Gulfstream IV / G350 / G450
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 120; Flight Crew Total 5500; Flight Crew Type 1100
Aircraft Equipment Problem Critical
Air Traffic Control Issued New Clearance; Flight Crew Landed As Precaution; Flight Crew Took Evasive Action; Flight Crew Diverted; General Maintenance Action
Aircraft
The First Officer was the pilot flying. Prior to climbing through FL410 the First Officer donned his oxygen mask and was using supplemental oxygen. Approximately 20 minutes after departure at FL450 we received a CABIN PRESSURE LOW message on the crew alerting system. The Captain immediately donned his oxygen mask and started using supplemental oxygen and then took over the flight controls from the First Officer. We confirmed the validity of the message by looking at the increasingly high Cabin Altitude on the CABIN PRESSURE CONTROLLER and initiated a rapid emergency descent with engines at idle thrust and speed brakes deployed while monitoring for other aircraft visually and on TCAS.We [advised ATC] and requested a diversion to [a nearby alternate]. We completed the checklist and QRH items. We landed without further incident.Aircraft Maintenance discovered that the baggage door seal would not fully inflate; and led to cabin pressure loss.
[Report narrative contained no additional information.]
G-IV flight crew reported diverting to a nearby alternate after a malfunctioning cargo door seal led to a loss of cabin pressure.