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Finzolas
5th Mar 2009, 08:50
Dear All,

I here again request your help. This time it deals with fuel tankering.

In my company, (737classic operator), we calculate a recommendation about fuel tankering for each flight (mentioned in the flight plan delivered to crews).

The problem is that it only takes account of fuel price differences between the two planned stations (departure and arrival) and the extra fuel burn (associated to the extra fuel carried).
Even though, it is most of the time a loss. No extra fuel should be carried.

Time to time, it is a gain but no credit is taken into account for heavier take off and landing weights.
Further more, if you carry 6t of extra fuel on a 3h flight sector, you may not have the same optimum vertical flight path... the economy is then worse than the one calculated (and it is not definitively an environment friendly practice).

To carry extra fuel may lead also to other problems (wing icing on ground after landing…), even if it is a rare event on 737Classic.

Without considering impact on commercial load, let's take an example: 50€ gain per ton of extra fuel carried... and you carry 6t of extra fuel. This represents 300€... Almost nothing compared to the overall operation cost. (the 50€ gain is calculated for the 1st extra ton, so carry the 2nd is less than 50€ gain and the 3rd even less...).

People justify fuel tankering because:
1/ you cannot evaluate precisely the impact of the other parameters (heavier weights...) so we should not take consideration of it.
2/ the theoretical Gain x Number of annual sectors when you can "earn" (even if it is a reduced number of flights) represents a large amount of annual saving...

As you understand, I believe it is an erroneous analysis.
I strongly believe fuel tankering should be considered only when abnormal fuel price differences are encountered or for operational reasons. I have asked Boeing help to complete the study but they have no data to carry out such calculation.

Could someone share their practice and the reasons behind?

(we used to say that below a 15€ gain, we do not carry extra fuel. This is a value I am not comfortable with neither because I cannot solve an equation to come out to that result).

In advance, thank you!

Fin

BOAC
5th Mar 2009, 10:10
It is a fairly inexact science, and the factors taken into account in the decision WILL in general reflect the degraded performance due to the extra weight. They probably do NOT allow for ATC rouite changes, if any, at the lower achievable levels, but I am sure they are pretty reliable overall. Wing icing is normally covered by Captain's discretion on tanking, as are runway conditions at destination.

Henry VIII
5th Mar 2009, 10:25
Companies should be able to include many of the terms you referred e.g. lower derate in TO, higher brakes gear wearing, etc.
Avoiding fire brigade for a refuelling with pax on board could compensate the fuel penalty to carry on unadvantageus extra fuel as like as deicing requirement in some destination environment could revert a positive tankering into a loss.
As BOAC told "It is a fairly inexact science".

vipero
5th Mar 2009, 10:44
As far as I'm concerned, the fuel tankering analysis are included to avoid unnecessarily extra fuel taken from crews, showing them that 90% of cases it results in a loss of money.

Finzolas
6th Mar 2009, 13:57
My believe is fuel tankering should be done only for operational reasons and not be driven by economic consideration.

One of those situation is positionning flights (no load).
Here you can uplift from the beginning the fuel for the 2 next flights (without having to call for fueller at the next station). You will in this case (if the fuel is cheaper at the first station) uplift much more than 1t.

The indicated information of gain or loss for 1 extra ton is then erroneous as you will extrapole from 1t to 5 or 6 or even more... but the gain is not linear...

Thanks for your contribution

Fin

BelArgUSA
6th Mar 2009, 14:22
My personal experience with fuel tankering, were my years flying ACMI B-707 and DC-8 based in Jeddah for Saudia in the early 1980s... Particularly for the European DC-8 cargo flights to/from Jeddah.
xxx
Operating cargo flights, we were as a rule, always empty, no payload, out of Saudi Arabia. As a matter of fact, I recall having full tanks on all flights to Europe, our only concern were the max landing weight. Fuel reserves, bad weather, low visibility in Europe, we never were concerned, we could hold for hours, and use Amsterdam as Rome alternate...
xxx
The Saudi culture "our jet fuel is cheap" even was common for short local flights, domestic or even international, to gain time, and for convenience. We would load a 707 or DC-8 with sufficient fuel for 3 or 4 stops without refueling for some passenger flights. Shut-down engines nº 1 and 4 for taxi on arrival, that procedure did not exist... What a waste.
xxx
Outside of the aviation subject, I remember buying gasoline for my car, an old Chevrolet Impala in Jeddah. They charged your tank fill-up by "car size" regardless of how many liters you actually bought. A big car, Chevrolet, was 20 Riyals, a small car, i.e. Toyota, was 15 Riyals...
xxx
:rolleyes:
Happy contrails

kijangnim
6th Mar 2009, 15:05
Greetings,

Fuel required is computed in weight, fuel price and delivery is in volume, and the relation is the specific gravity, so fuel price difference has to be corrected with the specific gravity difference.

captjns
6th Mar 2009, 16:43
Fuel tankering has always been cost consideration first. While the price per litre/gallon may be cheaper at your intermediate stop, there is usually a price per litre/gallon from the delivery system into the jet... Thus tankering may be the way to go.

