Gulfstream IV / G350 / G450
Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Clearance; Flight Deck / Cabin / Aircraft Event Other / Unknown
Flight Crew Diverted; Flight Crew Landed in Emergency Condition
Aircraft
While flying from ZZZZ to ZZZ; we experienced a loss of pressurization about one and a half hours into the flight. We first heard a loud squeal by the main cabin door and then saw that the cabin altitude was beginning to rise uncontrollably. We [requested priority handling] and started an emergency descent to 15;000 ft. We followed the emergency descent and loss of pressurization checklist in the QRH. We calculated our range and contacted company; and formulated the plan to divert to ZZZ1. We landed in ZZZ1 about 2 hours later without any other events.
GIV-SP Captain reported a loss of cabin pressurization during cruise and diverted uneventfully.