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MRC speed vs Cost Index

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MRC speed vs Cost Index

Old 16th May 2023, 22:35
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MRC speed vs Cost Index

Just trying to get something straight in my mind….

Assuming still air will MRC give the same speed as Cost index 0?
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Old 16th May 2023, 23:51
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This may help:

https://www.boeing.com/commercial/ae...icle_05_3.html
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Old 17th May 2023, 03:21
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Originally Posted by ScepticalOptomist
Thank you for the link, unfortunately that was partialy where my question had come from originally when I had read it.
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Old 17th May 2023, 05:39
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Originally Posted by felixthecat
Thank you for the link, unfortunately that was partialy where my question had come from originally when I had read it.
Oops. 🤣

My understanding is that you are correct.
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Old 17th May 2023, 10:37
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Isn’t Cost Index Zero max endurance which is not necessarily max range?

Cheers,
BH.
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Old 17th May 2023, 11:44
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Cost Index, CI, allows for all costs while MRC is solely about maximising the range achieved with the fuel available. Hence they are unlikely to be the same speed.
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Old 17th May 2023, 19:32
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CI = time costs per hr/fuel cost per lb. With CI 0 it is that other incidental costs are irrelivent, only fuel cost is relivent. Hence my question, in effect is CI 0 giving MRC in still air?
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Old 18th May 2023, 03:45
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Originally Posted by Bullethead
Isn’t Cost Index Zero max endurance which is not necessarily max range?

Cheers,
BH.
CI 0 = max range. Green Dot speed = Max endurance.
LRC if I remember correctly you lose like 1% of max range compare to CI 0 but gain like 3% on the speed.
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Old 18th May 2023, 05:32
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Originally Posted by felixthecat
CI = time costs per hr/fuel cost per lb. With CI 0 it is that other incidental costs are irrelivent, only fuel cost is relivent. Hence my question, in effect is CI 0 giving MRC in still air?
Correct.

Boeing FCTM: “Entry of zero for cost index results in maximumrange cruise.”
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Old 18th May 2023, 15:22
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Thanks for the clarification
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Old 18th May 2023, 15:24
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Originally Posted by pineteam
CI 0 = max range. Green Dot speed = Max endurance.
LRC if I remember correctly you lose like 1% of max range compare to CI 0 but gain like 3% on the speed.
You are correct LRC is MRC -1%. The trade between the increased speed and the reduced range is considered acceptable.
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Old 29th May 2023, 22:25
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LRC was created by Boeing back before FMC's, ECON speeds & cost index computer data analysis. It provided an average compromise between fuel consumption & hourly operating cost that was very good for it's time. Speed wise I think it was Mmr Mach plus 5%.

Last edited by Private jet; 30th May 2023 at 07:13.
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