<P> For much of the 20th century, 500 kHz was the primary international distress frequency . Its use has been phased out in favor of the Global Maritime Distress Safety System . </P> <P> Use of some distress frequencies is permitted for calling other stations to establish contact, whereupon the stations move to another frequency . Such channels are known as distress, safety and calling frequencies . </P> <P> Satellite processing from all 121.5 or 243 MHz locators has been discontinued . Since February 1, 2009, the U.S. Coast Guard only monitors distress signals from emergency position indicating radio beacons that broadcast using digital 406 MHz signals . Digital 406 MHz models became the only ones approved for use in both commercial and recreational watercraft worldwide on January 1, 2007 . </P> <P> International distress frequencies, currently in use are: </P>

What is the coast guard emergency hf frequency