Narrative:

We operated aircraft X when we had to [divert] for a left side fuel leak. We were delayed around 45 minutes as we had agreed to refuse the first assigned aircraft due to safety issues related to two MEL's for auto speed brakes and a thrust reverser inoperative while the weather for [the destination] was showing thunderstorms; low ceilings; rain and mist for the entire portion of our arrival.after receiving a new aircraft and following a normal departure; we we received a fuel disagree prog 2 FMC message as we were approaching [our midway point] at 35;000 feet. We pulled the QRH and followed the procedures which had us compare the totalizer fuel to the computed fuel. At this time we realized that there was a significant disagreement (~4;000 pounds) between the computed fuel vs the totalizer fuel. We had bumped the cost index and speed up due to our delayed departure in an attempt to make up some time for our passengers so we knew our fuel burn was going to be higher but we didn't expect such a significant difference. We began to monitor the fuel burn out of the center tanks and the ca (captain) contacted dispatch for updated fuel burns at mach .80-.81 to compare with the original computed flight planned fuel burn. I was monitoring the center fuel tank and noted that at around 1:40:00 into the flight we had approximately 4800 lbs in the center tank and it appeared to be burning at a higher than normal rate when we compared the burn per minute from our indicated fuel flow compared to the center tank totalizer. While I was monitoring the center tanks and overall aircraft state my captain was working with dispatch and comparing our various [performance] numbers from the various speed and cost indexes that we had. I don't recall the exact point in which we both suspected this to be an actual vs suspected fuel leak but the ca then requested a patch to dispatch to discuss the issue over voice while I took over pilot flying duties. At this point the ca was having a difficult time communicating with dispatch and [maintenance control] as his transmissions kept cutting out on him and he had to repeated himself repeatedly after every question he was asked. As we burned through the remaining center tank fuel and I told the ca I was going to turn both center tank pumps off and he confirmed that I should do so. After approximately 5 or so minutes after turning the center pumps off we saw a noticeable imbalance between the left and right fuel qualities. It began with a small 300 lb imbalance and eventually became 1000 lbs within less than 30 minutes which was the time noted in the QRH with regards to a suspected fuel leak. At this point while the ca was talking with dispatch; [maintenance control] and the [chief pilot] I called back to the purser and asked if she could go back after of the wings and look for any signs of a contrail or fluid that was coming from one wing but not the other. After several minutes she called me back over the intercom and we had a brief discussion of what she saw. She then went back to double check what she saw visually and confirmed that there was something streaming off the left side engine but not the right. I relayed this information to the ca who the told dispatch; the [chief pilot] and [maintenance control] of the new information. It was agreed then that this was an actual fuel leak and we should divert to the nearest suitable airport. Dispatched informed us that ZZZ was the best airport as it was only 80 miles away and we agreed. The ca had me communicate to ATC of our intentions to divert to ZZZ and a request for emergency equipment to meet us upon landing. While I flew the aircraft and talked to ATC the ca began to brief our flight attendant's (flight attendants) of our intentions to divert to ZZZ. Once we were advised that ZZZ was our best divert airport; I sent a request for an updated ATIS and started to configure the box for a divert and approach into ZZZ. I also sent for landing numbers from dispatch; communicated with ATC with regards to souls on board; fuel remaining and any assistance needed as the captain finished briefing the flight attendant's and finished what was remaining in the QRH. At this point we were less than 15 minutes from landing as we brief the approach; exit procedures and any other contingency's with regards to our emergency. During our brief I noted and told my ca that our landing weight per the FMC was showing ~196k lbs and that our totalizer was showing 23.4; our planned landing fuel was 23.0 so I had pulled flaps 30 landing numbers for him at ~196k if he was ok with that which he was. After finishing our descent checklist I called our purser and advised her that we were less than 10 minutes for landing and would be on the ground shortly. We flew a normal visual approach and landing into ZZZ follows by a left turnoff from runway xxl. After turning off runway xxl and while holding on taxiway 1 we had a discussion with ground about our intentions. It was determined that the emergency crews could actually smell fuel as we landing and believed we had a leak. As they approached us for a visual confirmation they confirmed that there was a 'pretty good leak' off the left engine. We then shut the left engine down followed by the fuel pumps in an attempt to stop the leak. We were also informed that we could not be towed to the gate with a fuel leak so we would need to be towed to the north ramp and deplane there. While this discussion was occurring we received a call from our purser advising us of a very strong smell of fuel that had filled up the cabin. We had begun to notice faint trances of a fuel smell ourselves in the flight deck and began a juggling act of trying to get a hold of company ops through the [chief pilot] to find a tug to tow us; attempting to stop the flow of fuel off of the left engine; communicating with ground crews of any injuries; monitoring the fuel vapors within the cabin of the aircraft and discussing the possibility of opening up two main cabin doors per the request of the flight attendant's to air out the cabin as smell was becoming worse. During our discussions about how to stem the fuel leak off the left engine we decided to start the APU and shut down the right engine as well. After doing so and turning off all fuel pumps (minus the fwd left pump due to the APU usage) we were told that the smell was possibly getting better but the flight attendant's weren't sure if it was because the smell was dissipating or if they were just getting used to it. At this point the ca had a discussion of the situation with our [chief pilot] and told me to advise the flight attendant's to open up 1R and 4R to air out the cabin. I don't recall how long we were on the ground for after landing but shortly after opening the cabin doors someone was able to find a tug and they were able to get it out to us to tow us to the north ramp where buses were waiting with a jet bridge to deplane the passengers. The fuel leak had mostly subsided at this point and we had the flight attendant's close both 1R and 4R so that we could be towed to the north ramp for deplaning. After deplaning the aircraft from 1R we had the flight attendant's disarm the rest of the doors and were going to deplane ourselves when we were asked by company ops if we could remain on board to monitor the aircraft as it was towed to a new position. While this as occurring I was in contact with the [chief pilot] and later the hotel desk in an attempt to secure hotel rooms as we had no further information about our schedule. After a long delay after the final tow; we ended up having to self-help with our hotel rooms due to various issues; including a lack of hotel rooms due to [local events]. Eventually arrived at our hotel [very late at night]. We then later realized that we did not and were not asked to run the human factors checklist at any point after arriving in ZZZ.

