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Fuel Useage Definitions And Relationships  
User currently offlineSunriseValley From Canada, joined Jul 2004, 4800 posts, RR: 5
Posted (5 years 6 months 3 weeks 10 hours ago) and read 11570 times:

What is the relationship for a particular flight segment, between the fuel load ( difference between ZFW and MTOW) "block fuel" and "fuel burn" ?

19 replies: All unread, jump to last
 
User currently offlineDispatchguy From United States of America, joined Jan 2006, 1249 posts, RR: 2
Reply 1, posted (5 years 6 months 3 weeks 8 hours ago) and read 11565 times:

Block fuel is usually the required gate departure fuel, whereas fuel burn is your planned segment burn. Block fuel is the segment burn, alternate, reserve, contingency, etc.


Nobody screws you better than an airline job!
User currently offlineWILCO737 From Greenland, joined Jun 2004, 8967 posts, RR: 76
Reply 2, posted (5 years 6 months 3 weeks 5 hours ago) and read 11544 times:
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Quoting SunriseValley (Thread starter):
difference between ZFW and MTOW

ZFW= Zero fuel weight. As the name says: the weight of the airplane and everyting in it EXCEPT the fuel.

MTOW= Maximum take off weight. The maximum structural allowed take off weight. But there can be a MATOW (max allowable take off weight, basically a performance limited take off weight, due to short runway, high elevation, wet or snow on the runway, 2nd segment climb limited etc etc. This is lower than the structural possible take off weight.

Block fuel: Total fuel on board including trip fuel, contingency fuel, alternate fuel, final reserve, (maybe extra fuel) and taxi fuel. Basically the fuel you have on board right before pushback.

Fuel burn: we call it trip fuel. the fuel you need from brake release at the departure airport to the destination airport.

WILCO737 (MD11F)
 airplane 



It it's not Boeing, I am not going.
User currently offlineSunriseValley From Canada, joined Jul 2004, 4800 posts, RR: 5
Reply 3, posted (5 years 6 months 2 weeks 6 days 16 hours ago) and read 11491 times:



Quoting WILCO737 (Reply 2):
Block fuel: Total fuel on board including trip fuel, contingency fuel, alternate fuel, final reserve, (maybe extra fuel) and taxi fuel. Basically the fuel you have on board right before pushback.

So why would this value differ , except for taxi fuel, ( if it does) from the difference between ZFW and MTOW/ MATOW . Is there some generally accepted standard for the amount of fuel that should be remaining in the tanks when the engines shut down at the gate.


User currently offlinePhilSquares From , joined Dec 1969, posts, RR:
Reply 4, posted (5 years 6 months 2 weeks 6 days 15 hours ago) and read 11490 times:



Quoting SunriseValley (Reply 3):
So why would this value differ , except for taxi fuel, ( if it does) from the difference between ZFW and MTOW/ MATOW . Is there some generally accepted standard for the amount of fuel that should be remaining in the tanks when the engines shut down at the gate.

MTOW is the structural limit for the particular aircraft. It is composed of the ZFW and the Block Fuel. For example an aircraft might have a ZFW of 100 tons, and a block fuel of 50 tons, it's takeoff weight will be 150 tons. However, it might have a MTOW of 165 tons, allowing for either 15 additional tons of fuel or payload, assuming the MZFW (Max Zero Fuel Weight) will allow that.

There are times when the aircraft can not take off at MTOW due to performance limitations (both take off and landing). So, one situation would be where due to performance limitations, the aircraft only has the performance capability to depart at 150 tons, even though the MTOW would be 165 tons, the MATOW would be 150 tons. This is also know as the field limit weight.

Or there could be a situation where the MLW weight would be exceeded if the additional 15 tons were uplifted either as payload or fuel. In that case the MATOW would be 150 tons, not the 165 tons as per the MTOW.

Hope that helps.


User currently offlineOldAeroGuy From United States of America, joined Dec 2004, 3473 posts, RR: 67
Reply 5, posted (5 years 6 months 2 weeks 6 days 8 hours ago) and read 11440 times:



Quoting SunriseValley (Thread starter):
What is the relationship for a particular flight segment, between the fuel load ( difference between ZFW and MTOW) "block fuel" and "fuel burn" ?

"Block Fuel" is defined as the total fuel burned from engine start at the beginning of the mission to engine shut down at the end of the mission.

"Fuel Burn" and "Block Fuel" are the same thing.