Then there are operational considerations... such as turn times. Some airports charge by the hour for parking. In some instances if you go 1 minute into the next hour... your company gets charged for the full hour. Then there is a matter of downline delays to avoid curfews too.

Alot goes into deciding whether or not to tanker.

wonwinlow
6th Mar 2009, 18:01
Just remember that some serious companies like SIA do their tankering based on fuel "hedging", meaning that they will buy huge amounts of cheap fuel now, to be tankered some time later when prices go up, so all flights leaving SIN for example are tankered to places with expensive fuel prices. They have a very well figured out program for their brake even point.

captjns
7th Mar 2009, 12:57
Very good for SIA... however they were not the first to employ this technique.

Rainboe
7th Mar 2009, 13:15
You do have the option of saving the company money. If it is considered a worthwhile tanking sector, you must consider the maximum fuel you can land with for landing purposes and also ground icing. For a positive sector, yoou should take up to the maximum. It may not be much saving, but you are one flight of many that day that could contribute over a year to a significant saving. It takes a reasonable amount of pragmatism and common sense, but they have given you a figure for guidance. They think it's worth it. They pay your salary. Your job is to do as you are requested by the company, following their guidelines, as long as it's safe and what your flight manager thinks is 'sensible'. If you disagree, you should not just disobey your guidance. You should go in and discuss it with the flight manager to see what you should do. You may well find that if you are not prepared to follow company guidance, you will be invited to leave! They pay you, it is their ball. You do it their way, not yours.

You must always remember far more knowledgeable people than you in the company have worked this out. You should not just ignore guidance- if you disagree, go discuss it with them. There are a lot of other factors involved. Local contracts for a minimum amount of fuel over a period, other fuelling costs, fuel shortages etc. They are not paying you for you to decide you don't want to do it their way!

Finzolas
8th Mar 2009, 18:14
Dear Rainboe,

I absolutely agree with your position.
The thing is I am in charge of reviewing some internal procedures of my company. I am not agains the current ones, I try to improve it, as I am paid for that purpose.

Fuel tankering practice is one of those I concentrate lately because it is a very sensitive subject and because a large amount of money is involved.

As previously mentioned per the collegues, fuel tankering involves more parameters than fuel cost at each planned station and extra fuel burn. Unfortunately, this are the only parameters on which my company base its computation (currently). Other parameters are very hard to take into account, especially automatically. I wondered how other operators solved this, reason of my thread in this forum.

Any suggestion leading to a procedure improvement starts with a strict application of current procedures.

Again, for all of you, thanks for your contribution.

Fin

BOAC
8th Mar 2009, 18:41
The time-honoured 737 Classic 'rule-of-thumb' is 4% per hour. If the computed flight time x 4% is less than the price differential you tank if you can. Take a 3 hour flight: it will cost you 12% of the fuel you tank. If the price at the other end is 15% more than departure, you win. This 'magic' figure is well-proven and takes into account extra burn and lower levels. You need to decide the differential gain at which it becomes non-economical to tank (but as mentioned before, sometimes other factors like turn-round times come into play).

It is fairly easy to write an Excel sheet to do the work for you, but things to remember:

Do not tanker a lot more than you need to return!

Take into account minimum uplifts if any at destinations - some refuellers have a minimum amount rule, so you will finish up paying heavily for 400kg say. Better sometimes to 'undertank'.

Publish the recommended figure on the pilot's plan OR let them work it out from accurate and up-to-date price differentials. They will decide what is 'practical' and should have a feel for how much they need for the return.

If the return is another crew, give the outbound crew the return tank requirement. We've done it for ages this way, and I'm sure it has worked.

hoover1
9th Mar 2009, 00:31
you will burn 10% of your fule just carrying it. so 10% of your extra fuel will be burnt away just for carrying it. we use the rule of thumb that the fuel price needs to be 10% less in order to tanker. our company does this whenever possible. now those who take extra fuel just to make themselves feel better burn away the money saved by those who tanker. so i don't think we ever save money do to others wasting a lot of fuel be it by carrying extra when not needed or flying technique such as decending early and not doing idle decents.

