General Maintenance Action
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: While in line for takeoff on Taxiway for XXR; we received a notification from the flight attendants that the cabin was filling up with smoke which was coupled with a foul odor akin to burning rubber. We smelled the odor at the same time the flight attendants notified us of the smoke. I asked them if it was thick enough to block view of the back of the aircraft and if they thought we needed to evacuate right away. They answered no to both questions. I then told them that we would be moving to a cargo ramp to run a QRH and if they thought at any point we would need to evacuate while moving to call me back and we would stop immediately. I also informed them that the next time we stopped would be the last time we would move without calling them and that once stopped; if they felt the need to evacuate; they were to do it. We taxied to the cargo ramp just south of taxiway after alerting ATC that we were [requesting priority handling] and would be pulling off to the side to run a QRH and to have the fire trucks standby. We ran the entirety of the smoke fire fumes QRH; which had us deactivate the PACs (Air Conditioning Packs) and close the bleed valves. We elected to not drop pass O2 or go on O2 ourselves as we were not having any adverse reactions; but just dealing with an unpleasant smell in the flight deck. We called the flight attendants at this time and asked about the passengers' condition and they stated that everyone was fine. The smoke slowly dissipated throughout the rest of the event. At this point; we decided to go back to the gate as the smoke was no longer producing from the vents and the passengers were not complaining about any issues when asked. We cancelled [priority handling] but requested that crash rescue follow us to the gate. Once arriving at the gate with the aircraft shut down and the flight deck door open and main cabin door; we had one woman reportedly having bronchitis coughing to a large extent. She was the first off. I was not aware she had an adverse reaction until pulling into the gate. We deplaned everyone as quickly as possible and had Maintenance confirm that PAC 2 was the culprit. To my knowledge; all passengers refused medical attention. We later got another aircraft and had all passengers board.The probable cause was something happened with the Right PAC as we were single engine no APU taxiing to XXR with Engine 2 running.




Synopsis: CRJ-900 Captain reported a fumes event during taxi-out resulting in a return to the gate.