iwok
Topic Author
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Fuel Burn As A Function Of Fuel Consumption 777-LR

Fri Jan 11, 2013 12:32 am

folks,

I am wonder how fuel burn changes for a 777-LR as it consumes fuel over the course of a long flight.

Assuming it takes of at MTOW how does the fuel usage change.

I am not sure how to find this and I've done a search but found nothing.

Your help is appreciated!

iwok
 
sunrisevalley
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RE: Fuel Burn As A Function Of Fuel Consumption 777-LR

Fri Jan 11, 2013 7:37 pm

From a flight plan , 16hr flight at about MTOW ; Burn at cruise for the first hour was ~8t and for the last hour ~5.6t.
 
iwok
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RE: Fuel Burn As A Function Of Fuel Consumption 777-LR

Fri Jan 11, 2013 8:59 pm

Quoting sunrisevalley (Reply 1):

From a flight plan , 16hr flight at about MTOW ; Burn at cruise for the first hour was ~8t and for the last hour ~5.6t.

Thanks very much! That really helps me a lot.

That's a long flight!

iwok
 
sunrisevalley
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RE: Fuel Burn As A Function Of Fuel Consumption 777-LR

Fri Jan 11, 2013 9:48 pm

Quoting iwok (Reply 2):
That's a long flight!

A hypothetical ORD-AKL .
 
DFWHeavy
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RE: Fuel Burn As A Function Of Fuel Consumption 777-LR

Fri Jan 11, 2013 10:10 pm

I'm surprised there isn't a bigger difference between the hourly burn rate from the beginning to the end.
Christopher W Slovacek
 
sunrisevalley
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RE: Fuel Burn As A Function Of Fuel Consumption 777-LR

Fri Jan 11, 2013 10:35 pm

[

Quoting DFWHeavy (Reply 4):
I'm surprised there isn't a bigger difference between the hourly burn rate from the beginning to the end.

The full story, Total fuel load incl. reserves 131.3t ; total fuel burn 110.593t ; total cruise burn 100.171t
 
DFWHeavy
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RE: Fuel Burn As A Function Of Fuel Consumption 777-LR

Fri Jan 11, 2013 10:47 pm

Is landing with ~40,000 lbs of fuel the norm on a 777? Seems like quite a bit, but perhaps not not so with holding and diversion fuel. This particular circumstancehas about 3 hours of fly time remaining based on landing fuel.
Christopher W Slovacek
 
sunrisevalley
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RE: Fuel Burn As A Function Of Fuel Consumption 777-LR

Sat Jan 12, 2013 12:17 am

Quoting DFWHeavy (Reply 6):
Is landing with ~40,000 lbs of fuel the norm on a 777?

I am not sure what typical mission rules are . In this instance the 5% contingency (48min./5504kg) is a function of the distance flown. Then there is the fuel to reach the alternate which in this case was CHC ( 58min/ 9729kg) and hold plus final reserve (45min/ 5494 kg). I am sure that there are persons on this list qualified to comment.
 
prebennorholm
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RE: Fuel Burn As A Function Of Fuel Consumption 777-LR

Sat Jan 12, 2013 3:42 am

Quoting sunrisevalley (Reply 1):
Burn at cruise for the first hour was ~8t and for the last hour ~5.6t.

= 113.33 kg/min for average of first and last hour. Last hour = 93.33 kg/min.

Quoting sunrisevalley (Reply 7):
5% contingency (48min./5504kg)

= 114.66 kg/min. In line with 113.33 above.

Quoting sunrisevalley (Reply 7):
to reach the alternate which in this case was CHC ( 58min/ 9729kg)

= 167.24 kg/min. Much more than last hour cruise burn. Here some low altitude flight and climb profile must be in the calculation.

Quoting sunrisevalley (Reply 7):
hold plus final reserve (45min/ 5494 kg)

= 122.09 kg/min. And here some low altitude flying.

So after an eventless flight with zero wind component it lands with 45,694 lbs.

I have no specific knowledge about those calculations. Are my assumptions correct?
Always keep your number of landings equal to your number of take-offs
 
sunrisevalley
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RE: Fuel Burn As A Function Of Fuel Consumption 777-LR

Sat Jan 12, 2013 12:33 pm

Quoting prebennorholm (Reply 8):
I have no specific knowledge about those calculations. Are my assumptions correct?

Your assumptions are probably correct. Really you need an airline pilot to comment .
 
mandala499
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RE: Fuel Burn As A Function Of Fuel Consumption 777-LR

Mon Jan 14, 2013 5:16 am

If you want it cheaper in fuel, you can dispatch to Fiji, with AKL as 1st alternate, and CHC as your last alternate, and carry fuel enough to divert from Fiji to CHC.... that way you can save on the 5% contingency (You carry 5% to Fiji not AKL). Cheaper and still legal, and... still safe. Although, this is an oversimplified way of explaining it.