Quoting WILCO737 (Reply 2):
Block fuel: Total fuel on board including trip fuel, contingency fuel, alternate fuel, final reserve, (maybe extra fuel) and taxi fuel. Basically the fuel you have on board right before pushback.

No, "Block Fuel" is the fuel actually burned on a mission. It is not the total fuel load that you are describing.

Quoting PhilSquares (Reply 4):
MTOW is the structural limit for the particular aircraft. It is composed of the ZFW and the Block Fuel.

Once again, you're describing the fuel load, not the "Block Fuel"

Total Fuel Load = Taxi Out Fuel + Mission Fuel (from runway entry at takeoff to runway exit on landing) + Reserve Fuel

Reserve Fuel includes missed approach, flight to alternate and approach at alternate as well as contingency fuel for holding, higher than forecast winds, ETOPS critical fuel scenario diversion etc.

Note that there is no allowance for Taxi In Fuel in Total Fuel as some of the Reserve Fuel can be used.

Block Fuel = Taxi Out Fuel + Mission Fuel + Taxi In Fuel

Takeoff Weight = ZFW + Mission Fuel + Reserve Fuel

Start of Taxi Weight = ZFW + Taxi Out Fuel + Mission Fuel + Reserve Fuel

Now, let's assume a mission is operating on the MTOW line of the Payload - Range curve:

MTOW = ZFW + Mission Fuel + Reserve Fuel

Start of Taxi Weight = MTOW + Taxi Out Fuel

and there is a Max. Taxi Weight defined structural consideration usually defined by:

Max. Taxi Weight = MTOW + Taxi Out Fuel Allowance



Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
User currently offlineWILCO737 From Greenland, joined Jun 2004, 8967 posts, RR: 76
Reply 6, posted (5 years 6 months 2 weeks 6 days 4 hours ago) and read 11417 times:
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Quoting OldAeroGuy (Reply 5):

No, "Block Fuel" is the fuel actually burned on a mission. It is not the total fuel load that you are describing.

I always order Block fuel on all my flights and that includes: Trip fuel, cont fuel, alternate fuel, final reserve fuel, (maybe extra fuel) and taxi fuel.

Mission Fuel? never heard of that term. We don't use that. Maybe your "mission fuel" is the real "trip fuel". THe fuel you need from departure to destination.

WILCO737 (MD11F)
  

[Edited 2008-12-23 00:50:16]


It it's not Boeing, I am not going.
User currently offlineWILCO737 From Greenland, joined Jun 2004, 8967 posts, RR: 76
Reply 7, posted (5 years 6 months 2 weeks 6 days 4 hours ago) and read 11411 times:
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Here the fuel figures for one of my flights from last month: (these are real original figures how I see it on ALL my flight plans for EVERY flight)

Big version: Width: 1024 Height: 683 File size: 153kb


There you can see: trip, cont. 5PC, ALTN, FINRES, CRIT, PLNTOF, EXTRA, TOF, TAXI, BLOCK.

Block fuel at the bottom, add all the fuel figures from above and you get the block fuel. So the fuel I have on board before pushback.

WILCO737 (MD11F)
 airplane 



It it's not Boeing, I am not going.
User currently offlineBellerophon From United Kingdom, joined May 2002, 583 posts, RR: 59
Reply 8, posted (5 years 6 months 2 weeks 6 days ago) and read 11389 times:

OldAeroGuy

..."Block Fuel" is defined as the total fuel burned from engine start at the beginning of the mission to engine shut down at the end of the mission...

Block Fuel is not a term I have seen formally defined, as we have never used it in my EU airline, but I am surprised to read your definition of it. I had always thought, as others have said, that it did mean the total fuel on board immediately prior to taxy out.

Your definition of Reserve Fuel is, I must assume, a US definition, as it completely unrecognisable to those operating under JAA/EU flight planning rules, where Reserve Fuel is defined as the minimum fuel required to be remaining in tanks, at normal landing, and is calculated as 30 mins holding, at 1,500 ft, at planned landing weight.

Reserve Fuel is an important figure under JAA/EU ops, because if, for any reason, at any time, a JAA/EU operator's aircraft calculates it will land with less than Reserve Fuel remaining in tanks, an emergency must immediately be declared.

Our fuel flight plans look exactly similar to that shown by WILCO737 with the exception that we use the term REQUIRED FUEL to denote the total fuel on board at start up.

