Thank Grasscarp,
Surely it's all automated with taking into account winds, weight, etc, but when selecting direction of Flight Levels on particular airway - odd or even, do you rely on table of cruise flight levels or refer to ATS routes section of AIP?
Simple example. Airway X, from navaid A to C. Magnetic track 140. RVSM. According to "table of cruise flight levels", FL should be odd. However AIP prescribes even FL's on airway X from navaid A to C. Would you file for odd or even FL and why?