Date: 201905
Local time of day: 1801-2400
Location: ZZZ.ARTCC, US
Light: Daylight
Aircraft: B737-700
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Fuel Booster Pump
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Flying
Reporter qualification: Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Anomaly: Aircraft Equipment Problem Critical; Inflight Event / Encounter Fuel Issue
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Flight Crew Diverted; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Landed As Precaution; General Flight Cancelled / Delayed
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: During climbout and then a level off at FL390; I began to select my charts for the arrival. While digging through [them]; the Captain mentioned 'Wow; we have a large imbalance. What is going on?' I put my iPad down and he began running through the QRH. We determined there was fuel in the center tank but the left tank was also feeding. Tank 2 was stuck closed or not operating. We tried a few different brainstorm ideas and talked while he ran through the QRH Fuel Leak pages. We determined the aircraft was being run off both the center tank and the left tank. Turning the center tank off with fuel; the aircraft was then running off tank 1 and creating a larger imbalance. Turning the center pumps back on now had the aircraft burning fuel from center and Tank 1. Tank 2 quantity never changed. We troubleshot the idea that we could either allow the imbalance to get worse or shut off the left pumps; but eventually the center tank would be empty and we questioned if engine one would flame out with no wing tanks on the left side on. We even opened the crossfeed; if I remember correctly; but even then the right side fuel was not accessible. Captain briefed the Flight Attendants. I; the FO; flew the aircraft; got a clearance to [a nearby alternate] and began to setup the radios; the FMS and the pressurization panel. I also texted Dispatch. I advised Captain; when he came back from the interphone; that I was ready for him to listen to a short brief. I briefed him of our clearance and the approach and he got the speeds and weather. I concluded the briefing and called for the Descent Checklist; and followed up with 'Hey; let's run through the Diversion Checklist really quick.' After the workload slowed down we were given a runway change and had to re-brief and reprogram the box. I navigated direct via LNAV. Shortly after I called the airport in sight; as the Captain got busy getting us a gate for the fire trucks to follow us to. We were cleared for the visual. I elected to use LNAV/VNAV; set 5;300 feet and we started down. Shortly inside the marker; we side-stepped to 1R; landed flaps 40; autobrakes 3. The touchdown was normal rate of descent and normal. Aircraft kept banking left; then right; due to the large imbalance. I clicked off the autopilot during the side-step; had Captain throw something in the box then used LNAV/VNAV for 1R. We landed; taxied off runway and fire trucks asked if they could escort us. We taxied to [gate] without further issues. Maintenance met us along with Maintenance Supervisor. There were a few Gate Agents; including one I assume was a Supervisor. We move a lot of metal; things happen. It would be cool if the Boeing aircraft had some sort of recall or scratch pad message when the fuel acts up. One thing I did want to add; was that I never want to inconvenience our passengers or others. However; it seemed like when we diverted there was this huge rush to swap aircraft and get us on our way. I wish other work groups would have let us talk with Maintenance in a slow calm manner; I just felt very rushed; as if we had to get going immediately again. Sometimes diversions or situations need a little bit of 'let's let our blood pressure reset a little' before we fly again.




Synopsis: B737-700 First Officer reported diverting to an alternate when a fuel imbalance developed related to faulty center tank and tank 1 fuel pumps.