Just a hint, Alexander: The cargo bird isn't flown any different than the pax bird, and the flight plan isn't any different either.
Your obsession with the "cost-index" is unnecessary. It's only a guide. I can set 80, or I can set 120, or whatever... The reality is that on most routes Mach Number is maintained; so if the FMS calls for "optimum" altitude to be FL334 and M.856, it's inconsequential...because you can't fly at FL334, and maybe you're stuck at FL 280 for 2 hours before you can climb up to FL330...it's real world stuff. Maybe ATC wants you to maintain fixed Mach for spacing...so you can't follow the FMS "optimum" parameters. When you cross the pond you're also flying fixed Mach, probably M.86...not what the FMS says!
And when you get to the end of the rainbow with the approbriate STAR programmed into your FMS, then ATC always has different plans for you, especially at busy airports with traffic saturation...Can't descent when FMS calls for "optimum" descent point, or must descent early...screws up your "optimum" profile. Maybe ATC has you down to 11,000 feet 50 miles out going into Newark and has you vectored all over the place at low altitude, maybe even has you slowed down where you have to select flaps earlier than planned....now all your FMS "cost index" is already blown to bits...and when you go into Heathrow at peak arrival times...bingo...you're into a holding pattern...that's why the setting of a "cost index" is altogether overrated in the real world. As a prospective dispatcher you would be well to do to sit in the cockpit and get a dose of the real world to balance your theoretical studies of flight planning.
