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felixthecat
16th May 2023, 22:35
Just trying to get something straight in my mindÖ.

Assuming still air will MRC give the same speed as Cost index 0?

ScepticalOptomist
16th May 2023, 23:51
This may help:

https://www.boeing.com/commercial/aeromagazine/articles/qtr_4_07/article_05_3.html

felixthecat
17th May 2023, 03:21
This may help:

https://www.boeing.com/commercial/aeromagazine/articles/qtr_4_07/article_05_3.html

Thank you for the link, unfortunately that was partialy where my question had come from originally when I had read it.

ScepticalOptomist
17th May 2023, 05:39
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.

Bullethead
17th May 2023, 10:37
Isn’t Cost Index Zero max endurance which is not necessarily max range?

Cheers,
BH.

mustafagander
17th May 2023, 11:44
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.

felixthecat
17th May 2023, 19:32
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?

pineteam
18th May 2023, 03:45
Isnít 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.

mbcxharm
18th May 2023, 05:32
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 maximum range cruise.”

felixthecat
18th May 2023, 15:22
Thanks for the clarification :)

felixthecat
18th May 2023, 15:24
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.

Private jet
29th May 2023, 22:25
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%.