Date: 201811
Local time of day: 0001-0600
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Dusk
Aircraft: Citation X (C750)
Operator: Air Taxi
Flight plan: IFR
Flight phase: Climb
Airspace: Class B ZZZ
ATC / advisory: TRACON ZZZ
Aircraft component: Hydraulic System
Component problem: Malfunctioning
Reporter organization: Air Taxi
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Multiengine; Flight Crew Instrument
Anomaly: Aircraft Equipment Problem Critical
Detector: Automation Aircraft Other Automation
When detected: In-flight
Result: Flight Crew Returned To Departure Airport; Flight Crew Diverted; Flight Crew Landed in Emergency Condition
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: On this leg; I was initially the Pilot Monitoring; but elected to take the flight controls after the situation developed and became the Pilot Flying for the landing into ZZZ. `***[ATC was advised]; no injuries to crew or anyone on the ground; and no visible damage to the aircraft with the exception of a hydraulic fluid leak resulting from the mechanical failure in flight. No damage to anything on the ground. No passengers on board; crew only.We were called out on for a last minute trip from ZZZ-ZZZZ to reposition for a trip the next day. Aircraft X had just come out of MX for some minor write-ups; two light bulbs burned out and an adjustment to the cabin door. No previous hydraulic issues had been identified or written up in the 11 days I've been with this airplane; or from the previous crew. Airplane was preflighted normally inside and outside by both crewmembers as is my routine after MX. No discrepancies were noted. First officer was the Pilot Flying. Normal takeoff from ZZZ in good weather on Runway XXL. Landing gear retracted normally at positive rate; and flaps/slats were retracted normally at 400 feet AGL. We then turned right to heading 120 per Tower instructions and were passing through 500 feet MSL climbing to 5;000 feet MSL per clearance. We were handed off to ZZZ Departure who issued a clearance to climb to 15;000 feet MSL. At this point; we were climbing through about 1;000 feet MSL and received an amber Master Caution and an amber CAS message 'HYD VOLUME LOW A.' I immediately selected the ENG/HYD EICAS page which gives more information about the hydraulic systems; and noticed a rapid decrease in hydraulic system A fluid quantity.Hydraulic system A is critical on the Citation X; and is the only source of hydraulics for normal landing gear extension/retraction; nosewheel steering; and brakes. Fortunately; there are pneumatic emergency backup systems for landing gear blow down; limited nosewheel steering through accumulator pressure and limited pneumatic brake application. Hydraulic system B was functioning normally and powering the flight controls. However; there is a hydraulic B PTU (power transfer unit) whose function is to provide hydraulic pressure from the B side to the A side in the event the A side pumps fail. In our case; with a fluid loss on the A side; the B PTU will spin uncontrollably; overheat and possibly cause the hydraulic B system to also fail. This is managed by immediately pulling the HYD B PTU CONT circuit breaker on the Captain's side. This action was accomplished quickly per training and no further issues developed from the PTU or the B system. Hydraulic B side system functioned normally for the duration of the flight.Noticing the rapid fluid loss on the A side and noticing there was some residual but decreasing pressure in the system; I took control on the aircraft; quickly slowed the airplane below the landing gear extension speed of 210kts; and put the landing gear handle down. This was an attempt to use the residual pressure in the hydraulic A system to lower the landing gear. The nosewheel came down and locked within about 10 seconds. The red UNLOCKED light remain illuminated with the main wheels unlocked for about 1 minute. At this point; I directed Pilot Monitoring to notify ATC that we were returning to ZZZ and [requesting priority]. Pilot Monitoring did that; and began running the checklist for 'Landing with no hydraulic A system pressure.' After approx. 1 minute both main wheels locked down and the red UNLOCK light extinguished. 3 green / no red indicating the landing gear was safely down and locked.I requested Runway XX at ZZZ for landing which is [over] 13;000 feet long. This is the longest runway available and was selected because I knew we would not have normal braking. We ran the checklist and set up for a visual approach backed up with the ILS XX. The weather was fortunately excellent with winds 090/10; good visibility and clear skies.Per the checklist; we knew we had to keep feet off the normal brakes and use rudders only for steering. The emergency brake handle is located on the Captain's side and would be the only means to stop the airplane on the runway. Also available to help were some off the speedbrake panels and the right T/R. We briefed the landing several times knowing that it would be abnormal; feet off the brakes; emergency brake handle pull and hold. When using the emergency braking system; there is no anti-skid; so I could not brake too aggressively; thus the long runway and steady braking plan.We landed close to the numbers to maximize available stopping distance; on speed; but faster than normal due to limited to partial. Vref was 130kts in this configuration. As briefed; we did not attempt to use normal braking; got the nosewheel down on the runway; and used rudder to steer on the centerline. The emergency brakes were applied with a pull and hold of the handle and steady pressure. Pilot Monitoring held downward pressure on the elevator as briefed; and I transitioned to the tiller while holding the emergency brake handle. With the remaining accumulator pressure on the nosewheel steering now with the tiller I was able to keep the airplane on the centerline. Slowing through approx. 20 kts; I asked Pilot Monitoring to shut down both engines to remove any thrust that would cause us to roll forward. Pilot Monitoring did this; and at this point we had both engines shut down and APU running to provide electrical power. We came to a full stop approximately 9;000 feet down the runway. We had requested multiple times with the Tower that as soon as we were stopped we needed the airplane to be chocked. At this point; the airplane is completely disabled on the runway; unable to taxi; steer or stop; and unknown how many brake applications remained in the pneumatic emergency brake bottle. I was holding the emergency brake handle out to prevent the airplane from rolling. Emergency crew response was very slow. We asked again for chocks and waited several minutes. Pilot Monitoring then got out of the airplane and walked over to the fire crews and repeated the request. After about 5 minutes; Pilot Monitoring was able to get some chocks and chocked the nosewheel. At this point; I could release the emergency brake handle as the airplane would no longer roll.We elected to shut down the airplane completely and disconnect the batteries. At this point; we could not see any visible damage or fluid leaks. Fire department measured the brake temperature and nothing was too hot. We waited on the runway for approx. 10 minutes for the tug. Tug arrived and towed us back to FBO.After getting back to FBO; we checked the airplane again. Pilot Monitoring noted hydraulic fluid on the tail under the bottom of the left horizontal stabilizer and streaming back on the stinger. We also checked the hydraulic A fluid reservoir and confirmed the fluid level was zero.Event was immediately reported to Flight Control; spoke with [personnel] over the phone while still disabled on the runway. Also spoke with Chief Pilot and Maintenance Control while under tow.This was a mechanical failure of something in the hydraulic A system causing total fluid loss. I will leave this determination to MX dept to decide what course of action is necessary to prevent this from happening again.On the airport emergency equipment; response was unexpectedly slow. We asked repeatedly for chocks; and notified ATC and fire personnel well ahead of time that chocks would be necessary to keep the airplane from rolling with no brakes. I had to hold the emergency brake handle for 5 minutes until the chocks were finally put in place.




Synopsis: CE750 Captain reported a failure of hydraulic system A; resulting in a return to departure airport.