Once upon a time aircraft were placed "on the step", a speed at which the Mach/IAS seemed to be stable and well known by old codgers and F/Es, some of whom were still around in BAs Classic 747s.
If I recall correctly, the CFP cost index Mach for them was .84, but the experienced aviators (not bean-counters) would demonstrate that .86 was a much more stable cruise Mach # and the resulting fuel consumption increase was negligible compared to CFP, with less thrust lever "hunting".
Has the FMC cost index obsession deleted this knowledge from our database as we drive around controlled by desk pilots?
