Originally Posted by
Ledhead27
As an additional question, would the application of using the ECON mode within the aircraft's FMC have any further effect time and/or fuel saving? I understand that ECON mode is related to Cost Index & is acquired by an algorithm, but but how would one describe the factors that influence ECON mode?
Normal line flights in fairly modern aircraft are conducted always with cost index as the primary performance factor. It's a matter of balancing the time costs (flight hours being put on the aircraft and its components, crew time=$$$) and fuel costs, for a particular pair of airports.
The higher the CI, the higher the speed, the lesser the flight time= more fuel being burnt. CI 0 is long range cruise, CI 99 or 999 (depends on FMS software) is max cruise speed.
N1EPR: On those flights with lower cruise altitudes the aircraft doesn't reach our usual "changeover" Mach number, which is about 0.76 with our regular cost index. So we actually fly a higher IAS than at 360(obviously), but Mach is usually around 0.61-0.67 or thereabouts. TAS is lower too, around 400