Any aircraft in Classes ‘F’ and ‘G’ airspace may use the country-wide Flight Information Service which is available on one of several frequencies. Aircraft are not obliged to contact the Flight Information Service but the service is available for advice and information. It is not the same as being under control. Flights generally route from one aerodrome area to the next, taking advantage of the Flight Information Service in the uncontrolled airspace between aerodrome radar areas. The FIS offers information concerning weather, conflicting traffic, airport conditions, liaison between aerodrome control areas and clearances to join or cross airways. Since airways and TMAs have a lower level, aircraft may pass beneath them and remain in uncontrolled airspace. Aircraft in uncontrolled airspace have to comply with certain rules. Basically they must fly on a ‘see and be seen’ rule, or if weather conditions are unsuitable, on an instrument flying rule. They are known respectively as Visual Flight Rules and Instrument Flight Rules, abbreviated to VFR and IFR.
There is special Advisory Area and Advisory Route. Advisory Area is a designated area where air traffic advisory service is available. Advisory Route is a designated route along which air traffic advisory service is available.