Small Transport; Low Wing; 2 Turbojet Eng
Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Other / Unknown
Deviation / Discrepancy - Procedural Published Material / Policy; Ground Event / Encounter Other / Unknown
General None Reported / Taken
Airport; Procedure; Human Factors; Equipment / Tooling; Environment - Non Weather Related
We blocked in on the ramp in ZZZ at (time). We shut down according to our AOM procedure. I kept the parking brake set; knowing we were not chocked. After seeing the passenger off and cleaning and postflighting the plane; we still [were] not chocked. I asked the FBO agent if she could get us some chocks since none were available on the new ramp they were using. The sedan that was to drive us to ZZZ1 showed up at the plane. We loaded our bags into the sedan. Still waiting for chocks and not wanting to leave the plane unchocked; I asked the sedan driver if he could drive us to the FBO about 200 yards away so I could get the chocks myself. When we got to the FBO; the FBO agent was leaving the FBO with chocks in hand. I spoke to the crew that was taking our plane to brief them of its status and fuel load. I happened to look out at the plane only to see it slowly rolling across the ramp. Two pilots from [FBO] were attempting to stop it. The sedan driver quickly drove us back to the plane. By this time the chocks were placed on the nose wheel. One of the [FBO] crew members said he had injured his right calf in attempting to physically stop the plane. I contacted the Company and spoke to the [Chief Pilot]. When back on the plane; [name] and I both noticed that the parking brake was still set. While chocked; we started the plane; checked the brakes and taxied to another part of the ramp. I set the parking brake again and brought the left engine up to about 60%. The brakes held. We shut down the plane. By this time the crew from [FBO] had departed the airport in their plane. I briefed the crew who were taking 583 of the situation; and they assumed control of the airplane for their trip to ZZZ2. I understand the ramp we parked on was recently opened but yet there were no chocks immediately available. Chocks should be located anywhere planes are expected to park. Also; would it be possible to have airplanes carrier their own set of chocks for instances like this?
Small Transport Jet Captain reported aircraft began to roll from parking position even though parking brake was set. Captain reported FBO had not yet inserted wheel chocks.