BOAC
9th Mar 2009, 09:35
Finzolasyou will burn 10% of your fule just carrying it. so 10% of your extra fuel will be burnt away just for carrying it. - I suggest you ignore this. A moment's thought shows it to be ludicrous.

RNAV.CAP
9th Mar 2009, 20:01
it depends of course on the aircraft.

jets vs turpo props

CJ Driver
11th Mar 2009, 14:37
Finzolas,

I am slightly surprised that you think this is difficult. For a pilot down trip it is true that the various rules of thumb and back of the envelope calculations make it an inexact science. But since you say that you are involved in the back-office planning for a 737 operator, you presumably have access to all the data you could possibly need to make this a highly exact science.

Assuming you have access to some proper performance based planning tools, you just run the trip plan for every trip based on (1) the intended payload and (2) a payload 1 ton higher. The second trip plan will take a little bit longer and wil cost a little bit more, and the difference is what people are calling the "cost" of tankering a ton of fuel. You can then compare this to the cost of a ton of fuel at the next stop, and immediately see whether it is of benefit to tanker the fuel.

Like all these things it is dependent on having good initial data to get good answers. If you flight planning program incorrectly calculates the true cost of a flight, then you will not get the right answer - but you should probably be fixing that anyway for the sake of the overall operation. And, speaking from personal experience, if you make a mistake on the actual price of fuel at the two locations, you can wipe out the whole benefit in one horrible mistake.

But on the assumption that you are starting with good data, then it can be very satisfying to scrape the odd 50 euros here and there on every sector, and for a busy operator that soon justifies the original investment in the flight planning software, the fuel price database, and the Excel spreadsheet to tell you the answer.

Finzolas
11th Mar 2009, 17:52
CJ Driver,

I believe I am a little bit forward from the situation you describe.

Our flight planning system already computes automatically fuel tankering recommendation based on fuel price differences for the intended stations and cost of tankering.

Even if I assume this is the method used largely in the industry, fuel prices and cost of transport are not the sole parameters to take into account.

If you take into account additional costs (impossible to list al theses but let say heavier take off & landings weights, fuel service, parking fees, delays...), you can reverse the previous recommendation (which was only based on fuel price and cost of transport) and this is in my opinion, tragic.

Most of my colleagues argue that pilot experience will do the rest. I do not give up in building up a tool which helps pilots to take the decision based on a maximum of relevant parameters (we are a charter operator and this does not help)

My English is "not very good looking", sorry for that. I hope my situation is easier to understand now with the additional information I brought above.

Best regards,

Fin

BOAC
11th Mar 2009, 18:04
Fin -your English is fine!

Taking the list you provided (yes, I know it is not all)

heavier take off & landings weights - do you mean the extra wear on brakes and engines, because take-off and landihg fees will NOT be affected by tanking as they are based on declared Max values from your Certifictae of Airworthiness?

fuel service - I don't understand this - 95% of your tanking will be from your base or bases, where you will have time to put the tanking fuel on before departure - can you explain more?

parking fees - turnround at destination will probably be limited by passengers on/off time BUT you will not be held up by refuelling and fire service cover if needed etc.

delays - again, I cannot see where these will come from? Can you explain?

I do believe that the 'fine-tuning' you are seeking will not be productive in real terms, and I do not think any of the other parameters will actually 'reverse' the economy of tanking.

hoover1
11th Mar 2009, 19:19
so you don't think you burn more fuel when you are heavier? 10% is not far off on the fuel you waste just carrying it. if you carry 2000 extra pound then you will burn 200 pound of that just carrying it. i do not think this is ridiculus.

Rainboe
11th Mar 2009, 22:32
I'm afraid your reply is too simple and ridiculous! What sector length are you talking about? Do you only fly one particular rotation? What about tanking 30 mins. Or 14 hours? Both cost 10% in fuel? Daft mate. Because that is what you have said!

haughtney1
11th Mar 2009, 22:52
Boeing 757/767 4% per hour to tank.

Falcon 900EX 5% per hour to tank.

As rainboe has said, without specific info, its difficult to extrapolate anymore.

Finzolas
11th Mar 2009, 23:39
Dear BOAC,

Fuel service, delay, parking fee... Previous replies mentioned some situations were those factors may have an impact, even if it is almost impossible to build up an equation with those parameters for all our network (17 AC, 450 different stations during the year).

Regarding heavier weights, I was not meaning it regarding fees.

