Cost index?

[Juud]

Vague idea what it could be. :confused:

Could someone firm that up for me?
Is there an easy way to explain it?


For example, how do the 2 numbers relate to eachother in "We'd normally fly at cost index 60, but on this flight it's cost index 300 because of cabin crew limitations". (cue slightly reproachful look over right shoulder in my direction) ;)

Is that linear relationship or like an algorithm or something else entirely?
And what is the price of a tonne of fuel please?

Confused of Oslo

[Mad (Flt) Scientist]

Airbus's "getting to Grips With Aircraft Performance" covers it in their terms. Get a download of it here (http://www.smartcockpit.com/pdf/flightops/aerodynamics/18) at SmartCockpit. Look in section 2.1.3. Economic Mach Number (MECON) for details.

The MECON value depends on the time and fuel cost ratio. This ratio is called cost index (CI), and is usually expressed in kg/min or 100lb/h

and

For instance, a cost index of 30 kg/min means that the cost of one flight minute is the same as the cost of 30 kg of fuel. This does not mean the fuel flow is 30 kg/min.

So "We'd normally fly at cost index 60, but on this flight it's cost index 300 because of cabin crew limitations" basically means:

"We'd normally fly at a speed where the cost per flight minute is equal to 60kg of fuel, but on this flight we'll fly at a speed where the cost per flight minute is equal to 300kg of fuel because of cabin crew limitations". In other words, they're flying faster, such that it's costing 5 times the rate they'd like per minute.

[ClimbSequence]

Cost Index equals to direct operational cost divided by fuel price.

CI= DOC/FP

The operational cost does not vary as much as the fuel price in diferent locations. So you'll probably end up with a diferent cost index depending the airport you are departing from. Each company provides a study of the routes and assign a Cost Index

Happy landings :ok:

[Juud]

Gentlemen,
With your answers + links and a good read-through of our Work & Rest Rules, not only do I now understand the question, I will also have a well-founded answer next time the chaps ask me. "Jude, why do we have to fly cost index 300 because of you guys in the cabin?"

Thank you. :ok:

[mutt]

Judd, just smile and tell them that they are getting home sooner :) The higher the CI number the faster the flight.

MFS, a cost index of 30 kg/min means that the cost of one flight minute is the same as the cost of 30 kg of fuel :confused::confused:I'm going away to think about this one.....

Mutt

[Mad (Flt) Scientist]

That's the text stright out of the Airbus doc I linked to.

I think what they're trying to do is calibrate the CI number. It's not, strictly, a dimensionless quantity. If CI is defined as [cost of time]/[cost of fuel] then if you express the first as $/[unit time] and the second as $/[unit fuel] then the dimensions of CI are [unit fuel]/[unit time] so if you measure fuel in kg and time in minutes, the CI should be kg/min, dimensionalised.

Now, what does a CI of 30 mean, in those units. Well, it means the $ cost of one minute of time is 30 times the $ cost of 1 kg of fuel. Obviously, if your dimensions used to calculate CI are different then a CI of 30 lbs/hr isn't the same as 30 kg/min. But the principle would be similar. I confess I'd never really thought of it as a dimensioned parameter, but I guess it makes sense that it is.

[mutt]

I confess I'd never really thought of it as a dimensioned parameterMe neither:D

But after trying the formula on some real life operating costs and fuel costs, it didnt work. :(

I guess that it should remain dimensionless.....

Mutt

[Red Impulse]

Have a rather fundamental question on the Cost Index. I'm having a difficult time understanding the Cost of Time component of the Cost Index. The problem basically lies on what to include and what to exclude from the Cost of Time.

Should a particular cost's time relatedness (whether it varies with increases in flying hours) be the excluding criteria or should it be the cost's nature, whether its related to operations or not, would be. Or it might also be both, that the costs to be included in the computation of Cost of Time should be operations and also time related.

For example, I have read that what should be included would only be those Direct costs (i.e. related to the operation of the aircraft), so anything done in the aircraft other than for its normal operation (e.g. cabin interior re-upholstery) should not be factored in. But what if, just for the sake of argument, the billable amount for re upholstery services were done with a fixed rate tied up to the aircraft's flying hours, would this cost be, in fact included in the Cost of Time computation ?

[Brian Abraham]

A short three page explanation you can print off and poke under the inquisitors nose Juud. ;)

http://www.boeing.com/commercial/aeromagazine/articles/qtr_2_07/AERO_Q207_article5.pdf

[j140870]

But what if, just for the sake of argument, the billable amount for re upholstery services were done with a fixed rate tied up to the aircraft's flying hours, would this cost be, in fact included in the Cost of Time computation

Any cost that is directly related to the aircraft operation and the amount of time flying is a plausible cost for inclusion. Non-linear costs such as delay should also be allowed for if impact to the operation exists (i.e. missed pax connections).