I mean, let's imagine the CI of a B737 is around 25. If you wouldn't touch the speeds (climb/cruise/descend) in the FMS after entering the CI, the computer calculates the speeds based on the CI (right?). But if you enter the CI, and then enter something like mach 0.74 in the cruising page, the CI doesn't matter, because you manually changed the speeds... Is that all correct?So why do you have to enter an Cost-Index in the FMS when dispatch gives you the speeds anyway?It is my understanding that it is not just the speeds that the CI value would affect.
For example, a low cost index will not only result in lower climb, cruise and descent speeds but also a generally higher cruise altitude and a later descent.
One possible reason for your example having assigned speeds is that because with a varying CI, even aircraft in the same fleet of the same airline will perform differently.