Mandala499
When losing situational awareness, pray Cumulus Granitus isn't nearby !
 
sunrisevalley
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RE: Fuel Burn As A Function Of Fuel Consumption 777-LR

Sun Jan 20, 2013 3:48 pm

Quoting mandala499 (Reply 10):
If you want it cheaper in fuel, you can dispatch to Fiji, with AKL as 1st alternate, and CHC as your last alternate, and carry fuel enough to divert from Fiji to CHC.... that way you can save on the 5% contingency (You carry 5% to Fiji not AKL). Cheaper and still legal, and... still safe. Although, this is an oversimplified way of explaining it.

Mandala499

Looking at the flight plan , if I am reading it right, it would have saved about 1t in contingency fuel.
 
WingedMigrator
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RE: Fuel Burn As A Function Of Fuel Consumption 777-LR

Mon Jan 21, 2013 4:34 am

Quoting sunrisevalley (Reply 11):
it would have saved about 1t in contingency fuel

1t = 10 more passengers
 
mandala499
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RE: Fuel Burn As A Function Of Fuel Consumption 777-LR

Mon Jan 21, 2013 5:06 am

Quoting sunrisevalley (Reply 11):
Looking at the flight plan , if I am reading it right, it would have saved about 1t in contingency fuel.

What ZFW are we looking at here?
When losing situational awareness, pray Cumulus Granitus isn't nearby !
 
sunrisevalley
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RE: Fuel Burn As A Function Of Fuel Consumption 777-LR

Mon Jan 21, 2013 1:48 pm

Quoting mandala499 (Reply 13):
What ZFW are we looking at here?

198t.
 
mandala499
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RE: Fuel Burn As A Function Of Fuel Consumption 777-LR

Mon Jan 21, 2013 8:23 pm

Yes, I just did a quick calculation using ORD-PPG-AKL-CHC as the routing with PPG as dispatch destination and CHC as the final alternate, yes, saves about 1 ton of contingency fuel... Do that route daily, and you'd be saving 2 tonnes a day which gives it 730 tons a year. That's in contingency fuel savings alone.

Assume that means you land with 1 ton less fuel, how much fuel do you save for the whole trip by not carrying that one ton of contingency fuel? About 230kgs... that translates to 170 tons a year.

So now you save 1000 tons. Where I am, that means over 1 million dollars a year saved.

Is safety compromised? Well, you're still able to go to Christchurch and still have over 2h13mins worth of holding and save 1 million dollars a year... otherwise, you don't save the 1 million dollars and land with 2h22 mins worth of holding.

Unfortunately, there isn't much "eeking out every cent" in terms of dispatch creativity on ORD-AKL, but AKL-ORD am sure there are ways to save more... eg: dispatch as AKL-XXX-ORD, with YYY as a final alternate, but find XXX that would give the fuel remaining at ORD the equivalent of diverting from ORD to YYY and still have a 45min holding.

There's another method of using the destination as a final alternate + X mins holding, eg: AKL-XXX with ORD as destination, and upon getting near XXX, the aircraft would check if the conditions at ORD is good enough to go there with only enough fuel to go to another airport near ORD, but have certain requirements such as it can only be done if conditions at ORD is better than a certain minimum weather requirement, and have at least a second parallel runway to the expected runway. I think QF does this method but I cannot remember the rules clearly for this.
When losing situational awareness, pray Cumulus Granitus isn't nearby !
 
sunrisevalley
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RE: Fuel Burn As A Function Of Fuel Consumption 777-LR

Tue Jan 22, 2013 12:41 pm

Quoting mandala499 (Reply 15):
Yes, I just did a quick calculation using ORD-PPG-AKL-CHC as the routing with PPG as dispatch destination and CHC as the final alternate, yes, saves about 1 ton of contingency fuel... Do that route daily, and you'd be saving 2 tonnes a day which gives it 730 tons a year. That's in contingency fuel savings alone.

Very interesting ! Are these some of the tricks of being a despatcher to eek out savings but still comply with the rules ?
 
mandala499
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RE: Fuel Burn As A Function Of Fuel Consumption 777-LR

Tue Jan 22, 2013 4:42 pm

Quoting sunrisevalley (Reply 16):
Are these some of the tricks of being a despatcher to eek out savings but still comply with the rules ?

Yes, subject to regulatory approvals though. If your regulators approve it, do it, if not... tough luck. The reason why this is possible these days is because of the accuracy in flight planning, predicted winds and temperatures.

Quoting iwok (Thread starter):
I am wonder how fuel burn changes for a 777-LR as it consumes fuel over the course of a long flight.

Just to give an idea... Holding is much slower than the cruise speeds... but... at 35,000ft... at 320tons gross weight holding would give you 9950kgs/hour, at 260 tons it's 7250kgs/hour at 200tons it's 5350kgs/hour...

Mandala499
When losing situational awareness, pray Cumulus Granitus isn't nearby !

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