Which Optimum level to use? CFP vs FMS?
In the mob I fly for, there are two schools of thought as to which cruise Flight Level should be chosen for cruise - the level provided by the CFP, or the optimum level calculated by the FMGS.
The former school reasons that the Computerized Flight Plan has been optimized for winds at all altitudes, while the "box" only knows the current wind.
The latter school says that the CFP has been created for forecast conditions and weights, which usually differ from the actual ones, and therefore the FMS Opt level is more valid.
I tend to lean towards the FMS supporters, but would like to learn others view on that.
Also, can anyone tell my why the A-320 FMGS won't calculate step-climbs? While we mostly operate quite short sectors (up to 3 hours), the FMS-computed optimum level in the beginning usually differs from the one at the end. Still, when I try to insert a step-climb, I get the message "no optimal". Why?