Airspace is now one of the most frequently mentioned environments when discussing technologies of autonomous or unmanned vehicles or machines. There is a number of technologies developed to support unmanned flying vehicles (UFV) and so called air drones. The actual influence of such kind of machines on transport industry is crucial. It is also obvious, that many modern military operations involve UFV with built-in AI or remote control. Nevertheless, one of important problems for any flying vehicle (aircraft or drone either) is to plan the most suitable route satisfying all necessary primary and collateral requirements: reach destination, consume minimum fuel or energy, follow the safest areas, avoid adverse circumstances etc. Among the tasks to build the effective route for the flight we find an important problem to cut a relevant area in airspace to perform route search. This research is dedicated to discuss and ground the basics of a reliable approach to solve this problem.