Cost index
Airbus 320
the cost index is a strategic parameter in cruise.it is to be changed only for strategic purposes such xtra fuel getting close to 0 or flight time considerations ( in this case i prefer select a given fixed cruise mach number on FCU and all predictions will be update accordingly)
Be in mind tha any time we changed the cost index the FMS will be computed for a optimum flight level, optimun step level
i never won more time in speed up the mach in cruise but if you decide for a high speed approch and quick rotation on ground you can get some more minutes or be on time .
Nice high speed app