Hello, Stanislaw K, you wrote: SK> What for them to put in the schedule if it is possible to change height of flight and to ignore/use them? In order that on top you will not fly, and to fly below certain height means to burn too much fuel, and to passengers it will be not too comfortable in uneasy atmosphere. The matter is that the modern reactive engines are most economical at height. For example, for -320 lowering of cruiser height on a route on 2 km from the optimal causes reduction of a distance of flight at other equal on 12-14 %, and speed of flight decreases approximately on 20 km/h. It turns out that there is no special difference in time of flight and in fuel consumption to fly against a wind at optimal heights easier. If wind too strong, select bypass routes, but a word "bypass" hints that they not faster the shortest, under condition of absence of winds. By the way, tell, how it is possible to use a head wind for reduction of time of flight? Very interesting. SK> SK> Commercial use of the jet stream began on 18 November 1952, when Pan Am flew from Tokyo to Honolulu at an altitude of 7,600 meters (24,900 ft). It cut the trip time by over one-third, from 18 to 11.5 hours Now this nonstop flight occupies 7.5 hours half an hour from which is an advantageous influence of air flow. Reverse flight occupies 8.5 hours, if that. It is clear, why? And yes, it was the piston plane. Silly to it to refer, considering the modern aircraft.