Date: 201412
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: IMC
Weather elements / visibility: Rain
Light: Daylight
Aircraft: Citation X (C750)
Operator: Air Taxi
Operating under: Part 135
Flight plan: IFR
Mission: Passenger
Flight phase: Parked
ATC / advisory: Ramp ZZZ
Aircraft component: Fuel System
Component problem: Malfunctioning; Improperly Operated
Reporter organization: Air Taxi
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Confusion; Human-Machine Interface; Time Pressure; Training / Qualification
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Ground Event / Encounter Other / Unknown
Detector: Person Flight Crew; Person Ground Personnel
When detected: Aircraft In Service At Gate
Result: General Flight Cancelled / Delayed; General Maintenance Action
Contributing factors: Aircraft; Human Factors
Primary problem: Aircraft

Narrative: Arrived at the airport at XA pm for an  XC pm go with a 2 hour slide.  Rain was moderate to heavy and I decided to do the external preflight then; to take advantage of what little daylight remained.  Aircraft was a new assignment; having just been out of maintenance. External was completed and had my partner turn on the batts to read the fuel on board. It was 4;600 lbs. We left the plane and returned to the FBO. Not wanting to fire up the APU; to save gas; noise; and comply with new company APU usage memo. About an hour prior to departure; we left for the plane to start prepping for the flight; it was then that I was called by dispatch with concerns of the second segment climb and also a discussion of a required fuel stop. I quickly left the airplane without doing a cockpit prep; in order to double check the weather and to get the faxed release that; up till then; was not available due to we were not released until then. While in the FBO I ordered fuel to bring the load to 9;000 lbs.  My partner was at the plane at that time; trying to manage a very large PAX catering order and do his cabin checks. I returned to the airplane late; about XB:30 pm because the fax machine in the FBO was very busy. Upon arrival; my partner was still handling the catering issue; but the APU was up and we were fueled. I quickly entered the cockpit anxious to run numbers for the flaps 5 departure due to our load and weather. A cursory glance at the cockpit suggested all was well and so I went about correcting the fuel order because I noticed we were about 200 lbs shy of 9;000 lbs. Normally; I would have let this lie and would go about running my cockpit prep duties but because of the weather; headwinds and the possibility of being with the APU on for two more hours due to the slide; I called the FBO; and requested 50 gallons more.Sometime during this phone call; I get a shout from my partner and a ramp member saying; fuel is spilling out of the left wing overflow vent. At first; I could not see it; it was raining so hard everything looked like it was dripping; falling off the wing and empennage. But as I went closer; it was there; fuel was indeed pouring out and going onto the Tarmac mixing with at least 3/4 inch of rain water. I immediately told my partner to kill the APU and power off the plane while I attempted to shake the left wing tip in order to close the fuel valve. Now that sounds corny but about a year ago; I had the same issue. I shook the wing tip vigorously and the spill stopped. When the mechanic arrived; he said; you did the right thing; sometimes dirt; debris prevents the fuel tank valve from closing when the tank reaches 3;500 lbs. By shaking it; you dislodged the debris allowing the valve to close well; this time it didn't work; and I told the ramp personnel to get help because I could not stop it. The next 10 minutes felt like infinity; I was on hold trying to reach maintenance; my partner was trying to reach our flight support folks; I had the ramp manager come up and tell me that this same plane; the same wing did the exact same thing a week or so ago. This just reinforced my position that it was the overflow valve that was the cause and I wanted help; and I needed it now. On top of that; the fire trucks arrive; lights everywhere and I finally glance over my shoulder and there is a fuel truck pumping fuel into the plane again! I mean with emergency equipment and about 20 personnel all over. I know; I asked for 50 gallons more; but at this moment!!! So; I run out get the fuel guy stopped; the crews have a 50 gallon drum containing the spilling fuel; and guys are setting up barricades to contain the contaminants. All the while I am still on the phone; trying to get to maintenance. Finally; I got through and hurriedly describe the situation and they say; AOG it. I am like; yeah; of course. Now I try to get hold of the customer service agent and tell her the plane is done. When finally a line mechanic shows up; boltsto the cockpit and finds the gravity cross flow valve engaged. He turns it off; and after what seemed like 2 minutes; the fuel stops leaking.First; let me say this: I should have caught that the gravity cross feed was engaged; but in retrospect; with the bad light conditions; I did not. You have to lean over and scan around the yoke and steering column to see that particular switch. It's not out in the open like being on an overhead panel that you can just look at and see a pattern; but you can believe me; I am going to look at that switch a lot more now! Second; in my attempt to try to communicate to all the company departments I was distracted and could not focus on the how and why. I was frustrated with the lack of response from company and I could not step back and think. My thought process was this; the outflow valve is stuck open; it is gushing fuel; and I can't stop it...I did not think of the gravity cross feed because--to my system knowledge--yes; the gravity cross feed will fill the low side tank to full; but that is where it should stop...just like we yaw the airplane when it is venting fuel in flight.  We are trying to close that valve. We can fly with 3;500 lbs on one side and 3;000 lbs on the other; but it gets difficult if it keeps venting and your imbalance grows; anyway; I wanted the fuel system checked out; because to me; it should have stopped at 3;500 lbs. Looking back; what I really learned is to forget about trying to let everyone know hey; we got a possible situation that will disrupt our passenger convenience. I should have stepped back and thought about going back to see if all was right with the cockpit switches...I guess I got stressed; with all that is going on with the current atmosphere here at company.  I wanted to fix the problem; but instead of stepping back. I instead concentrated on trying to let everyone know about this; that was secondary to the task at hand.




Synopsis: A Citation flight crew suffered a fuel spill event during fueling due to failing to notice the gravity cross flow lever was 'engaged.'