Gulfstream G200 (IAI 1126 Galaxy)
Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Critical
Flight Crew Returned To Departure Airport
Aircraft
[After departure]; upon retraction of the landing gear the amber message 'cabin door' came on. I was the pilot flying. At safe altitude and autopilot engaged I called for the checklist and took over the radio. After asking to level off at 5;000 ft; we noticed that the cabin rate matched the rate of climb of the airplane; which prompted me to shallow out the climb. We agreed that the safest course of action was to return to [departure airport]. I asked for delay vectors; as we were about 600 lbs overweight; and 3;000 ft with probable return to the field. The First Officer briefed the [passengers] on the dynamics of the situation. After transferring controls; I called the [Chief Pilot] on duty and described the predicament. He agreed on the plan of action and started the recovery process. I then called [FBO] to alert them of our arrival. Upon reaching max landing weight we were turned to final on a visual. Landing was uneventful although the ground air brakes did not deploy. We assisted the [passengers] until the recovery crew came from the hotel. They never showed any concern and were very polite in the interaction with us and the next crew.
G-200 fractional Captain reported noting after takeoff they got a 'CABIN DOOR' warning and the aircraft did not pressurize. Flight returned to departure airport.