Date: 201707
Local time of day: 1201-1800
Location: ZZZZ.Airport, FO
Flight conditions: VMC
Light: Daylight
Aircraft: Citation X (C750)
Operator: Air Taxi
Operating under: Part 135
Flight plan: IFR
Mission: Ferry / Re-Positioning
Flight phase: Cruise
ATC / advisory: Center ZZZZ
Aircraft component: Hydraulic Main System
Component problem: Malfunctioning
Reporter organization: Air Taxi
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Workload; Troubleshooting; Situational Awareness
Second reporter function: Pilot Flying; First Officer
Anomaly: Aircraft Equipment Problem Less Severe; Inflight Event / Encounter Other / Unknown
Detector: Automation Aircraft Other Automation; Person Flight Crew
When detected: In-flight
Result: Flight Crew Diverted; Flight Crew Landed in Emergency Condition; General Maintenance Action
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: At 45;000 feet; the First Officer and I got a HYD quantity low A AMBR CAS message at 16%. The First Office was flying this leg. Immediately; I pulled the HDY/B PTU (Power Transfer Unit) circuit breaker to salvage what was left on the A reservoir. I was in the left seat and the PNF and the First Officer was the PF in the right seat. At this time; we transferred controls to me and the First Officer conducted the checklist items in the QRH. In the meantime; we discussed options where to land since we were crippled with the A system. I transferred controls back to the First Officer and called Maintenance Control. After speaking with them; Maintenance brought all parties up to speed on our situation. ATC allowed us to stay high to save fuel. The First Officer did an amazing job communicating with ATC; Maintenance Control; and working through the QRH. After going back and forth with Maintenance Control on where to land; we decided on a bottom line in terms of minimum fuel and decided on a maximum cross wind component of no more than 10 knots. ZZZ had the longest and most suitable winds for landing based on the D-ATIS. Dispatch coordinated with ATC our plan and told Maintenance Control we will be diverting. We declined to land at ZZZ1 for several reasons. The primary reason was the wind at the time that we checked it was at; or close to; our operational limit. That considered; the additional 20 minutes of flying time to an uncertain aerodrome was agreed not to be prudent. The other options we considered were two airports fairly close to one another. We chose our final destination; again; for several reasons over the options. The first reason was available runway length. Due to the fact that neither of us are test pilots and our stress level was high we wanted to have the absolute most runway possible despite having ample runway considering unfactored distances from the QRH. ZZZ2's runway after the displaced threshold and glideslope had less than 7;500 ft. The winds were also not favorable at the time we checked.Runway XX was selected for the following reasons: 1. It was longest runway of all available in the region with a landing distance available greater than 11;000 ft.2. The winds were favorable.3. ZZZ had better crash and fire services (E in ZZZ over D in ZZZ2). 4. It was the closest runway to us. The closeness of the runway was not a factor as far as 'emergency time' or that we thought we needed to land quickly. The benefit of having the closest runway was having conserved fuel in enroute burn.We worked together as a crew and split the tasks that needed to be done prior to beginning the descent into ZZZ. We briefed the approach; our contingencies and back up plans in the event we had to go missed. After getting the current winds on final; we monitored the wind vector on the EICAS screen as we were on final. Our bottom line for winds was 9 knots. On final; I was paying attention to drift while the First Officer was calling out deviations. Following the QRH on the descent; we blew the main landing gear down; limited our flaps to 15 and landed with emergency brakes. We landed safely and stopped on the runway without incident and had fire/crash trucks; airport authority and the FBO greet us. There was 4;000 ft of runway remaining. ZZZ airport fire rescue assessed the temperature on the brakes and determined they were initially too hot to approach. After about ten minutes; the aircraft was cleared by the fire captain to be towed off the runway. The FBO towed us to Customs and then to the FBO.The PTU circuit breaker is not a memory item. But it requires action more immediately than QRH procedures allow. I suggest making an official; documented procedure around the pulling of this breaker. Good piloting; experience and tribal knowledge is the current method.


Second narrative: [Report narrative contained no additional information.]


Synopsis: CE-750 flight crew reported diverting on an international return flight after the aircraft hydraulic system began leaking. The flight landed without incident.