A320 when to use fuel gravity feed QRH?

[Mooneyboy]

Hello all,

Just wondering if anyone could clarify this for me:

If you loose both fuel pumps in say the left wing the ECAM will direct you to open the cross feed (as long as there is no leak) in order to provide both engines with fuel under positive pressure. Let's say you had only just levelled off at FL320 when you had the double pump loss. The FCOM says to use the gravity procedure when the fuel in that tank is required. So am I right in thinking let's say you have an extra 800kg of fuel on top of your trip+altn+final reserve (i.e 800+ on plog fuel) you could burn this off without the need to descend to gravity ceiling and then when you get down to your plog fuel, gravity feed the left side either descending to gravity feed ceiling or maintaining level depending on elapsed time?

Basically when is your fuel required considering your continuing to your planned destination and are there any potential pitfalls or gotchas to the scenario above?

Many thanks.

[whitelabel]

I discussed this scenario once with a trainer and I think it shows good airmanship to consider it.

You need the 30 mins above FL300 to get rid of the cavitation but after that you can do gravity feeding. Just realise that you will create an imbalance of about 1200+ kg and that when you arrive at destination you could end up with only a few hundered kilo's on the positive pressure side. Depending of course on how much extra you took.

[Mooneyboy]

Thanks whitelabel,

In terms of FCOM limitations it would be fine to exceed them as its a failure in the fuel system so a 1200 imbalance should be ok and controllable. So let's say you aim to arrive at your destination with 2T. Normally you would arrive with 1T either side so if you generated a 1200 imbalance in the cruise you could be in the situation of re opening the cross feed in order not to run one side empty.

So from this situation I guess the worst out come would be to carry on to destination do an approach with the cross feed closed as directed by the gravity QRH forget about the cross feed then flameout on one engine with the remaining side been fed only by gravity.

So to me it seems that unless I got a fair bit of extra fuel it would be safest option to divert.

[vilas]

Mooneyboy
Is it necessary to do all that? From PER G 2/4 IN CRUISE QUICK CHECK for a 1000nm distance if you descend to FL300 from FL320 you will see that you burn extra 310kgs. You have extra 800kgs. so you will still have 490kgs extra. Just descend to FL300 keep the cross feed off and carry on.

[Mooneyboy]

Thanks villas,

Your right that would be a more straight forward path. At least then your focus will be just on the extra fuel burnt and not on potential pitfalls of not monitoring a fuel imbalance correctly.

Looked through a few potential scenarios the other day inflight. Think you would be having a bad day to have it top of climb at FL390 on a long flight with little extra fuel. Although knowing the sim I'm sure with other events thrown in would make an interesting sim.

Thanks for all your help.