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Original NASA ASRS Text

Title: B757 First Officer reported a fuel leak from the left engine area; resulting in a diversion.

Narrative: We operated Aircraft X when we had to [divert] for a left side fuel leak. We were delayed around 45 minutes as we had agreed to refuse the first assigned aircraft due to safety issues related to two MEL's for auto speed brakes and a thrust reverser INOP while the weather for [the destination] was showing thunderstorms; low ceilings; rain and mist for the entire portion of our arrival.After receiving a new aircraft and following a normal departure; we we received a FUEL DISAGREE PROG 2 FMC message as we were approaching [our midway point] at 35;000 feet. We pulled the QRH and followed the procedures which had us compare the totalizer fuel to the computed fuel. At this time we realized that there was a significant disagreement (~4;000 LBS) between the computed fuel vs the totalizer fuel. We had bumped the cost index and speed up due to our delayed departure in an attempt to make up some time for our passengers so we knew our fuel burn was going to be higher but we didn't expect such a significant difference. We began to monitor the fuel burn out of the center tanks and the CA (Captain) contacted dispatch for updated fuel burns at Mach .80-.81 to compare with the original computed flight planned fuel burn. I was monitoring the center fuel tank and noted that at around 1:40:00 into the flight we had approximately 4800 lbs in the center tank and it appeared to be burning at a higher than normal rate when we compared the burn per minute from our indicated Fuel Flow compared to the center tank totalizer. While I was monitoring the center tanks and overall aircraft state my Captain was working with dispatch and comparing our various [performance] numbers from the various speed and cost indexes that we had. I don't recall the exact point in which we both suspected this to be an actual vs suspected fuel leak but the CA then requested a patch to dispatch to discuss the issue over voice while I took over pilot flying duties. At this point the CA was having a difficult time communicating with Dispatch and [Maintenance Control] as his transmissions kept cutting out on him and he had to repeated himself repeatedly after every question he was asked. As we burned through the remaining center tank fuel and I told the CA I was going to turn both center tank pumps off and he confirmed that I should do so. After approximately 5 or so minutes after turning the center pumps off we saw a noticeable imbalance between the left and right fuel qualities. It began with a small 300 lb imbalance and eventually became 1000 lbs within less than 30 minutes which was the time noted in the QRH with regards to a suspected fuel leak. At this point while the CA was talking with Dispatch; [Maintenance Control] and the [Chief Pilot] I called back to the purser and asked if she could go back after of the wings and look for any signs of a contrail or fluid that was coming from one wing but not the other. After several minutes she called me back over the intercom and we had a brief discussion of what she saw. She then went back to double check what she saw visually and confirmed that there was something streaming off the left side engine but not the right. I relayed this information to the CA who the told Dispatch; the [Chief Pilot] and [Maintenance Control] of the new information. It was agreed then that this was an actual fuel leak and we should divert to the nearest suitable airport. Dispatched informed us that ZZZ was the best airport as it was only 80 miles away and we agreed. The CA had me communicate to ATC of our intentions to divert to ZZZ and a request for emergency equipment to meet us upon landing. While I flew the aircraft and talked to ATC the CA began to brief our FA's (Flight Attendants) of our intentions to divert to ZZZ. Once we were advised that ZZZ was our best divert airport; I sent a request for an updated ATIS