# Cost-Index Calculation

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Hello everybody!I apologise in advance about asking a potentially simple question, but I'm going to nevertheless! The question I have is about understanding the cost-index calculation.Am I right in thinking that:1) a high cost index (50-99) is Minimum time / Maximum Speed (hence the higher operating costs through higher fuel burn)2) a low cost index (0-50) is Minimum Fuel Burn / Maximum RangeIs this is true, then am I also right in thinking that these two formulas translate into:1) High Cost Index = Lower ROC, but therefore at a higher speed (ie. emphasis solely on being quick) - with the TOC being further away from your starting point. - And high ROD / steep descent2) Low cost index = steeper ROC, but at a lower speed (to gain altitude quicker over a shorter distance) - with ther TOC being closer to the original starting point- with a shallow ROD (to effectively glide-in an minimise fuel burn).I appreciate the above explanations are somewhat 3rd-grader like and that the cost index cacluation, in pairing off time costs with fuel costs, is far more complicated. But is my base level understanding of this correct?Any help much appreciated!Thanks and regards from EDDFEd

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A lower cost index results in a slower, steeper climb that gets you to cruise altitude sooner, increasing the time at optimum altitude. It provides a slower cruise mach and a shallower descent profile.A higher cost index results in a faster, more shallow climb, gets you to cruise altitude later, decreases your time at optimum cruise, provides a faster cruise mach (so you burn more fuel) and uses a steeper descent profile.Rob Elliott, EGPE InvernessPSS Airbus Support andAirbus Fleet Training Captain, British Airways Virtual airbus@speedbirdonline.co.ukhttp://www.speedbirdonline.co.uk/airbus.htmlhttp://www.bavirtual.co.uk

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