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?

This may help:

https://www.boeing.com/commercial/ae...icle_05_3.html

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.

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

Cheers,
BH.

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.

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?

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.

Correct.

Boeing FCTM: “Entry of zero for cost index results in maximumrange cruise.”

Thanks for the clarification :)

You are correct LRC is MRC -1%. The trade between the increased speed and the reduced range is considered acceptable.

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%.