We use a software to compute Take off and landing data. This allows us to optimise thrust reduction for take off with large savings regarding engine maintenance. (plus: datas are far more accurate and improved than the results from books...).

Tankering = heavier weight = more thrust required = less engine saving... even if this extra thrust is used to carry less expensive fuel, we should consider it in the global economy (I may look insane now... engineering studies perhaps).

Regarding landing, structural loads increase with heavier weights (even if below certified limits).

More over, my belief with tankering fuel practice is you fill more fuel than requires just to guarantee you will not need more... Finally, you carry fuel that you do not really need... B737, around 35kg per ton per flight hour from each extra ton carried !-( Large amount of fuel burn wasted for nothing... (I speak about the extra fuel from the extra fuel)


Well, after lot of thinking, I may make a single change to the current situation : I will present ECO fuel recommendation for 5 extra tons in stead of 1.

Why? For 737, when you evaluate carrying more fuel for cost reasons, you will try to take more than one single extra ton.

Therefore, the result for 5t will represent a more accurate data to be used than the one extrapolated from the first ton until reaching the desired amount. Hope it makes sense for you too.


Again, thanks for your contribution.

Best regards,

Fin

hoover1
12th Mar 2009, 04:10
a % does not depend on length of sector as it will be a % of the fuel burn not a number per hour a this would go up or down based on how much you weigh. thus we use %. 10% might be high but that is what we ue as a rule of thumb. for the 737-400. it is simple becuase it is a rule of thumb not percise but the pilots are the ones who make the decision on wether or not to tanker and a we all know us pilots are not to good at math. there is just too many numbers to remember. ;) it is just what we use not supposed to be a hard fact. if it is wrong then oh well at least it isn't my money we are wasting.

hoover1
12th Mar 2009, 04:21
here you go.

MATHEMATICS OF TANKERING
To determine the ' break-even cost difference' (Cbe), use the formula:

Cbe = ( (RFCh + CmT) / F(1-R) ) x ($/gal)

Where:
R is the percentage of the fuel carried which is consumed due to carrying its own weight. The percentage is expressed as a decimal. Here 10%, that is .1, is assumed.
F is the quantity of tankered fuel in gallons.
Ch is the price per gallon at home base.
Cm is the maintenance cost, including engines, per minute of flight.
T is the additional flight time incurred by the added fuel weight, in minutes.

Assuming 600 gal are tankered, the formula shows that the break-even figure is $0.069/gal. This means that the price of fuel would have to be about 7 cents per gallon more than at home base, just to break even. Obviously, the price difference would have to be much higher than the 7 cents per gallon to make it logical to tanker the 600 gal.

The savings per average trip can be expressed by the following formula: S = F(Cd - RCh - RCd) - CmT. Cd is the cost per gallon difference between home and destination.

Assuming a 600-gal tankering load, at 35 cents difference in price ($.52 at home base and $.87 at destination) and a $2.92/min maintenance cost, the savings comes to $151.96 per trip. The formula: S = 600[$.35 - (.1 x $.52) - (.1 x $.35) - $2.92/min x 2 min] = $151.96 per trip.

If many trips were made to this destination, an operator could reap considerable annual savings in fuel costs.

OverRun
12th Mar 2009, 09:15
hoover1

Many thanks for that formula - I'd been trying to find that one without success.

Just a thought, but is there anyone that can make an HTML page with this formula in (as a javascript I guess), and send it to me so I can stick it on the web for us to use (and to reference here and in the TechLog stickies).

Cheers
OverRun

bookworm
12th Mar 2009, 10:07
R is the percentage of the fuel carried which is consumed due to carrying its own weight. The percentage is expressed as a decimal. Here 10%, that is .1, is assumed.

Putting this together into a formula with some minor extra terms included doesn't change the fact that the key parameter is R, and R depends on the sector length!

BeViRAAM
15th Mar 2009, 11:06
The formula doesn't include the total flight time as a factor so it will not be able to differentiate between tanking over 30 mins or 14 hours. If you always fly sectors of roughly the same time you have no need to take account of this as it can be accommodated in the 10% figure, i assume in this case it has.

waren9
15th Mar 2009, 11:54
Have another read mate.

Sector length is factored. R as a percentage is infact dependant on sector length. Just like bookworm says.

mutt
15th Mar 2009, 12:46
So where do you find the % for the sector length? This formula shows an assumption of 10%, but i dont see any reference to sector length, so you cant use the formula.

