For Airbus:-
Cost index 0 = achieve minimum fuel.
Cost index 999 = achieve minimum time.
So basically, by entering a cost index, you're telling the FGMC/FMGEC how to adjust the flight profile, (when to climb, when to descend, what speed and flight level to fly at), to achieve the cost savings, or time savings that you need.
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Last edited by Uplinker; 19th Jun 2012 at 02:47.