and started to configure the box for a divert and approach into ZZZ. I also sent for landing numbers from dispatch; communicated with ATC with regards to souls on board; fuel remaining and any assistance needed as the Captain finished briefing the FA's and finished what was remaining in the QRH. At this point we were less than 15 minutes from landing as we brief the approach; exit procedures and any other contingency's with regards to our emergency. During our brief I noted and told my CA that our landing weight per the FMC was showing ~196k lbs and that our totalizer was showing 23.4; our planned landing fuel was 23.0 so I had pulled flaps 30 landing numbers for him at ~196k if he was ok with that which he was. After finishing our descent checklist I called our purser and advised her that we were less than 10 minutes for landing and would be on the ground shortly. We flew a normal visual approach and landing into ZZZ follows by a left turnoff from runway XXL. After turning off runway XXL and while holding on taxiway 1 we had a discussion with ground about our intentions. It was determined that the emergency crews could actually smell fuel as we landing and believed we had a leak. As they approached us for a visual confirmation they confirmed that there was a 'pretty good leak' off the left engine. We then shut the left engine down followed by the fuel pumps in an attempt to stop the leak. We were also informed that we could not be towed to the gate with a fuel leak so we would need to be towed to the north ramp and deplane there. While this discussion was occurring we received a call from our purser advising us of a very strong smell of fuel that had filled up the cabin. We had begun to notice faint trances of a fuel smell ourselves in the flight deck and began a juggling act of trying to get a hold of company ops through the [Chief Pilot] to find a tug to tow us; attempting to stop the flow of fuel off of the left engine; communicating with ground crews of any injuries; monitoring the fuel vapors within the cabin of the aircraft and discussing the possibility of opening up two main cabin doors per the request of the FA's to air out the cabin as smell was becoming worse. During our discussions about how to stem the fuel leak off the left engine we decided to start the APU and shut down the right engine as well. After doing so and turning off all fuel pumps (minus the fwd left pump due to the APU usage) we were told that the smell was possibly getting better but the FA's weren't sure if it was because the smell was dissipating or if they were just getting used to it. At this point the CA had a discussion of the situation with our [Chief Pilot] and told me to advise the FA's to open up 1R and 4R to air out the cabin. I don't recall how long we were on the ground for after landing but shortly after opening the cabin doors someone was able to find a tug and they were able to get it out to us to tow us to the north ramp where buses were waiting with a jet bridge to deplane the passengers. The fuel leak had mostly subsided at this point and we had the FA's close both 1R and 4R so that we could be towed to the north ramp for deplaning. After deplaning the aircraft from 1R we had the FA's disarm the rest of the doors and were going to deplane ourselves when we were asked by company ops if we could remain on board to monitor the aircraft as it was towed to a new position. While this as occurring I was in contact with the [Chief Pilot] and later the hotel desk in an attempt to secure hotel rooms as we had no further information about our schedule. After a long delay after the final tow; we ended up having to self-help with our hotel rooms due to various issues; including a lack of hotel rooms due to [local events]. Eventually arrived at our hotel [very late at night]. We then later realized that we did not and were not asked to run the Human Factors checklist at any point after arriving in ZZZ.

Data retrieved from NASA's ASRS site 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.