Single Engine Fuel Jettison

[Tyrion 2]

Hello,

 

First of all, yes, I used the search function on this forum, and yes, I searched through both FCOM's, the FCTM and the QRH.

That said, I still don't have an answer for the following situation:

 

Tonight, I was testing the 777 (using the freighter version).

I was all set up for a long flight at high load, but ran into a (programmed...) severe engine failure shortly after liftoff.

 

My first priority was to keep flying the aircraft. No particular problem, despite the alarms and sudden loss of thrust on the left side.

Once I got everything under control, I went through the appropriate checklist on the ECL. So far, so good.

 

Now, my plan was to land back at my departure airport, but to do so, I had to jettison about 80000kgs of fuel. I entered a hold over the sea to do just that.

The problem I ran into here, is that with only one engine operating, dumping fuel caused a quickly escalating fuel imbalance,

and no matter what I tried, I couldn't get it to stabilize.

 

By the time the center tank was empty, the imbalance had reached about 3500kg. Roughly what could be expected without cross feeding. I kept the fuel jettison going for a while to see whether the auto jettison function would turn off the right jettison pump when the right main tank (the less full one) reached jettison goal/2 (which it didn't). No idea whether it should stop here though, it was just an idea I had while flying so I tested it.

 

a couple of notes:

1) fuel jettison with 2 engines running seemed to be working perfectly fine in a previous test flight.

2) cross feed also worked perfectly when fuel wasn't being jettisoned.

 

As it was, I manually stopped the fuel jettison a bit early, and then kept flying in the hold while cross feeding to  reduce the imbalance a bit, before landing.

 

Anyway, what I'm looking for:

What would be the correct procedure in this case? What went/did I do wrong?

 

Feel free to reply with references to the correct sections in the manuals... I didn't find what I was looking for so far...

 

Thanks in advance...

[FLEX1978 373]

"The primary purpose of fuel balance limitations on Boeing aircraft is for structural life of the airframe and not for controllability limitations."

"Lateral control is not significantly affected when operating with fuel beyond normal balance limits."

"The primary purpose for fuel balance alerts are to inform the crew that imbalances beyond the current state may result in increased trim drag and higher fuel consumption.

 

 

So...  Crossfeed & don't worry about an imbalance unless you suspect a leak. You have an engine failure, focus on getting down to MLW or performing an overweight landing ASAP

 

Hanging around in the hold single engine  just to get  the tanks all neat and tidy would get you fired

 

 

[nawarren 83]

Hi,

 

I made a similar post to this a long time ago, there is a thread somewhere in this forum. I think the problem I had was that the APU was being fed by the left pump and with engine shut down it led to a fuel imbalance and I could not figure out how to resolve it. Not sure what correct logic should be on real A/C. But I was surprised if this was real behaviour, as it seemed wrong to me.

 

Cheers

 

Neil

[FLEX1978 373]

Hi,

 

I made a similar post to this a long time ago, there is a thread somewhere in this forum. I think the problem I had was that the APU was being fed by the left pump and with engine shut down it led to a fuel imbalance and I could not figure out how to resolve it. Not sure what correct logic should be on real A/C. But I was surprised if this was real behaviour, as it seemed wrong to me.

 

Cheers

 

Neil

Read the above post. Also the APU uses a small amount of fuel, you would have to spend hours in the hold before seeing a major imbalance.  As mentioned above, just land the damn thing. A fuel imbalance (large or small) is minor unless related to a leak. It does not affect the safety of the flight, only additional fuel burn from drag.

[nawarren 83]

Hi Rob,

 

The problem with the APU is not the amount of fuel it burns, but that to correct a fuel imbalance from left to right side you need to turn off the left hand pumps, which you can do. However with APU running it automatically uses left pump, so pump stays on, imbalance gets worse!!

 

 

 

Cheers

 

Neil

[FLEX1978 373]

Hi Rob,

 

The problem with the APU is not the amount of fuel it burns, but that to correct a fuel imbalance from left to right side you need to turn off the left hand pumps, which you can do. However with APU running it automatically uses left pump, so pump stays on, imbalance gets worse!!

 

 

 

Cheers

 

Neil

 

 

Ok, but once again.. Fuel imbalance is not a limitation. You have an engine failure, prioritize and land the aircraft! The 777 can happily land  with any imbalance. 

[Tyrion 2]

Thanks for the input Rob! Indeed, landing the aircraft at MLW with about 3000kg imbalance proved to be no problem.

Handling the thrust asymmetry was much more of a handful. ^_^

 

Still wondering about this situation, but I'll live.

[77west 139]

way back I was playing around with failures and ended up with more than 10,000kg imbalance, hardly noticed it at all.

[tcas_climb 45]

So with sp1 we still can't feed the right engine off the left tank with the left engine off and the APU running?

[Tyrion 2]

So with sp1 we still can't feed the right engine off the left tank with the left engine off and the APU running?

 

Yes you can... I had no problems with feeding the right engine of the left tank with the APU running.

 

It's just when I added fuel jettison in the mix, that I got results which I didn't expect. (But that may be more to do with a lack of knowledge on my part than anything else)