Narrative:

While in cruise at FL370 we got a fuel imbal indication on the left side. The first officer was flying and I took control of the aircraft to let her run the appropriate checklist and called the company to ask for guidance. After running the checklist we believed we had a leak and the next step is to shut down the effected engine. We decaled an emergency, shut down the left engine and proceeded to land at ZZZ. After landing I called our maintenance control and, while talking to them, learned that I might have mismanaged the xfeed system on the aircraft. Our airline has had some fuel leak problems with the B737 of which both the first officer and I were aware. I believe that this knowledge let us develop tunnel vision to the perceived in-flight anomaly. While discussion of these events in training and on the line is very useful, perhaps more emphasis should be put on looking past the apparent and delving into the problem. It is very difficult, in a 2-PERSON crew, to fly, communicate with ATC, company, flight attendants, and passenger while facing a time critical emergency. Supplemental information from acn 627014: during cruise flight, approximately 30 mins into the flight, the fuel imbal annunciator illuminated. After completing the checklist, a determination was made that there was a possible left tank fuel leak. The left tank quantity indicator continued to decrease. At about 5 mins after the discovery of fuel imbal, the imbal had increased to 2000 pounds. Considering this situation, the thoughts of losing more fuel and becoming increasingly out of balance, as well as possible fire, were in my mind. We decided to take the safest course of action by shutting down and securing the left engine and we diverted to the nearest suitable airport which was ZZZ airport approximately 50 mi away. Initially, I was the PF. The captain decided to xfer controls before we secured the engine so he was the PF and I was the PNF for the remainder of the flight. ATC gave us radar vectors to ZZZ and we landed without further incident. After we landed on the ground, taxied clear of the runway, and shut down the right engine, the fire and rescue team visually inspected the aircraft and found no evidence of leaking fuel. Given this outcome, I don't know if the problem was caused by internal fuel system malfunctions, a faulty fuel indicator, pilot error, or pilot judgement error.

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Original NASA ASRS Text

Title: B737-800 CREW SHUT DOWN #1 ENG AFTER THE FUEL IMBAL, ANNUNCIATOR ILLUMINATED.

Narrative: WHILE IN CRUISE AT FL370 WE GOT A FUEL IMBAL INDICATION ON THE L SIDE. THE FO WAS FLYING AND I TOOK CTL OF THE ACFT TO LET HER RUN THE APPROPRIATE CHKLIST AND CALLED THE COMPANY TO ASK FOR GUIDANCE. AFTER RUNNING THE CHKLIST WE BELIEVED WE HAD A LEAK AND THE NEXT STEP IS TO SHUT DOWN THE EFFECTED ENG. WE DECALED AN EMER, SHUT DOWN THE L ENG AND PROCEEDED TO LAND AT ZZZ. AFTER LNDG I CALLED OUR MAINT CTL AND, WHILE TALKING TO THEM, LEARNED THAT I MIGHT HAVE MISMANAGED THE XFEED SYS ON THE ACFT. OUR AIRLINE HAS HAD SOME FUEL LEAK PROBS WITH THE B737 OF WHICH BOTH THE FO AND I WERE AWARE. I BELIEVE THAT THIS KNOWLEDGE LET US DEVELOP TUNNEL VISION TO THE PERCEIVED INFLT ANOMALY. WHILE DISCUSSION OF THESE EVENTS IN TRAINING AND ON THE LINE IS VERY USEFUL, PERHAPS MORE EMPHASIS SHOULD BE PUT ON LOOKING PAST THE APPARENT AND DELVING INTO THE PROB. IT IS VERY DIFFICULT, IN A 2-PERSON CREW, TO FLY, COMMUNICATE WITH ATC, COMPANY, FLT ATTENDANTS, AND PAX WHILE FACING A TIME CRITICAL EMER. SUPPLEMENTAL INFO FROM ACN 627014: DURING CRUISE FLT, APPROX 30 MINS INTO THE FLT, THE FUEL IMBAL ANNUNCIATOR ILLUMINATED. AFTER COMPLETING THE CHKLIST, A DETERMINATION WAS MADE THAT THERE WAS A POSSIBLE L TANK FUEL LEAK. THE L TANK QUANTITY INDICATOR CONTINUED TO DECREASE. AT ABOUT 5 MINS AFTER THE DISCOVERY OF FUEL IMBAL, THE IMBAL HAD INCREASED TO 2000 LBS. CONSIDERING THIS SIT, THE THOUGHTS OF LOSING MORE FUEL AND BECOMING INCREASINGLY OUT OF BAL, AS WELL AS POSSIBLE FIRE, WERE IN MY MIND. WE DECIDED TO TAKE THE SAFEST COURSE OF ACTION BY SHUTTING DOWN AND SECURING THE L ENG AND WE DIVERTED TO THE NEAREST SUITABLE ARPT WHICH WAS ZZZ ARPT APPROX 50 MI AWAY. INITIALLY, I WAS THE PF. THE CAPT DECIDED TO XFER CTLS BEFORE WE SECURED THE ENG SO HE WAS THE PF AND I WAS THE PNF FOR THE REMAINDER OF THE FLT. ATC GAVE US RADAR VECTORS TO ZZZ AND WE LANDED WITHOUT FURTHER INCIDENT. AFTER WE LANDED ON THE GND, TAXIED CLR OF THE RWY, AND SHUT DOWN THE R ENG, THE FIRE AND RESCUE TEAM VISUALLY INSPECTED THE ACFT AND FOUND NO EVIDENCE OF LEAKING FUEL. GIVEN THIS OUTCOME, I DON'T KNOW IF THE PROB WAS CAUSED BY INTERNAL FUEL SYS MALFUNCTIONS, A FAULTY FUEL INDICATOR, PLT ERROR, OR PLT JUDGEMENT ERROR.

Data retrieved from NASA's ASRS site as of July 2007 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.