Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP)
Training / Qualification; Troubleshooting; Confusion
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural FAR; Deviation / Discrepancy - Procedural Maintenance; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Returned To Departure Airport; General Flight Cancelled / Delayed; General Maintenance Action
Procedure; Human Factors; Incorrect / Not Installed / Unavailable Part; Aircraft
We departed for an empty reposition leg from ZZZ - ZZZ1. Climbing through approximately 10;000 feet we began to experience compounding failures. First; our 60 Hz Converter failed; our left and right packs turned off; [and] our cabin pressure controller defaulted to manual control and would not reset back to auto. Our cabin began to climb excessively; cabin pressure low illuminated; cabin oxygen on - I immediately initiated a turnaround back to ZZZ and began a descent. We advised ATC and landed back at ZZZ. After several days of maintenance; it was discovered that the Mechanic assigned to fix our aircraft installed an unapproved E-INVERTER which was not listed in the IPC (Illustrated Parts Catalog) for a GIV and did not properly secure a cannon plug. These issues were later fixed by the Gulfstream FAST.From a pilot perspective this was unavoidable. The errors that occurred here are solely on the maintenance side. The IPC should have been consulted prior to ordering and installing any part on any aircraft. This did not happen.
GIV Captain reported an air turnback after multiple electrical failures that were caused by a Mechanic installing an unapproved inverter in the aircraft.