instrument flight rules
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instrument flight rules[′in·strə·mənt ¦flīt ‚rülz]
Regulations governing flying when weather conditions are below the minimum for visual flight rules. Abbreviated IFR.
instrument flight rules (IFR)
Rules and regulations established by the ICAO (International Civil Aviation Organization) and the national regulatory authorities to govern the flight rule conditions in which the flight by outside visual reference is not safe. IFR governs the flight of aircraft along controlled airways and airports, and aircraft separation is controlled by the operators from the ground. Flight according to instrument flight rules is done by reference to instruments in the cockpit; the aircraft is navigated by reference to electronic signals. For flying under IFR, aircraft shall be equipped with suitable instruments and with navigation equipment appropriate to the route to be flown. An IFR flight shall not normally be operated over high terrain or in mountainous areas at a level less than 2000 ft (600 m) above the highest obstacle located within 5 miles (8 km) of the estimated position of the aircraft. In areas other than these, the minimum flight level shall be at least 1000 ft (300 m) above the highest obstacle within 5 miles (8 km) of the estimated position of the aircraft.