Narrative:

About 450 NM from ZZZ we were preparing for descent by obtaining the ATIS and running the numbers on the performance computer. All the numbers were normal; briefed up the visual approach; and continued to fly the arrival into ZZZ. At about FL240; the first officer/pilot flying (PF) made mention about the aircraft requiring more trim since ATC had slowed us to 250 knots on the arrival. I then noticed that the left fuel gauge was indicating approximately 1450 lbs of fuel and the right main tank indicating approximately 8700 lbs of fuel. I immediately looked up at the fuel panel to verify that the crossfeed valve was closed and made sure a fuel pump had not failed. It was closed; light out and all pumps on. I started to think that we had a fuel leak; but remembered that the fuel was in balance (within 350 lbs) not 30 minutes prior when we ran the performance computer numbers. My concern was the large imbalance. We notified the flight attendants that we had a fuel imbalance and would be lowering the gear. We then notified ATC that we needed to hold until the balance was close enough to continue. We went into holding. I contacted dispatch over ACARS to report up on dispatch/maintenance frequency so as to speak directly with them. Maintenance made sure we checked the circuit breaker for the crossfeed valve was in; it was. I noticed that during the descent with both engines providing power; we were only burning about 4400 lbs per hour. I was concerned that we needed to burn the fuel much faster to lessen the impact of the imbalance. I instructed the first officer to slowly reduce the number one engine to idle and advance the number two engine to max cruise thrust. This action was taken and the fuel flow increased to slightly more than 7000 lbs/hr burn. Dispatch reran the numbers and concluded that ZZZ1 would be the alternate. To remain legal; we needed to arrive at ZZZ with 5.1 and then continue to ZZZ1 if need be. We left holding with 6500 lbs total and continued to use the right engine for the thrust. After our discussion with dispatch and maintenance; the first officer and I were both comfortable landing with an imbalance of 3000 to 3500 lbs. We were about 10 NM from ZZZ when we returned the aircraft to normal operation with both engines providing thrust. We landed without incident and taxied to the gate. No passengers made comments about the asymmetrical thrust we were using. First officer did a great job of the flying the aircraft enroute. I assumed control after we left the holding pattern. Maintenance met the aircraft at the gate. A maintenance person had heard our conversation with dispatch/maintenance control over the radio. He knew what was going on. The mechanics inspected the aircraft and said that they were going to replace the crossfeed valve. When we landed; the left main fuel tank was indicating 1450 lbs and the right main was indicating approximately 4500 lbs. We entered a writeup in the logbook and let maintenance continue their work. We left the maintenance guys with the aircraft. Closer vigilance of the fuel gauges could have possibly mitigated the imbalance. We would have been manipulating the fuel pumps to correct the problem. I have not talked to maintenance as to whether this would have worked.

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Original NASA ASRS Text

Title: B737 Flight Crew experiences a large fuel imbalance during preparation for descent and landing. Asymmetrical thrust was used to decrease the imbalance; landing about 3000 pounds out of balance.

Narrative: About 450 NM from ZZZ we were preparing for descent by obtaining the ATIS and running the numbers on the Performance Computer. All the numbers were normal; briefed up the visual approach; and continued to fly the Arrival into ZZZ. At about FL240; the First Officer/Pilot Flying (PF) made mention about the aircraft requiring more trim since ATC had slowed us to 250 knots on the arrival. I then noticed that the left fuel gauge was indicating approximately 1450 lbs of fuel and the right main tank indicating approximately 8700 lbs of fuel. I immediately looked up at the fuel panel to verify that the crossfeed valve was closed and made sure a fuel pump had not failed. It was closed; light out and all pumps on. I started to think that we had a fuel leak; but remembered that the fuel was in balance (within 350 lbs) not 30 minutes prior when we ran the Performance Computer numbers. My concern was the large imbalance. We notified the Flight Attendants that we had a fuel imbalance and would be lowering the gear. We then notified ATC that we needed to hold until the balance was close enough to continue. We went into holding. I contacted Dispatch over ACARS to report up on Dispatch/Maintenance frequency so as to speak directly with them. Maintenance made sure we checked the circuit breaker for the crossfeed valve was in; it was. I noticed that during the descent with both engines providing power; we were only burning about 4400 lbs per hour. I was concerned that we needed to burn the fuel much faster to lessen the impact of the imbalance. I instructed the First Officer to slowly reduce the number one engine to idle and advance the number two engine to Max Cruise Thrust. This action was taken and the fuel flow increased to slightly more than 7000 lbs/hr burn. Dispatch reran the numbers and concluded that ZZZ1 would be the alternate. To remain legal; we needed to arrive at ZZZ with 5.1 and then continue to ZZZ1 if need be. We left holding with 6500 lbs total and continued to use the right engine for the thrust. After our discussion with Dispatch and Maintenance; the F/O and I were both comfortable landing with an imbalance of 3000 to 3500 lbs. We were about 10 NM from ZZZ when we returned the aircraft to normal operation with both engines providing thrust. We landed without incident and taxied to the gate. No Passengers made comments about the asymmetrical thrust we were using. First Officer did a great job of the flying the aircraft enroute. I assumed control after we left the holding pattern. Maintenance met the aircraft at the gate. A Maintenance person had heard our conversation with Dispatch/Maintenance Control over the radio. He knew what was going on. The Mechanics inspected the aircraft and said that they were going to replace the crossfeed valve. When we landed; the left main fuel tank was indicating 1450 lbs and the right main was indicating approximately 4500 lbs. We entered a writeup in the logbook and let Maintenance continue their work. We left the Maintenance guys with the aircraft. Closer vigilance of the fuel gauges could have possibly mitigated the imbalance. We would have been manipulating the fuel pumps to correct the problem. I have not talked to Maintenance as to whether this would have worked.

Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.