Flying under Instrument Flight Rules, pilots cannot fly wherever they want. They have to fly only on specified routes. The aircraft must have many special devices working with radio waves such as GPS or radar. The air routes lead mostly from radio beacon to beacon. Pilot must set the correct frequency of the beacon to determine the bearing and fly to it. GPS helps to find exact position. Each aircraft also has a radar transponder sending a special code that is indicated on air traffic controller’s radar screen. Because pilot does not see outside, he has to do what the controller says. The controller makes sure that the aircraft does not crash. 