Best Regards

Bellerophon


User currently offlineOldAeroGuy From United States of America, joined Dec 2004, 3473 posts, RR: 67
Reply 9, posted (5 years 6 months 2 weeks 5 days 19 hours ago) and read 11359 times:

Definitions are the key to the answers for this thread. The ones I've been using are more or less consistent with those used by the Airline Transport Association (ATA) as described in this link:

http://adg.stanford.edu/aa241/cost/atamethod.html

Quoting WILCO737 (Reply 6):
I always order Block fuel on all my flights and that includes: Trip fuel, cont fuel, alternate fuel, final reserve fuel, (maybe extra fuel) and taxi fuel.

Note that the ATA definition for Block Fuel does not include contingency, alternate, final reserve, or extra fuel for the wife and kids.

Quoting Bellerophon (Reply 8):
Your definition of Reserve Fuel is, I must assume, a US definition, as it completely unrecognisable to those operating under JAA/EU flight planning rules, where Reserve Fuel is defined as the minimum fuel required to be remaining in tanks, at normal landing, and is calculated as 30 mins holding, at 1,500 ft, at planned landing weight.

There are many ways of defining reserve fuel. Individual airlines often have their own definitions and requirements. The regulatory definitions are minimum amounts.

Please see the link for the ATA's definition of Domestic and International Reserve Fuel. It results in more fuel at landing than JAA/EU or FAA minimum reserves.



Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
User currently offlineWILCO737 From Greenland, joined Jun 2004, 8967 posts, RR: 76
Reply 10, posted (5 years 6 months 2 weeks 5 days 19 hours ago) and read 11356 times:
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Quoting OldAeroGuy (Reply 9):
Airline Transport Association (ATA)

It is the one for America. Doesn't mean that everybody uses these terms. Here it is called Block fuel.

WILCO737 (MD11F)
 airplane 



It it's not Boeing, I am not going.
User currently offlineOldAeroGuy From United States of America, joined Dec 2004, 3473 posts, RR: 67
Reply 11, posted (5 years 6 months 2 weeks 5 days 19 hours ago) and read 11343 times:



Quoting WILCO737 (Reply 10):
It is the one for America. Doesn't mean that everybody uses these terms. Here it is called Block fuel.

As I said, it's all in the definitions. And the differences are not just in America. As Bellerophon said, your Block Fuel is his Required Fuel. I believe that he operates out of the UK based on his User Info.

Quoting Bellerophon (Reply 8):
Our fuel flight plans look exactly similar to that shown by WILCO737 with the exception that we use the term REQUIRED FUEL to denote the total fuel on board at start up.




Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
User currently offlinePhilSquares From , joined Dec 1969, posts, RR:
Reply 12, posted (5 years 6 months 2 weeks 5 days 17 hours ago) and read 11330 times:



Quoting OldAeroGuy (Reply 9):
Note that the ATA definition for Block Fuel does not include contingency, alternate, final reserve, or extra fuel for the wife and kids.

EVERY airline has their own definitions. ATA is a meaningless organization when it comes to the operations side of airlines.

Quoting OldAeroGuy (Reply 5):
Quoting PhilSquares (Reply 4):
MTOW is the structural limit for the particular aircraft. It is composed of the ZFW and the Block Fuel.

Once again, you're describing the fuel load, not the "Block Fuel"

I disagree! Every airline I have been associated with uses the term "block fuel" to mean the required fuel load. The fuel burn is just that, fuel burn or segment fuel, not block fuel! Again, by definition, most airlines will call that "trip fuel".


User currently offlineSunriseValley From Canada, joined Jul 2004, 4800 posts, RR: 5
Reply 13, posted (5 years 6 months 2 weeks 5 days ago) and read 11277 times:



Quoting Bellerophon (Reply 8):
where Reserve Fuel is defined as the minimum fuel required to be remaining in tanks, at normal landing, and is calculated as 30 mins holding, at 1,500 ft, at planned landing weight.

Apparently most operators have their own rules , some of which could be greater than the minimum required by the regulator in their jurisdiction . I would like some idea what this value , or value range, might be . Phil , what does it translate into for types that you have flown, ? I would ask the same question of Wilco737 and Bellerophon and any other pilot or dispatcher monitoring this thread.


User currently offlineTristarSteve From Sweden, joined Nov 2005, 3970 posts, RR: 34
Reply 14, posted (5 years 6 months 2 weeks 5 days ago) and read 11272 times:

With this discussion on Block fuel , you can see why when I am refuelling an aircraft, I get the fuel figure, write it down, then show it to the pilot and ask if this is the Fuel In Tanks reqd.
You must make sure he hasn't given you the Take off fuel (without the taxy).

