[stevepeg]

A320/330/340/350 driver here (can't get away from Airbus apparently).

Nope, there is no system to confirm a leak apart from a camera around the tail if you're lucky enough to have one, my previous airline had a flight where an engine leak was detected this way. Think about it, how would you design such a system? So this falls on the crew.

The procedure to determine if you have a leak is pretty much the same across types: add the fuel on board (FOB) to the fuel used (FU) and make sure that the number you get is the same as what you started the flight with. If it's less by some margin then you probably have a leak. You can confirm further by looking at tank quantities (but they take time to reduce depending on the size of the hole). If you get an engine or pylon leak then you might also see increased fuel flow on that engine. If the leak is elsewhere in the system then you might notice a smell. If you can't work it out then the procedure (at least on Airbus types) usually involves turning an engine off to see if the leak stops (yep, really).

As for the ECAM "open fuel transfer valves" message, I don't know for sure on the 380 but all the other Airbus types I've flown have something like:

.IF NO FUEL LEAK

FUEL IMBALANCE....MONITOR

So it doesn't really instruct you to open the transfer valves but leads you into the fuel imbalance procedure if you think you need it. The very first line of the fuel imbalance procedure says something like "Don't apply this procedure if fuel leak is suspected".

[mannykannot]

Thank you for bringing your expertise here. I was wondering if you could give some insight on something that occurred to me while reading this: at first sight, transferring fuel to the leaking tanks might seem to be a substitute for the failure of the fuel jettison system, while also doing something about the increasing lateral imbalance.

[stevepeg]

That’s good lateral thinking :)

Given that the aircraft can be landed over max landing weight (needs a maintenance inspection) and is still controllable with total imbalance I’d say that balancing just wasn’t as pressing of a concern.

Also, with that much damage you never really know where else it could be leaking. Leaking fuel into critical spaces of the aircraft could be bad so turning on the fuel crossfeed might add extra issues.

[SkyPuncher]

You could absolutely design a system that could detect a leak. I’m guessing that it’s just not common enough, or at least catastrophically common enough, to warrant.

At its simplest you measure estimated volume delivered to the engines against estimated volume remaining in the tank. Both are things that should be digitally measurable.

The problem seems to be that the only case it really matters is in a catastrophic accident where such measurements are going to be broken anyways.

[stevepeg]

It’s a good idea, some aircraft have quite complex fuel systems though so it would have to account for fuel moving between tanks.

E.g. the A330 has an inner tank in each wing (which itself can be split into two compartments if damaged), an outer tank in each wing and fuel in the horizontal stabiliser which is used for CG control in the cruise. All of that plumbing can leak too. You’d be adding significant weight and complexity implementing leak detection across all that.

Regardless of all of this, the aircraft is still fully controllable even with a total asymmetry (one side empty the other full) so balancing the tanks isn’t a massive priority.

[SkyPuncher]

All of that only adds complexity in the calculation, not the measurement.

The engines have predictable fuel consumption patterns. Even if fuel move across a bunch of tanks, you can still calculate total onboard fuels and detect a leak.

[stevepeg]

That’s what it already does though. We get a total fuel figure in the flight deck (FOB) and a figure for how much the engines have used (FU - measures flow in the pylons). Add the two together and if the resulting number isn’t what the flight started with then there’s a leak.

The challenge is knowing where the leak is.