FMC setup question - 757

[RHaas]

Hey guys, I bought my first payware Airliner a few weeks ago and have been forced to learn FMC enough so I can fly my new qualitywings 757.

In the FMC setup section where you input the Cost index and Reserves I noticed that most of the tutorials I watched are using 80 for the cost index and 20 for reserves but no explanation was ever given as to why those values were chosen.

 

So my questions is, what is this used for, what is it doing and how and why would you decide what will be the best numbers to input in that section?

 

Thanks

[Matthew Kane]

From Boeing:

 

Cost Index setting varies according to company policy or current market price for fuel etc explained here:

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

 

Reserves is your fuel reserves so you do not run out of fuel. Too low a setting and with heavy head winds you may run very low or run out. I higher setting you will need to load more fuel. 

 

A few Google searches and a lot of info. Also the Captain Sim manuals have explanations as well.

[rick66]

1 hour ago, RHaas said:

20 for reserves

I have my doubts a figure of 20 hrs reserve would be used, its missing the decimal point, it should read 2.0.

Cost Index is simple.

High CI=More fuel burn+Lower flight time+Lower Crew times=Less $$ for the Airline

Low CI=Less fuel burn+Higher flight time+Higher Crew times=More $$ for the Airline

[RHaas]

6 minutes ago, rick66 said:

I have my doubts a figure of 20 hrs reserve would be used, its missing the decimal point, it should read 2.0.

Cost Index is simple.

High CI=More fuel burn+Lower flight time+Lower Crew times=Less $$ for the Airline

Low CI=Less fuel burn+Higher flight time+Higher Crew times=More $$ for the Airline

 

Hi Rick... I'm pretty new to FMC and would not surprise me if I was doing it wrong. what would the range be for High and low CI?  1 to 100?

 

As an example, Lets say I was doing a 5 or 6 hour flight at a cruising alt of 33,000. What would be a typical CI value

[rick66]

1 hour ago, RHaas said:

Lets say I was doing a 5 or 6 hour flight at a cruising alt of 33,000. What would be a typical CI value

So it depends on other external factors also, Your forecast winds aloft will have a major influence on the correct CI you choose, if you have high cross winds or head wind components at cruise you will want a medium CI, but your safe to pick CI between 60-78, you also have the ability to tone it down again with the LRC (long range cruise) settings inside the FMC, this will further reduce N1 power in the cruise.