Quoting SunriseValley (Reply 13):
Apparently most operators have their own rules , some of which could be greater than the minimum required by the regulator in their jurisdiction

There is a constant battle in the airline between the Ops Managers who are trying to reduce the reserves to the legal minimum, and the pilots who want more. It is never ending. They come out with ideas like En-route alternates, and in-flight replanning, and the pilots always find a good reason to take more than flight plan.


User currently offlineTristarSteve From Sweden, joined Nov 2005, 3970 posts, RR: 34
Reply 15, posted (5 years 6 months 2 weeks 4 days 22 hours ago) and read 11261 times:



Quoting PhilSquares (Reply 12):
Every airline I have been associated with uses the term "block fuel" to mean the required fuel load.

I agree. Block fuel is fuel when you are off-blocks (or chocks).
It seems that in the USA block fuel is fuel used from off-blocks to on-blocks, but this includes taxy in fuel?


User currently offlineOldAeroGuy From United States of America, joined Dec 2004, 3473 posts, RR: 67
Reply 16, posted (5 years 6 months 2 weeks 4 days 20 hours ago) and read 11251 times:

Quoting PhilSquares (Reply 12):
I disagree! Every airline I have been associated with uses the term "block fuel" to mean the required fuel load.

What's your definition of Block Time? Block Fuel and Block Fuel go hand in hand.

The US Department of Transportation defines Block Time as:

"The cost of aircraft block (taxi plus airborne) time..."

http://www.airlines.org/economics/specialtopics/ATC+Delay+Cost.htm

From Block to Block, two of the consumables you're using are Time and Fuel.

Please see the paragraph at the beginning of page 282 in this link:

http://books.google.com/books?id=Jgp...esult&resnum=1&ct=result#PPA282,M1

It defines Block Time as the time between engine start at the origin airport and engine stop at the destination airport and Block Fuel as the fuel used between these events.

The referenced book is published by the Cambridge University Press, indicating that this definition of Block Time and Block Fuel is not restricted to the US.

Quoting PhilSquares (Reply 12):
ATA is a meaningless organization when it comes to the operations side of airlines.

US airlines are the primary members of the ATA, just as the IATA have international airlines as primary members. Both ATA and IATA are hardly meaningless when it comes to airlines operations.

Quoting TristarSteve (Reply 15):
It seems that in the USA block fuel is fuel used from off-blocks to on-blocks, but this includes taxy in fuel?

Yes

Quoting OldAeroGuy (Reply 5):
Block Fuel = Taxi Out Fuel + Mission Fuel + Taxi In Fuel


[Edited 2008-12-24 09:26:57]

[Edited 2008-12-24 09:43:27]


Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
User currently offlinePhilSquares From , joined Dec 1969, posts, RR:
Reply 17, posted (5 years 6 months 2 weeks 4 days 13 hours ago) and read 11224 times:



Quoting OldAeroGuy (Reply 16):
The US Department of Transportation defines Block Time as:

That's great, but there are other parts of the world that don't come under the DOT. ATA is a lobbying organization. Nothing more nothing less. To put IATA in the same sentence with the ATA is a joke!!!

And block fuel does not include taxi fuel. I know of no major airline in the US that includes taxi fuel in block fuel! The normal terms used are taxi fuel, trip fuel. It's much more precise and amazingly more clear that way. In addition, airlines can tailor taxi fuel to specific airports.


User currently offlineOldAeroGuy From United States of America, joined Dec 2004, 3473 posts, RR: 67
Reply 18, posted (5 years 6 months 2 weeks 4 days 11 hours ago) and read 11218 times:



Quoting PhilSquares (Reply 17):
Quoting OldAeroGuy (Reply 16):
The US Department of Transportation defines Block Time as:

That's great, but there are other parts of the world that don't come under the DOT

How do you or your airline define Block Time?



Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
User currently offlinePhilSquares From , joined Dec 1969, posts, RR:
Reply 19, posted (5 years 6 months 2 weeks 4 days 1 hour ago) and read 11171 times:



Quoting OldAeroGuy (Reply 18):
How do you or your airline define Block Time?

This discussion isn't about block time, it's about fuel! So, what my airline does is meaningless in this discussion since it's about fuel.


The problem with your definition of block fuel is you fail to take into account Taxi fuel is actually composed of STTO (start, taxi take off fuel). The take off fuel is the fuel used from application of take off thrust to the end of clean up. From that point on, the block fuel would be accurate. So, block fuel and block time do not necessarily go hand in hand.


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