B737-700
Time Pressure; Confusion; Communication Breakdown; Troubleshooting; Workload
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Fuel Issue
Flight Crew Overcame Equipment Problem; Flight Crew Took Evasive Action
Chart Or Publication; Aircraft; Company Policy; Procedure; Manuals
At 38;000 FT; the First Officer noticed that fuel was only being used from one tank. It was only a 200-LBS imbalance; but it was clearly getting worse. We checked the crossfeed and the light didn't work using the lights test and then looked up where the circuit breaker was. The circuit breaker was tripped (it's right by the shoulder harness). Right as we noticed this; the fuel imbalance indicator turned Amber; we had gone from 200 LBS to 1;000 LBS in the time it took to look up and check the breaker. We used ACARS to ask Dispatch for advice from Maintenance Control; who replied; 'follow QRH' with no additional comment. This is where this report is important: the QRH procedure does not work; it is incorrect. The QRH has two lines of logic; one with the breaker tripped; one without. The old QRH was simpler: 'fuel balance maintain.' The QRH has been changed; probably to deal with the crews that mistakenly performed engine shutdowns for using the fuel leak procedure for this same circuit breaker problem. The difficulty is the new procedure doesn't work in the air. It tells you to check the breaker (good); but then it gives this instruction: Verify that sufficient fuel is available to both engines to complete the flight. There is no way of either a) knowing if the imbalance was going to drain a tank or b) if it didn't; know that control could be maintained with a severely out-of-balance aircraft. Remember; we were at 1;000 LBS of imbalance within just a couple minutes of noticing: we had 50 minutes to go; to land at absolute destination airport minimums. The nearest airport with good weather was more than an hour away. I suspect this QRH procedure was created in the simulator. In the airplane; once it starts getting out of balance; it gets worse very quickly. The wrench in the works is Note 2; 'It is not possible to determine the position of the fuel crossfeed valve.' They took out 'maintain fuel balance'; the old procedure; presumably because there is no way to know if the valve is open enough to be able to safely shut off pumps to one tank at altitude. We did not want to do this; we were at 38;000 FT. However; following the circuit breaker tripped logic; the QRH had a hard [stop]. This is one of the times I felt like I was out of options. The destination was at minimums; (300-1; the lowest for Runway 4); there was nothing below us that was good; our alternate was more than an hour away and I was now over 1;500 LBS of imbalance and getting worse by the minute. Adjusting rudder trim to lift the heavy wing didn't make a difference. There was zero chance that I could make it to destination with more than minimum fuel in the low tank; it was possible it could even run dry (remember; we're already in the Amber 'IMBAL'). If the imbalance got to 4;000 LBS; or 3;000 or whatever; I assumed the autopilot would kick off and the airplane would be difficult to control. It was possible I was going to miss the approach into our destination regardless; since weather was at minimums with freezing drizzle. Shooting an approach to 300 FT with a huge weight imbalance; then diverting; no way. So now what? We agonized over the breaker. Is 'fuel crossfeed' the same as a 'fuel control' circuit breaker? I've been flying Boeings for 20 years and I don't know the answer. We both agreed it wasn't; but either way; I am loathe to touch any breaker that says 'fuel.' Do I crossfeed; and run the chance that the crossfeed is only partially open and I flame out an engine? The QRH certainly does not call for crossfeeding. Do I divert? I can't; my alternate is an hour away and I have no intention of letting the imbalance get more than 500 more pounds; since I don't know how the airplane will handle; it was already flying sideways at 1;500. Even if there was a closer 'nearest suitable'; from 38;000 FT the imbalance would put one tank into 'min gas' and give me a possible controllability problem. This was one of those times when QRH procedures didn't match real life. I had no tools to 'verify if sufficient fuel is available to both engines to complete the flight;' I don't know how to do that. How fast is the imbalance going to progress? I assume it gets faster as the wing gets heavier. I don't know how many minutes I have for it to get to emergency fuel. I don't know where my destination is; is it ZZZ or ZZZ1? Nearest suitable off-line that was above minimums? What if I missed the approach? The QRH doesn't say what to do next. It gives an impossible instruction ('determine something you can't determine with the tools you have') then doesn't tell you what to do next. Divert to nearest suitable? Doesn't say that. Mine was upstate [far distance from destination]; so not an option. Fuel balance: manage? Doesn't say that. Reset the breaker? Doesn't say that either. In the end; we read (out loud) the QRH instructions about resetting circuit breakers. 'An in-flight reset should only be accomplished if; in the judgment of the Captain; regaining use of that system is critical to the safe conduct of flight.' I determined that the safest course of action was to attempt a reset; then the second safest was to attempt to manage imbalance by shutting off fuel pumps; and the third safest to continue on with no action. I reset the breaker (the crossfeed operated normally) I contacted Maintenance Control on the ground and made the Info Only write-up after explaining my decision process; and proceeded on. The QRH procedure needs to be updated to list the options in order of desirability: a) reset breaker; b) risk flameout by turn off fuel pumps to manage fuel or c) immediately land at nearest suitable (which wouldn't have worked in my case due to low weather). There isn't time to do anything else other than these three. Including guidance on how to determine 'sufficient' fuel would help as well.
A B737-700 crew discovers a fuel imbalance while in cruise at FL380. With the Fuel Crossfeed Circuit breaker tripped and because the QRH does not address all reset possibilities; destination weather was at minimums and arrival fuel would be at minimum safe quantity; the Captain reset the Cross Feed circuit which corrected the problem.