I have read various suggestions on the Cost Index to use. One as low as 90 and another as high as 800. I believe the lower the number, the less fuel is consumed. However, I tried 90 with an aircraft carrying a 206,000 lbs of fuel and a ZFW of 509,000 lbs and found that for the first few hours the climb rate was about 200 FPM.What in your opinion, on a long flight, is a nice balance between performance and fuel consumption? Would 500 be too high?ThanksStanner

G'Day Stanner. We use cost index 100 for the majority of our long flights. Ocassionally you get a C.I 500 plan but that would only be for a quick flight like YSSY-YMML or YSSY-NZAA for example.The most fuel efficient C.I is around about 300-350. Individual operators use differnet C.I profiles depending on what they have decided is best for them. They base it on maintenance costs, engine wear, fuel burn over the sector, time for the sector etc etc etc.For example as I said we use C.I 100, but at Sing Air they just use a constant Mach cruise of M0.86So the best thing to do is get airborne and established in the cruise. Open the speed window, and start changing the C.I up and down and looking at the ETA and fuel over destination on the Progress page, write them down and you will see a trend for the different C.Is. You can even plot it out as a graph, it makes for an interesting exercise. Regards Steve PowerS/O 744Sydney

Steve,And a good day to you. Thank you for the reply. I did not know that the Cost Index could be changed while in flight. Thank you.Stanner