Date: 202101
Local time of day: 1201-1800
Location: ZZZ.ARTCC, US
Flight conditions: IMC
Weather elements / visibility: 1
Light: Daylight
Aircraft: Gulfstream IV / G350 / G450
Operator: Corporate
Operating under: Part 135
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Air Conditioning and Pressurization Pack
Component problem: Malfunctioning
Reporter organization: Corporate
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Flight Instructor
Human factors: Troubleshooting; Workload
Anomaly: Aircraft Equipment Problem Critical; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor
Detector: Automation Aircraft Other Automation
When detected: In-flight
Result: Flight Crew Diverted; Flight Crew Landed in Emergency Condition
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: Our aircraft departed ZZZ at approximately XA:40Z on an IFR flight plan headed to ZZZ airport. Name was the pilot flying and I was the pilot monitoring. We climbed and cruised uneventfully at an initial altitude of FL430. After about 20 minutes at altitude; a passenger came to the flight deck and asked if we could cool down the cabin. As I set the cabin temperature controller to a cooler temperature. After about 5 minutes; the 'R COOL TURBINE HOT' CAS message came on. We performed the appropriate checklist and after a minute the CAS message went out.At this point; the cabin was at a hotter temperature than before and the passengers complained again. The PF decided to go back into the cabin to verify that all the gasper vents were open and to check if there were any other indications of potential issues. It was apparent that there was a significant temperature difference from the forward portion of the cabin compared to the aft. The forward cabin was at least 10 degrees warmer than the aft. Additionally; the PF noticed some warm air coming out of the vents. After checking the upper cabin gasper vents; the PF returned to his seat. After a short discussion on possible issues; we elected to descend to FL390.When the aircraft leveled at FL390; the Cabin Attendant came up to the flight deck and asked the PF if he noticed any haze in the cabin. The PF looked back and saw no smoke or haze. The Cabin Attendant went about her duties.After a few more minutes; the PF noticed smoke coming from my right-side vent and we received another 'R COOL TURBINE HOT' CAS message. The PF immediately donned his O2 mask and asked me to request an immediate descent and to pull out the checklist. At this time; the cabin started to fill up with visible smoke and the cabin attendant came up to the flight deck to respond. Now it has become our priority to get this airplane on the ground as soon and safely as possible. The cabin attendant donned her O2 mask. After O2 masks were on; the appropriate checklists were performed. The cabin started to depressurize immediately after the Right Pack was turned off (as required by the 'R COOL TURBINE HOT' checklist). I had to also switch the pressurization to manual and that increased my workload; as I had to control and visually monitor the opening of the safety valve. At this point; a rapid descent was performed. During the descent; smoke remained in the cabin. Due to the smoke in the cabin; a loss of pressurization; we requested for vectors to the nearest suitable airport which was ZZZ1. During the descent; the passenger O2 masks deployed; and the Cabin attendant instructed the passengers to put their O2 masks on. At about 15;000ft; the smoke started to dissipate. We continued our descent per ATC to 6;000 feet and continued with vectors for an ILS XX approach at ZZZ1. Now the cabin was completely clear of smoke. The crew took off their O2 masks and completed all remainder checklists for landing. The aircraft landed uneventfully on [Runway] XX.Upon the landing roll out; Fire and Rescue was approved on the runway to follow us to our parking spot on ramp. After shutting down engines and securing the aircraft; we assessed the situation and verified that all passengers were OK and there were no injuries.




Synopsis: Gulfstream IV Captain reported that the air conditioning system began malfunctioning and smoke filled the cabin; resulting in an immediate descent and diversion. During descent the smoke dissipated.