B737-800 flight crew reported recurring fuel imbalance during cruise. After landing flight crew observed puddles of fuel on ground and flight attendants reported strong fuel fumes in cabin.
Synopsis
B737-800 flight crew reported recurring fuel imbalance during cruise. After landing flight crew observed puddles of fuel on ground and flight attendants reported strong fuel fumes in cabin.
Narrative
Shortly after center fuel tanks were emptied; we began deviating around thunderstorms encountered to ZZZZ. I had shut off our center pumps with fuel even in both main tanks. Shortly thereafter; noticed a 500 lb imbalance between L and R tanks; with the R tank being low-strange; because fuel flow was slightly higher on L side. I opted to crossfeed; and we ended up with even tanks. Shortly thereafter; the right side again began to appear lower than L side. I crossfed again; and got the tanks to even. I then notified dispatch that I would be putting in a discrepancy and to please relay to Maintenance Control. Our fuel; when the problem first surfaced; was estimated to be 11.7 on landing; which was normal at the time. Though suspecting we had a fuel leak; I was hesitant to shut down the #2 engine; we were closing in on ZZZZ; and our left engine had a high (though within normal range; oil temperature). I asked our flight attendants to discreetly see if anything appeared normal outside our right wing; and they mentioned all appeared normal. We opted to stay high until going idle for descent into ZZZZ. By the time we touched down; we eventually had 6700 lbs. a shortage of 5000 lbs.After landing; we cleared the runway; and the aircraft had begun to have a strong fuel odor. I asked my FO to shut down engine #2; but the smell persisted. Our Flight Attendant's called and started to mention the cabin was smelling like fuel; and a few rampers with another airline kept motioning to our number 2 engine. I told apron we needed a gate ASAP; as I was hoping to prevent a panic which might cause further passenger issues. We got to the gate and quickly deplaned all passengers.I am curious if the incident is related to a maintenance write up on Day 0 for the #2 Engine Main Oil/Fuel Heat Exchanger leaking fuel during idle run and after shutdown.
Second reporter narrative
Under an hour prior to scheduled arrival in ZZZZ; flight crew observed a lateral imbalance between main fuel tanks. This occurred shortly after center fuel tank exhaustion over ZZZZ. Pilot flying (check pilot flying for currency/proficiency) implemented fuel balancing. I (first Officer/pilot monitoring) agreed. Also; at this time flight crew requested weather deviation west of course through ZZZZ1 airspace for hazardous buildups. Flight crew completed fuel balancing; and noticed decrease in expected arrival fuel. Flight crew initially assessed decrease in arrival fuel as result of lateral weather deviation. Flight crew then noticed another fuel imbalance (once again; tank 2 quantity approx 500 lb lighter than tank 1). Simultaneously flight crew noticed engine 1 oil temp significantly higher than engine 2 (118C vs ~70C) and lower oil pressure (48psi vs ~6psi) although still in normal range. Flight crew re-balanced fuel a second time; and then noticed additional decrease in arrival fuel (approx 8klbs; initially 11.5klbs). As flight crew resumed normal route after weather deviation; we began to suspect a non-normal condition in the fuel system specifically regarding engine #2. Flight crew assessed that ZZZZ by this point was the nearest suitable airfield. Once again; fuel imbalance detected a third time with tank 2500lb lower. Flight crew discussed the likelihood of a fuel leak and had flight attendants discreetly visually check aircraft right side for evidence. No evidence detected. Flight crew rebalanced fuel for a third and final time while commencing descent into ZZZZ. Flight crew discussed the potential risks of running fuel leak QRH procedure and ultimately shutting down engine 2; with oil temp & pressure close to limits on engine 1 over the water and elected to recover the aircraft without executing any non- normal procedures. A normal landing was made safely by the left seat pilot flying. After vacating runway and approaching gate; flight crew detected an odor of jet fuel which was confirmed by flight attendants. Captain directed a shutdown of engine 2; I agreed; and shut it down normally. Shortly thereafter; ground personnel began to approach the aircraft gesticulating to shut down engine 2 which had already been accomplished. The gate then became available; flight crew taxied in on engine 1; and requested Ops to expedite jet bridge to minimize delays in deplaning passengers. Flight crew shut down normally at the gate with 6.5klbs fuel remaining. Fuel odor began to subside. After shutdown; flight crew observed large puddle of fluids on ramp which had prompted response from ground personnel. A smaller puddle sat below engine 2 at parking location. Passengers and crew deplaned safely through jet bridge.Cause: Suspected malfunction & fuel leak from engine 2 fuel pump(s). Masked for majority of flight by use of center tank fuel overriding the manifold; and delayed assessment due to weather deviation affecting arrival fuel state. Over water route of flight and engine 1 oil data affected decision whether or not to pursue use of QRH for possible fuel leak which would ultimately have led to shutdown of engine 2.I'm not sure what could be done to preclude this ever happening again - maintenance personnel and flight crews do their best to maintain safety of flight at all times; and redundant systems/sound decision making practices enhance safety. It seems the fuel pump just decided it was time to stop working properly.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.