# Can't enter big cost index
**URL:** https://forum.navigraph.com/t/cant-enter-big-cost-index/16875
**Category:** Dispatch
**Created:** [September 8, 2024, 9:41am UTC](https://forum.navigraph.com/t/cant-enter-big-cost-index/16875 "2024-09-08T09:41:59Z")
**Posts on this page:** 9
**Page:** 1
### Author:  [@jacklin](https://forum.navigraph.com/u/jacklin)
#### Post date: [September 8, 2024, 9:41am UTC](https://forum.navigraph.com/t/cant-enter-big-cost-index/16875/1 "2024-09-08T09:41:59Z")
Hello, I’m flying with 321 and 777. In 777, I want to use CI 9999 and in 321 I want to use CI 999, but I can’t enter it in Simbrief. Can you solve this problem?
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### Author:  [@Vatnsfjord](https://forum.navigraph.com/u/Vatnsfjord)
#### Post date: [September 8, 2024, 12:09pm UTC](https://forum.navigraph.com/t/cant-enter-big-cost-index/16875/2 "2024-09-08T12:09:58Z")
Why are you using such a high cost index? Anything above 200ish won’t have any additional effect, definitely not when into the thousands
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### Author:  [@jacklin](https://forum.navigraph.com/u/jacklin)
#### Post date: [September 8, 2024, 12:26pm UTC](https://forum.navigraph.com/t/cant-enter-big-cost-index/16875/3 "2024-09-08T12:26:41Z")
actually, I’m flying toliss 321 and the flightfactor 777. There are difference between CI 100 and 400, and in ff777v2, 2000 and 3000 has significantly difference. That’s why I think I need the high CI.
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### Author:  [@dougsnow](https://forum.navigraph.com/u/dougsnow)
#### Post date: [September 9, 2024, 10:26am UTC](https://forum.navigraph.com/t/cant-enter-big-cost-index/16875/4 "2024-09-09T10:26:43Z")
In Boeing’s FMS manuals for the 777, they don’t publish data for CIs above 1000.
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### Author:  [@jacklin](https://forum.navigraph.com/u/jacklin)
#### Post date: [September 9, 2024, 10:54am UTC](https://forum.navigraph.com/t/cant-enter-big-cost-index/16875/5 "2024-09-09T10:54:37Z")
Actually, the reason I use cost index 9999 is that I have checked my FCOM, And it tells me from 0 to 9999 all of them is valid. I don’t have an English FCOM, but please see this translated from Chinese.
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### Author:  [@dougsnow](https://forum.navigraph.com/u/dougsnow)
#### Post date: [September 9, 2024, 12:00pm UTC](https://forum.navigraph.com/t/cant-enter-big-cost-index/16875/6 "2024-09-09T12:00:58Z")
At work, for our 777F, we plan a CI of 150; which is right around the LRC speed for the 777. I was working a flight, roughly 15 hours long, and the operations controller wanted to speed the airplane up to make up a little time, so I ran a plan at CI-1000.
To save 12 minutes; it would have cost over 10000 lbs of fuel; as the increase in fuel burn goes up with the square of the airspeed; as the parasite drag increases exponentially.
Needless to say, we didn’t do it that day.
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### Author:  [@jacklin](https://forum.navigraph.com/u/jacklin)
#### Post date: [September 9, 2024, 12:21pm UTC](https://forum.navigraph.com/t/cant-enter-big-cost-index/16875/7 "2024-09-09T12:21:07Z")
OK, Now I learnt that. but actually, I have an interesting question want to ask. This is not a simbrief problem but it actually impact on my flying very much. I was flying a long flight that day, And using CI 999, that’s a really big CI. But the plane flies slower and slower during the flight. At first that is about .85 but about 8 hours later the speed is only about .81. I thought that is strange. As you a real pilot, I want to ask that in econ mode with CI 999, is that normal like this speed decrease?
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### Author:  [@dougsnow](https://forum.navigraph.com/u/dougsnow)
#### Post date: [September 9, 2024, 12:39pm UTC](https://forum.navigraph.com/t/cant-enter-big-cost-index/16875/8 "2024-09-09T12:39:50Z")
It depends
On what weight units, lb or kg; Boeing’s manual, for cts/lbs, a CI-1000 should be around M0.84 at 350, based on gross weight.
That being said I do NOT trust any flight model for any Flight Sim unless they used manufacturer data for performance; and I doubt many have the Performance Engineer’s Manual…
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### Author:  [@jacklin](https://forum.navigraph.com/u/jacklin)
#### Post date: [September 9, 2024, 1:31pm UTC](https://forum.navigraph.com/t/cant-enter-big-cost-index/16875/9 "2024-09-09T13:31:24Z")
Yes, I don’t have that manual so that I can’t find the data of the performance. But I think a 777 only fly .81, that is almost slower than a 320.