Citation X (C750)
Flight Crew Air Transport Pilot (ATP)
Communication Breakdown
Conflict Ground Conflict; Critical
Flight Crew Became Reoriented; Flight Crew Took Evasive Action
Human Factors
We flew to CYUL and dropped passengers at the FBO. Weather was clear; greater than 5000/5. We kept the APU running and completed a quick turn and prepared to depart empty. We closed the door and completed the remainder of our preflight items including a final call to customs and a review of the flight plan by both pilots; followed by the before Start Checklist. As soon as the door was closed; a lineman was positioned and ready for engine start and taxi; it took us about 10 more minutes to complete our preflight checks once we closed the door. We were in no rush whatsoever and had plenty of time to be thorough. Engine start was uneventful and we prepared to taxi by calling ground. Ground Control gave us taxi instructions and stated a helicopter was inbound to the General Aviation ramp and would remain east of R taxiway. The 'General Aviation ramp' on the airport diagram includes many FBO's; ramps; and hangars spaces all east of 23L and both pilots agreed to look out for him; although both pilots thought it was unlikely he was coming into our ramp since Ground Control did not tell us to hold our position and also since there was no empty ramp space where he could land. We were parked in the north corner of the ramp facing southwest; our plane parallel to runway 23L. After reviewing taxi instructions we signaled the lineman with the taxi light that we were ready to taxi. He was extremely professional in his taxi signals and directed us to taxi forward and then begin turning to the right. We did this slowly and carefully and as I was transitioning my sight from the Lineman who was now at my 10 o'clock position to the threshold of the Uncontrolled General Aviation Ramp at my 2 o'clock position; the SIC called out 'stop; stop'. I applied the brakes and asked what was wrong because I could not see any hazards. She pointed up out of the right cockpit side windshield. I leaned in and saw the skids of a helicopter in a flare position. The helicopter seemed to be approaching to land and aiming for our marshaller; but saw us at the last minute and climbed back up and saw the other marshaller about 100 feet southwest of us directing him to land facing northeast (facing the other direction/towards us). The SIC stated she saw the non-flying/right-seat pilot in the helicopter urgently pointing at us to the left-seat pilot who somehow didn't see us though we were in his window. When he finally saw us; the helicopter flared and went over our aircraft. We determined later that the helicopter came around the corner of the large hangars from our 5 o'clock high position so was completely in our blind spot. Only when we started our slow right turn and he came into our 3 o'clock high position is when he became visible to the right-seat pilot. Basically he was paralleling our slow track but behind us in our blind spot. The SIC immediately called Ground and stated what had just happened. Ground stated the GA ramp is uncontrolled; which we had seen on the airport diagram. We taxied clear of the GA ramp and then asked Ground if we could hold our position. The SIC called the FBO on the radio and advised what had just occurred. The FBO staff summoned the FBO manager who immediately responded; apologizing profusely and stated he had just spoken to the PIC of helicopter. The helicopter PIC stated he was at fault; that they were actually supposed to come in over the taxiway but didn't; that he had a bad approach into the GA ramp and became fixated on the marshaller; who was in actuality our marshaller and not his; his was on the other side of the ramp. We queried the manager as to why the lineman did not signal us to stop if he could see the helicopter behind us. He stated that the helicopter had not called the FBO to warn them that it was inbound to their ramp so they were not looking for him; also that the incident happened so quickly and he came around the hangars from behind us; so there was no time for the marshaller to give us a signal and thatit was just a few seconds from when the helicopter appeared to when the incident occurred.  There was never any contact or damage of any sort. We also used our time stopped on the taxiway to give the chief pilot a call to talk about what just happened and determined we were fine to continue the trip back.Contributing to this scenario was the fact that the GA ramp was fairly crowded with aircraft and there was no wide open area away from us for the helicopter to land. This incident highlights the need to always keep your eyes scanning on a ramp or taxiway; even more so if the area is considered Uncontrolled as is the GA ramp at CYUL. Next time in a similar situation; we will query to what part of the GA ramp traffic is inbound and from what direction they are approaching; If it is not readily clear; we will stop and wait until certain there is no possible conflict. It is important to use marshallers and wing-walkers as good resources since they are able to see much of our plane and the ramp that we cannot. However; they cannot see everything and we need to continue to be diligent and watch out for hazards.
Report narrative contained no additional information.
CE750 flight crew describes a near collision with an air taxiing helicopter during taxi out of the FBO ramp under the direction of a Marshall. The helicopter had come around a hanger from behind the CE750 and had thought the CE750's Marshall was directing them.