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Mandatory Frequency (MF)
From SKYbrary Wiki
In some parts of the world, the regulating authority may designate a Mandatory Frequency (MF) for use at selected uncontrolled aerodromes or at aerodromes that are uncontrolled during specific hours. An MF area will be established at an aerodrome if the traffic volume and mix of aircraft traffic at that aerodrome is such that there would be a safety benefit derived from implementing MF procedures. When a MF has been established, the specific frequency as well as the distance and altitude within which MF procedures apply will be published. Aircraft operating within the area in which the MF is applicable (MF area), on the ground or in the air, must be equipped with a functioning radio capable of maintaining two-way communication unless a Flight Service Station (FSS), Community Aerodrome Radio Station (CARS) or other similar agency is in operation and specific prior arrangements have been made.
There may or may not be a ground station in operation at the aerodrome for which the MF area has been established. When a ground station, such as a FSS or a CARS, is in operation, all aircraft reports that are required for operating within, and prior to entering an MF area, shall be directed to the ground station. However, if there is no ground station or if the ground station is not in operation, all aircraft reports required for operating within and prior to entering an MF area shall be broadcast "in the blind". Refer to the article Uncontrolled Aerodromes - Communications for specific reporting requirements.