Date: 201511
Local time of day: 1801-2400
Location: ZZZ.Airport, US
Flight conditions: Mixed
Light: Night
Aircraft: Citation X (C750)
Operator: Corporate
Operating under: Part 91
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Hydraulic Main System
Component problem: Malfunctioning
Reporter organization: Corporate
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Flight Instructor; Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP)
Human factors: Fatigue; Situational Awareness
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Automation Aircraft Other Automation; Person Flight Crew
When detected: In-flight
Result: Flight Crew Landed in Emergency Condition; Flight Crew Diverted; General Maintenance Action
Contributing factors: Aircraft; Human Factors; Weather
Primary problem: Aircraft

Narrative: Several minutes into cruise flight; we received the CAS message 'HYD VOLUME LOW A' with the Master Caution light. I called for the Master Caution-Amber Message checklist; acknowledged the light; and brought up the Fuel/Hydraulic system synoptic page on the EICAS. Step one on the checklist is to check the hydraulic pressure and fluid quantity. Pressure appeared normal; but the quantity was holding steady at 17%; and temperature appeared normal. At top of cruise; a few minutes before; the A system quantity was checked per normal operations checklist and read better than 60%. Given that there was no abnormal temperature; nor fluctuations in pressure; I elected to wait and monitor before continuing with the Master Caution checklist. The next step in the checklist has you unload the main hydraulic pump which effectively makes that system inoperative and I did not want to shut a system down unnecessarily if the problem was indication only and not mechanical. A short time later; I observed the fluid quantity drop to 16% and then; after some additional time; finally to 15%. At that time; I asked my FO to unload the A system hydraulic pump and complete the checklist which ends with '...Land as soon as practical...'. My FO and I reviewed the Cessna 750 checklist page which defines this and agreed that with the hydraulic system secured; and no other abnormal indications; nor any catastrophic failure; we did not need to land immediately at the nearest airport. We were over the northern plains states at FL430; airspeed approximately .89M-.90M and fuel was not an issue as I had planned to tanker additional fuel back to base. We began reviewing various suitable airports within several hundred miles of our position and determined that many were either below minimums for the available instrument approach; or the prevailing winds were not well suited for an approach with a only the B hydraulic system and the Rudder Standby System. My FO and I discussed several options for landing; the first being the possibility of landing in ZZZ1 which was several hundred miles from our current position; but appeared the closest suitable major airport with light winds; relatively clear skies. At this point; I asked my FO to bring up the weather at our filed alternate [California]. At that time; the weather there was reported as VFR; winds that favored the active runway. I asked my FO to change our destination to ZZZ even though this was substantially further away. My reasoning was that ZZZ provided an excellent balance between getting our passengers to their destination; specialized repair capability for the aircraft; close proximity to our home base; as well as suitable multiple runways and emergency capabilities. I discussed my thought processes with my FO and reviewed other various options. My FO stated she agreed with continuing to ZZZ instead of diverting to ZZZ1.During the descent into ZZZ; we began to receive weather reports that showed substantial weather deterioration with many storm cells moving over the airport. My FO and I again discussed other landing options; but came to the conclusion that ZZZ was still our best one. It was at this point that my FO reminded me that we had not declared an emergency; nor informed ATC of the loss of the A hydraulic system. I immediately asked my FO to report our condition to Approach and communicate with the ZZZ tower that we would need time to complete the manual extension of the landing gear; various checklists; and would prefer a longer than normal final on the ILS. Additionally; we informed ATC that we would not be able to clear the runway on our own after landing. Approach and ZZZ Tower worked us as priority in the airspace for our arrival and I executed an uneventful approach and landing; using the predicted amount of runway for our condition.Looking back; the decision to carry on to ZZZ was NOT CORRECT. We should have landed in ZZZ1; or another suitable airport much closer to our position when the hydraulic issue presented itself. To continue on with a primary hydraulic system inoperative for an extended amount of time is less than ideal judgment and I believe several human factors contributed to this. Among them; a Target Fixation and Mission First mentality: I had been dealing with the other previous trip interruptions and cancelations due to maintenance issues before launching on this trip. There had been two chronic problems; unrelated to the hydraulic fault; that had just recently been resolved the night before and I did not want to down the aircraft at another out-station with the additional expense of putting our passengers on the airlines again. Also; Fatigue: As part of the continuing unrelated maintenance issues; I had recently traveled to the service center to pick up the current airplane; in addition to continuing to fly trips on our company's other aircraft and had been at a high activity level for an extended amount of time.




Synopsis: CE750 Captain experienced a CAS message 'HYD VOLUME LOW A' at FL430 a few minutes after level off. The applicable checklist directed that the system be unloaded by turning off the engine driven pump and ends with 'land as soon as practical.' The reporter elected to continue to an alternate that was two hours ahead and closer to destination.