In aviation, a flight information region (FIR) is a specified region of airspace in which a flight information service and an alerting service (ALRS) are provided. It is the largest regular division of airspace in use in the world today. FIRs have existed since 1947 at least.
Every portion of the atmosphere belongs to a specific FIR. Smaller countries' airspace is encompassed by a single FIR; larger countries' airspace is subdivided into a number of regional FIRs.
Some FIRs encompass the territorial airspace of several countries. Oceanic airspace is divided into Oceanic Information Regions and delegated to a controlling authority bordering that region. The division among authorities is done by international agreement through the International Civil Aviation Organization (ICAO).
There is no standard size for FIRs – it is a matter for administrative convenience of the country concerned. In some cases there is a vertical division of the FIR, in which case the lower portion remains named as such, whereas the airspace above is named Upper Information Region (UIR).
An information service and alerting service are the basic levels of air traffic service, providing information pertinent to the safe and efficient conduct of flights and alerting the relevant authorities should an aircraft be in distress. These are available to all aircraft through a FIR. Higher levels of Air Traffic Advisory and Control services may be available within certain portions of airspace within a FIR, according to the ICAO class of that portion of airspace (with regard to national regulations), and the existence of a suitably equipped authority to provide the services.