Cost index.

[Captain Vortex]

Does anyone know how to calculate cost index for a B737-300? Or even for any a/c?

[The Edge]

At the risk of starting a major discussion, Cost Index is defined by Boing as

Time Related Costs(in $ per flight hour)
Divided by Fuel Cost (in $ cents per pound).


Yes, I know thats not very helpful, but thats the definition !!

[mcrit]

Of course its Airline specific. It depends on the company priorities with regard to flight time vs. fuel cost. Cheep charter would probably have a lower cost index than say a VIP jet of the same type for example. Hope this helps.

[mach 84]

our company has started to use costindex too.
however cannot follow the idea behind. if i
use a fixed mach number instead of econ crz,
i might burn off a ton of fuel more, but will be 15 mins faster there. is 15 mins of aircrafttime cheaper than a ton of fuel??


[This message has been edited by mach 84 (edited 12 March 2001).]

[geh065]

It could be, if it means your pax have tight flight connections, or if a short turn-around time is planned, especially if you are late already.

[Speedbrake UP]

That is the great thing about an FMC. I put in a cost index then check the progress page. Compare the arrival time versus fuel at destination and make a decision. Do I like what I see - leave it - don't like what I see - change it back.

Usually find in a 767 that a cost index of 60-80 gives a good medium between flight time and fuel usage. A cost index of 250 can be a pain, watching the speed with one hand on the thrust all night. Makes a long night!

69 was always a good number http://www.pprune.org/ubb/NonCGI/cool.gif

[Compliant One]

The one of the reasons for Cost Index is that you can alter the arrival time in the most efficient manner. By altering the cost index rather than manually selecting the cruise speed, a continuously adjusting target is obtained. The descent speed is also calculated for the CI.

Strictly speaking, the CI was invented by some very clever people in the industry to address a problem that was done by guesswork before. What target speed should we fly at for minimum cost taking both Fuel and Rotable /maintainance costs into account.

Almost all airlines now simply pick a standard CI for the a/c type. I guess that it is simply too expensive to monitor all the costs at different ports and maintainance providers.

Use CI to obtain the best result to a "how do I save (or loose) time".

Compo

[Jambo Buana]

The three variables of cost index are:
1). Crew costs per hour
2). Maintenance costs per hour
3). Fuel costs

If you fly LRC your speed will reduce as your weight reduces. But you will get more MPG than any cost index value.

In the Gulf they used to fly around at max mach cos fuel was zip. ( high CI )

In Europe most 737 operators who don't care too much about time constraints fly between 30 - 40.

Just be careful though if you are behind THY who fly slowly cos they are paid by the minute. 160 kts at 20 nms is the norm!!

[O\ZON]

your not supposed to change the CI when inflight.
if f***s up its principle.
It can be changed on ground to save time, but airbus recommend that you do not change it inflight.

o/Z

[Zeke]

The cost index (CI) is a ratio of the cost of flying time, to the cost of fuel.

To calculate the CI, divide the operating expense of the aircraft, excluding fuel, by the cost of fuel in cents per pound/kg.

The cost index for an aircraft that is configured in pounds for ZFW/fuel etc will be different for a metric aircraft to give the same performance.

Low CI = slower speed
High CI = higher speed

Operators can bump up the CI for items not directly "seen" as being direct operating expenses, i.e. the cost of curfew charges, hotel accommodation for all the passengers if the aircraft cannot get out before a curfew on a later flight, flights going into a known predictable headwind/jet stream etc. A company may offset the cost of burning a little more fuel than the cost and inconvenience of delaying passengers.

They can be stored in the flight management computer with the company route and automatically inserted when the company route is selected.

The CI is only one of many factors the flight management computers use, other factors it uses includes, ZFW, ZFWCG, speed constraints/limits, ECON speeds, Temps/Altitudes of the tropopause, performance data for the airframe and engine, cruise flight level, current CG, current and forecast winds climb/enroute/descent/destination, OAT and more....

Cheers

Z

O\ZON

Do you have the Airbus/Honeywell reference to the recommendation of Airbus not to change the CI in flight ?

[O\ZON]

Zeke.
am afraid i cant name page and reference off hand.
However Airbus produced a good booklet on cost index (about 40 pages) on its use and calculation.
Its called "Getting to grips with Cost Index" or something along them lines.
i think personally its gives more indepth analysis of change and effect than the corresponding boeing one does.

rgds
O\Z

p.s. it would be great if we could get a spell check for posts.
Besides that - an excellent site