B737 Fuel leak

[Flying_Tuur]

On the B737NG, a checklist is published for an inflight engine fuel leak.
How can one be sure that the leak is in the engine, and not the fuel tank?
I reckon that the best thing to do is to follow this checklist (also on the B737-EFIS, where this checklist is not published). If the fuel continues to dissappear, you will have a leak in the tank, and you could restart the engine you did shut down, and use the remaining fuel in the leaking tank, and eventuelly a crossfeed from the good tank.

Any other ideas on how to check where the leak is?

On the BAe146 we had a complete troubleshooting for fuel leaks. In the event of a leak in the fuel line towards the engine, we could let the engine run on its own fuel suction. This way the fuel lines were not under pression, so the fuel would not leak, instead because of the suction from the mechanical engine fuel pumps, you would suck the fuel from the engine, like a gravity feed, and additional where the leak is, some air would be sucked in as well. The engine would mosty probably not perform at high regimes, but an idle regime would be sufficient, and it would allow you to keep the engine GEN and/or the engine driven hydraulic pump.

Since this is an item boeing does not seem to cover, I expect 10 different companies to have 10 different procedures..

[320DRIVER]

On the A320 we use the FUEL USED indication. Since the FF transducer is located very close to the engine, if the F USED value is greater than on the other engine it would indicate a leak downstream of the transducer, hence in the engine. If the value is the same, it would indicate a leak before the transducer i.e. not in the engine.

I think you can access the F USED indication on the 737 by pressing something on the Engine Display if my memory serves me well. This was a B737-3/4/5 i.e. dunno about the NGs.

Another point re: fuel management is that a good check is that for every fuel check, add FOB + F USED and this should be equal to your departure fuel.

[john_tullamarine]

That may be all well and good ... (and Boeing, like all manufacturers with any sense, will give advice with a keen eye to their own potential liability) ... but I suggest that the value of the earlier recommendation lies in picking up gross flight by flight errors.

A similar philosophy/technique often is employed on freighters with on board CG systems ... there is invariably an error of some magnitude ... but, for the crew, this error is more or less predictable more or less most of the time ....

What the crew ought to be looking out for is those occasional times when the apparent error suddenly changes with a degree of significance. Sure this might mean not much at all - but it could just save your neck if you elect to get the ginger beers to check it out prior to departure.

I can recall a couple of occasions where a VERY relieved crew gave thanks to the training system which had indoctrinated them in this sort of checking regimen with both fuel and CG calculations.

I may be a bit of a dinosaur but I strongly adhere to the credo that the more the technical complexity and reliance on computerised systems, the more there is the odd likelihood of (especially) software glitches causing subtle problems which can bite pilots on the tender parts without much warning ... the wise pilot keeps as many options as possible open to protect him/herself .... and uses whatever reasonable techniques are available to give the crew an edge over the machinery's foibles ..