Challenger 350
Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine; Flight Crew Instrument
Communication Breakdown; Troubleshooting; Distraction; Time Pressure
Aircraft Equipment Problem Critical; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Air Traffic Control Provided Assistance; Flight Crew Requested ATC Assistance / Clarification; General Evacuated; General Maintenance Action
Aircraft
Approximately 45 min prior to passengers arrival; we were scheduled to ground move. My SIC and I had offered to fly a trip on Aircraft X to ZZZ. We had more duty time than the current crew. Originally; Scheduling declined. Then; we received the trip. The aircraft was handed off to us. The previous crew had made all preparations for flight. Although; we were time compressed; all items in the Normal Procedures Checklist Power On and Cockpit Preparations sections were again completed. The PDC clearance was reviewed and accepted. Dual verification accomplished. Our passengers arrived before other flight deck briefings were started. Standard SOPs were followed to board passengers; load bags; etc. Each crew member accomplished a Final Walk-Around. With the main cabin and baggage compartment doors secured and both crew members on the flight deck; my SIC reviewed the ATIS and general flight deck set up. Next; I performed the required Crew; Departure and Takeoff Briefings per the Normal Procedures Checklist. We were taxiing from the Ramp to the Runway with two passengers aboard. Both engines and the APU were operating. The ECS was on the APU. On taxiway 'N' we crossed [an adjacent runway] and were instructed to switch to the Tower. My SIC made the frequency change and I called for the Before Takeoff Checklist. As that action was completed; an unusual odor became apparent. My SIC asked me if I smelled that. I replied yes. I directed my SIC to inform ATC that we needed to investigate an issue. The controller instructed us to turn onto taxiway 'N1'.I looked at the CB panel behind the copilot's seat and my SIC looked at the CB panel behind the Captain's seat. Nothing was amiss. Concurring; my SIC left the flight deck to check other circuit breaker panels; the galley; cabin; lavatory and baggage compartment. With his departure the fumes subsided. Unknown to me at the time; he was met by the lead passenger who also smelled the odor. Walking forward from the rear of the cabin my SIC saw a gray haze in the entire galley. With my head set on; I never heard my SIC reporting smoke in the cabin.The odor; much stronger than before; returned to the flight deck. In my right peripheral vision I saw a gray cloud. Simultaneously; I advised ATC to roll the equipment and informed them that we would be evacuating onto the taxiway; [with] four souls on board and 7 hours of fuel. Almost automatically; my First Officer (FO) secured AC and DC electrical power as he returned to the SIC seat. I called for the Evacuation QRC. We completed the checklist. I sent my SIC to open the main cabin door. I reviewed my QRF one last time. My FO led the passengers outside and I followed them. Fire Rescue arrived on scene. The unusual odor was still present inside and outside the aircraft (fire rescue; crew and passengers could smell it). At the direction of Fire Rescue; my SIC escorted their personnel through the cabin. Fire Rescue members and myself confirmed that our passengers were not in distress. Both indicated that they did not require medical attention. External access panels were opened for Fire Rescue but nothing unusual was discovered.The airport authority provided a vehicle and driver for our passengers. Accompanied by my SIC; our passengers and their bags were returned to the FBO. My SIC and the [company] managed their needs.With Fire Rescue in custody of Aircraft; I made a preliminary phone call to the [company]. My SIC returned from the FBO. Gear pins were inserted and the aircraft chocked.Eventually; Fire Rescue released Aircraft. All parties agreed that no power would be put on the aircraft. Aircraft was put under tow with appropriate escort and tugged to the ramp. There the emergency lights expired due to depleted batteries. The aircraft was secured and turned over to maintenance with a technician already on scene.  Appropriate entries were made in the aircraft log book. The evacuation went well. My SIC's performance was trulyoutstanding!!! I hardly had to direct him. The passengers; crew and aircraft are safe. We can always do better. As professionals these matters are reviewed to enhance safety and improve performance. When requesting the rescue equipment; I forgot that we were already on tower frequency and called them ground. I did not vocalize the Evacuation QRC with clarity. We missed shutting down the APU from the fire control panel... I used the rotating APU on/off/start switch instead. I observed my SIC place the QRH in the slot by his seat as he maneuvered toward the main cabin door. Only then did I realize that we had used the evacuation checklist from the QRH. Consequently; I reviewed the QRC items. These items were my responsibility and they are my errors alone. Even with the time compression; I felt that we were ready to fly.
Challenger 350 Captain reported electrical fumes in the aircraft during taxi for takeoff resulted in the passengers being deplaned on the taxiway.