MRC speed vs Cost Index

[felixthecat]

Just trying to get something straight in my mind….

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

[ScepticalOptomist]

This may help:

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

[felixthecat]

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]

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]

Isn’t Cost Index Zero max endurance which is not necessarily max range?

Cheers,
BH.

[mustafagander]

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]

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]

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.

[mbcxharm]

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]

Thanks for the clarification :)

[felixthecat]

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]

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%.