I`m just wondering if there is a rule of thumb for choosing your Flight level when creating a flight plan ??For example , 1000 feet msl for every 150nm ??Thanks

I'll try to answer as best I can. Please recognize that I am not an expert so this will be a simplistic explanation.Every aircraft type (eg. A330/B747/B767/B777) will have an optimum flight level based on current aircraft gross weight. The optimum altitude will increase as the aircraft burns off fuel. Fuel burn penalties will be incurred for flying below, or above, the optimum flight level.The most fuel efficient operation of the aircraft would be to fly at the optimum altitude the entire flight. This is not practical as it would mean the aircraft would be in a long slow climb the entire flight.Step climbs are used by airlines to combat this. The aircraft will first climb to, and fly at, an altitude slightly above optimum. As it burns fuel it will cross optimum, and finally will be below optimum. Then it will climb to it's next flight level and repeat the process until it reaches it's destination.Step climbs are typicaly performed in two thousand or four thousand foot increments.In very rough numbers, the step climbs would occur every two to three hours during flight.Hope this is what you're looking for and that I explained it properly.Bob.

thanks for the info..It helps.