From HF Underground
Major World Air Route Area (MWARA) Frequencies
Vast areas of the world lack the necessary VHF communication systems needed to provide reliable radio coverage between aircrews and air traffic controllers. This lack of VHF coverage is generally due to their remote locations - for example much of the airspace over the Atlantic and Pacific oceans. To compensate for this lack of VHF coverage a group of HF Frequencies has been allocated as detailed by the following maps.