Fuel crossfeed and leak

[PENKO]

Why are flight departments so paranoid about crossfeeding fuel in case of a confirmed leak from a tank? I understand very well that it is a bad idea to feed fuel from the good tank to the leaking side, that's a definite no go, but what about the other way around?

Say you are flying over the ocean a long way from any airfield, are you just going to watch a wing tank loose all its fuel or are you going to try to use as much of what is left by crossfeeding the remaining fuel from the leaking side to your engines? According to my 320 QRH this is not an option.

Any idea why? Again, it is obvious why you would not want to just open the crossfeed valve, but I don't understand why we are not allowed to actively crossfeed (switching off the pumps on the 'good' tank).

[rudderrudderrat]

Hi Penko,

The QRH is written around the most likely scenario conceivable, then updated after an incident.
A fuel tank will usually develop a leak if it's damaged by debris from:
1) exploding engine (Qantas A380, Airtours 737 JL @ MAN)
2) tyre debris etc. (Concorde,)

I can't imagine why a fuel tank would suddenly develop a fuel leak mid ocean. However, if it did - I like your logic.

[bcgallacher]

Fuel tanks rarely leak but fuel line connections - 747 for example are prone to this - cause the same problem depending on location.

[BOAC]

Penko - I suggest you keep it quietly 'up your sleeve' as a sensible option. It was certainly an option we considered in military days - rather than seeing fuel dripping into the ocean. You need to be certain/sure where the leak is, of course as you could make things much worse.

I recall suggesting it to a 737 trainer who went into a shuddering fit and mumbled about QRH etc. I suspect he had never really been very short of fuel and watched some of the 'usable' go to waste.

[Avenger]

It is difficult to determine where the fuel leak is, but for arguement's sake let's assume we have a leak from the tank at rate xx, if we cross feed we may well end up with the max fuel imbalance being out of limits and possibly a low pump pressure problem etc etc. Whilst it makes sense to use the available fuel, operating outside the the QRH may be more hazardous.

[3holelover]

Again, it is obvious why you would not want to just open the crossfeed valve, but I don't understand why we are not allowed to actively crossfeed (switching off the pumps on the 'good' tank).

If I zero in on the word, "just", above, can I assume you know that to crossfeed at all you will indeed have to open the crossfeed valve? ... Now, here's the problem... Crossfeeding happens by pressure differential. You're assuming the tank with the leak, with pumps on, will still be providing more pressure in the plumbing than the side with no leak, with it's pumps off. But you have no way to be sure. In fact, if the leak is in some of the plumbing between the xfeed vlv and the pumps, you may well end up siphoning fuel from the non-leaking side, and you won't know it until you watch the quantity dwindle.

[PENKO]

Thanks for the replies so far, they are all very helpful.

3holelover, interesting point. I guess the simple answer is to monitor your good tank whilst crossfeeding. Sure there is a chance that you might start syphoning from the good tank, but proper monitoring should cover that. If however you do nothing you are guaranteed to loose a lot of good useable fuel. Which is the greater evil?

Avenger, the wing will empty anyway due to the leak. If wejust look at the 320 that is of no great consequence. Neither are dry running pumps, for which you get a warning.

So I guess it is safe to say that it all depends on the situation. A leak over Europe means you land asap without complicating the problem. A leak over the Atlantic, well...you better be sure what you are doing?

[TyroPicard]

but I don't understand why we are not allowed to actively crossfeed (switching off the pumps on the 'good' tank).

1.....Remember Air Transat.....
The simple answer is because the QRH tells you not to apply the FUEL IMBALANCE procedure.
It can take well over 30 minutes to confirm a wing leak - over Europe you should be on the ground by then.

Other factors... the QRH procedure only says "a leak from the wing may be suspected" (my bolding) - you do not know exactly where the leak is as 3holelover pointed out. If you choose to go against the QRH - which you are entitled to do if your course of action is safer....... not cheaper, safer .. just make sure you are right!

[BOAC]

Interestingly there is nothing directly in the 737 QRH for tank leak 'Engine leak' only.

Originally Posted by TP

Don't forget you have put the CTR TK PUMPs

- why is that done?

For penko - I know what I would do in the middle of nowhere with a wing tank leak leaving me with insufficient fuel to go anywhere. Just got to get it right!

[TyroPicard]

Morning BOAC..
CTR TK PUMPS go OFF during procedure, you then monitor wing tank quantities.. faster depletion on one side by >300kg in 30 minutes indicates a leak.. shut down the engine on the leaking side, if the leak stops it's the engine, if not it may be the wing tank.
CTR TK PUMPS go back ON after shutting down the engine to restore normal fuel feed - they feed the engine not the tank - so I will now edit my previous post!

[Meikleour]

PENKO: as Tyropicard says please revisit the Air Transat A330 fuel leak incident. The problem lies with establishing whether the leak is from the actual TANK wall or some of the piping from it!

Incidently, the fuel leak procedure for the A330 is a bit more "punchy" than that for the A320 and may have gone some way to explaining the Air Transat`s crew behaviour.

Many years ago the B707 did in fact have a fuel leak procedure which encouraged the use of the leaking tank prior to all the fuel from it being lost however the more modern philosophy today does not allow this for very good reasons.

[PENKO]

Meikle, as you already state, the 330 is much more complex thant he 320. Usually you have just two tanks to deal with on the 320. So far the only reason offered against using the leaking fuel is that yo might inadvertantly syphone off some 'good' fuel. I'm sure proper monitoring of the one good tank will catch this?

[Meikleour]

PENKO: A point not often appreciated by crew is that the fuel pumps deliver flow at a high pressure however the actual flow rate is restricted by the physical pipework - once there is a split in that pipework (as in the Air Transat case ) then the allowed flow of fuel can be dramatically larger than normal. IIRC with the AT A330 usual 2-eng burn was c. 6tons/hr. Once they opened the crossfeed the flowrate went up to 25tons/hr!!! Yes thats correct. So the fuel from the `good`side tank was squandered very quickly indeed. My reference to the A330 fuel loss (non specified area) was that the pumps should have been switched off to see if either engine would flame-out! Hence my simpathy for the crew`s reaction.

Your point about monitoring and being prepared to rethink any outcomes is valid.