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Cost Index

Old 22nd Aug 2000, 09:12
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jtr
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Question Cost Index

Does anyone have any gems relating to CI, (on the Bus). I have seen/heard a few different ideas, but nothing concrete. Basically trying to find out what, if anything that the number relates to. Something a little deeper than the 'best time/best fuel' explanation that the FCOM's offer.
Cheers, Jack
 
Old 22nd Aug 2000, 20:27
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Smebruce
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Cost index is derived from the following formula, ocph/(fp*100)
opch= operating cost per hour, (US$ per hour)
fp= fuel price, (US$ per kg)
The operating costs per hour has a multitude of factors which ifluence it, turn around times, airframe life, crew costs, delayed flight, and MAINTENANCE COSTS. Think of a operting cost and add it to the
variable "operating costs".
Maintenance costs are the least known about of all the variables by the Bean counters.
However, the price of fuel is the biggest influence in determining the cost index
 
Old 22nd Aug 2000, 22:35
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jtr
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Thanks for the reply Smebruce, but now I`m elevated to a higher level of confusion.
If I fly from A to B at CI 60, x kg of fuel will be burnt. If I fly the same route at CI 150 x+ kg of fuel is burnt. With regards to the second instance, the overall result is an increase in opch due extra burn (outweighs higher utilization of a/c time vs. sectors). Thus when comparing the two scenario`s the increase in fuel burn should be a large one (for your formula to work), whilst in reality, it is not. I am not doubting your explanation, I am just wondering if there is more to the formula?
 
Old 23rd Aug 2000, 00:05
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mutt
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Try flying an aircraft that burns more fuel than an A320! Then the numbers really do start to make sense.

Also do a search over the last 20 days, you will find another discussion on Cost Index for the B744. The principle is the same.

Cya

Mutt
 
Old 23rd Aug 2000, 00:58
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jtr
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I`m talking about the A330 and 340, which do burn more. The main hole in the opch/fuel cost is that CI = 0 exists, mathematically this can only be so as opch approaches 0 or fuel cost approaches infinity...

[This message has been edited by jtr (edited 23 August 2000).]
 
Old 23rd Aug 2000, 17:12
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Smebruce
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Hmmm, methinks that operating cost/h and TOTAL COST for a sector are confused, try the following equation for total cost. Tc=(fp*tff)+(opch*tft)
fp= fuel price
tff= total flight fuel
opch= operating cost per hour
tft= total flight time
Hope it helps you out

Bye.
 
Old 23rd Aug 2000, 18:05
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Smebruce
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PS. I forgot to add, jtr you are quite right with your interpretation of the CI=0. If the opch is zero then you can keep the airplane in the sky all day, for the crews, maint etc.... are not costing you a penny (not realistic) irrespective of how expensive the gas is. Or if you have normal operating costs but VERY, VERY expensive fuel then you want the cost index close to zero as well to minimise the fuel burn for the sector. being up forever is no fun.

Bye.
 
Old 23rd Aug 2000, 18:27
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jtr
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hmmm.. Thanks for your replies. I am still a little (actually a lot) confused, but I can see where you are coming from. I have heard about 5 different ideas on the line, and just wanted to confirm which, if any, were correct. Had heard something similar to your explanation, but couldn't stick it with all scenarios.
Yes, I was one of those kids that made the teachers eyes roll when my hand went up. Thanks again
 
Old 23rd Aug 2000, 20:18
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Smebruce
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Confucious say,
When confused and nothing makes sense
think like a Bean counter and everything makes cents

Bye
 
Old 24th Aug 2000, 01:26
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mutt
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One of the MAIN problems with CI is that its fictitious. Nobody can make it work properly.

Mutt
 
Old 25th Aug 2000, 03:00
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Boxer
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jtr....
to add to your confusion, all of the above are correct.... your queirie re CI0... well as you know if it flys, floats or F**** then you have to pay for it. CI 0 does not in practise give you best fuel econ due body angle just as 999 does not increase A/C performance. CI is only effective if each A/C has a flight plan which is relevent to each particular one (history fuel burns) and the perf factor on A/C status page is updated to the corrected index. Now we must add in our variables (fixed variable and so on..). I have flown for different operators who use different CI's. Bottom line.... very few companys use same correctly as it is too much effort correcting the CI for all flights due to route costs, winds aloft, temps aloft, schedule and so on....
Happy hunting............

[This message has been edited by Boxer (edited 24 August 2000).]
 
Old 26th Aug 2000, 10:32
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tailwinds
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jtr,
just quoting/unquoting, call it sharing information.
"""CI gives the Mach number that minimizes direct costs per flight hour.
Direct cost = Fc .c + Pt.t + Fc
Fc : fuel cost (/Kg)
c : fuel consumption (Kg)
Pt: maintenance + crew costs /flight hour
t : flight time
Fc: fixed costs ( maintenance costs/cycles, handling, fixed salaries, pax fixed costs, depreciation)
If we want to minimize this direct cost, we have to minimize Fc.c + Pt.t... After a small mathematic development, we find that the Mach number that minimizes the direct costs per flight hour depends on the following ratio:
CI = Pt/Fc (CI: cost index)
This shows that it doesn't make any sense to fly a CI if it is not specifically computed for each leg.... CI is really related to price of fuel and the amount of fuel that you take at a certain price ( economical tankage & through tankage considerations).
If your company doesn't perform this calculation for each leg, it makes more sense to fly a fixed Mach number. CI only affects ECON speeds. If you played a little bit with your FMS, you realized that if you change the CI, OPT FL will change (but not MAX FL, of course): the higher the CI is, the lower the OPT FL is. Also tail/head wind has an important effect. These 2 examples prove that price of fuel has to be considered if you use the CI.""""
apologies to the 'chappy' who wrote this.
and thank you!
 
Old 29th Aug 2000, 14:58
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Smebruce
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Just a note here, I am not familiar with either the FMS/FMC, but with the PMS the cost index can only be changed and inserted on the ground,

Bye.
 
Old 2nd Sep 2000, 04:52
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Fast Erect
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Sorry to sound simplistic on this matter, but my answer to this typifies most things Airbus...!
It just does!

Don't worry your little head over such trivialities.
Extract the CI from your company issued graph and type it into the MCDU.....bish,bosh...go flying!

Hope this goes absolutely nowhere near answering your question!!

Fly safe,
FE
 
Old 2nd Sep 2000, 17:41
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jtr
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Fast Erect, are saying that you are allowed to change your CI in the MCDU? Hell I go dizzy at the thought of that much finger power. I just fly it with whatevers in there
 

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