Mutt

bookworm
15th Mar 2009, 13:18
Exactly. That's where it gets interesting. For an aircraft flying under approximately similar conditions over the same distance, the ratio of its take-off weight to landing weight is constant. So for any given sector you can use representative values of landing weight / take-off weight to work out what fraction of excess fuel you get to keep, or conversely fuel burn / take-off weight to work out how much fuel is burnt carrying it.

hoover1
15th Mar 2009, 21:18
this is from boeing so hopefully they can answer the question

http://www.iata.org/NR/ContentConnector/CS2000/Siteinterface/sites/whatwedo/file/Boeing_Fuel_Cons_Nov04.pdf

HugoRibeiro
11th Mar 2012, 15:51
Dear all!

I have a question about the formula of the CBE. How do I know if it is lucrative to tankering? if the formula result is negative?

Best Regards,

misd-agin
11th Mar 2012, 16:58
Posters mentioned 4% fuel burn per hour per pound of additional weight carried for a 737.

Used to be 3% for 757/767.

Using 777 and 737NG performance data appeared to indicate 2.5%. IMO 3% is close enough.

Maybe advancement in fuel efficiency has changed the percentage?

Green Guard
11th Mar 2012, 21:02
earn or loss in $ = Store tons x(Arr [$ / ton] / 1.04 ↑ hrs– Dep [$ / ton])

earn or loss in tons = Store / (1.04 ↑ hrs) –Store / (Arr$/Dep$)

Fuel Price $ / ton = 26.42 * (c/Gal) / SG(lb /Gal) if(kg / L ) / 8.3454

1.04 =1+ [4 % loss per hour]/100 , 3% etc. as per aircraft

TruthShouldMatter
12th Mar 2012, 00:11
Since airline fuel is contracted, what is the most disparity in fuel prices you have seen from your departure point?

Old Fella
13th Mar 2012, 12:31
My recollection for the B747 Classic is that it cost 6% of tankered fuel per hour and it was not uncommon to carry fuel for up to three sectors, e.g. Hong Kong-Taipei - Taipei-Seoul - Seoul-Taipei.

Vc10Tail
13th Mar 2012, 12:48
I recall reading that it's 4%/kg/hr for moder twin turbo fans and 6% for multi-engine turbo fans of the 80s..perhaps a little higher for the turbo jets/low by-pass ratio turbofans/duct fans of the 70s and earlier.

I imagine prevailing fuel price is incorporated in the algorithm.Current fuel prices are on the high side...which disfavours tankering.Low fuel prices favour tankering.

Also availability of fuel or lack-there-of might influence the decision to tanker...tanker cost not withstanding!

I stand to be corrected.

MetoPower
13th Mar 2012, 13:08
My believe is fuel tankering should be done only for operational reasons and not be driven by economic consideration.

One of those situation is positionning flights (no load).
Here you can uplift from the beginning the fuel for the 2 next flights (without having to call for fueller at the next station). You will in this case (if the fuel is cheaper at the first station) uplift much more than 1t.

The indicated information of gain or loss for 1 extra ton is then erroneous as you will extrapole from 1t to 5 or 6 or even more... but the gain is not linear...

Thanks for your contribution

Fin


Don't you contradict yourself on this one???

TruthShouldMatter
13th Mar 2012, 19:50
It's moot. You guys don't know what the company is paying at point A and B, any more then you know what the overhaul cost is that forces you guys to run it to the end with de-rated power.

That said, if you want to have a conversation about flight planning, efficiencies, costs, etc, then you need to be able to pick optimal altitudes, power settings, routes etc..if you cant, or are not able, then taking on a few thousand pounds of fuel here or there, saving $20 on the contracted price at destination A or B is really just academic and has little real consequence to the overall flight operation.

Denti
13th Mar 2012, 19:58
Oh well, yet another SSG.

Anyway, max cost difference i've seen so far was around 280$ per 1000kg of fuel. Can't comment on our longhaul operation, they might see larger differences.

framer
13th Mar 2012, 20:50
It's moot. You guys don't know what the company is paying at point A and B, any more then you know what the overhaul cost is that forces you guys to run it to the end with de-rated power.

7 points for using the word moot properly in a sentence. No points for knowing your sh1t. The OP is involved in his companies tankering policy making so he will definately know the fuel prices at A and B.

That said, if you want to have a conversation about flight planning, efficiencies, costs, etc, then you need to be able to pick optimal altitudes, power settings, routes etc..if you cant, or are not able, then taking on a few thousand pounds of fuel here or there, saving $20 on the contracted price at destination A or B is really just academic and has little real consequence to the overall flight operation.
Academic?
if you cant, or are not able, now thats academic!


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