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Distress signal

From Academic Kids

A distress signal is an internationally recognized means of obtaining help by using a radio, displaying a visual object or making noise from a distance.

The most well known distress signal is the Morse code group SOS, which is sent as di' di' dit dah dah dah di' di' dit, ...---.... This is sent with no spacing between the S and the Os, bar-SOS in telegraphic notation.

Another distress signal is the code word Mayday. The keyword MAYDAY should only be used from a vessel or aircraft in immediate danger of sinking or crashing. The keyword PAN-PAN may be used when the call is very urgent. Certain radio frequencies are preferred for emergency calls. Ships use VHF channel 16 (156.8 MHz) and 2182 kHz. Civilian aircraft use 121.5 MHz. Military aircraft use 243 MHz. Aircraft can also signal an emergency by setting one of several special transponder codes, such as 7700.

Mayday and SOS are to be sent in groups of three. Distress can be signaled by any unusual action repeated in groups of three. This could be three puffs of smoke (by covering and uncovering a campfire), three gunshots, three blasts of a whistle or horn, and so on.

Other distress signals are primarily for use in rural or isolated areas, or in the wilderness. Survival training includes ground to air signals that can be used to signal passing aircraft with flares, mirrors or marks made on the ground or snow (e.g. the letters "SOS"). These signals should not be used except in an actual emergency and should be destroyed when the person signaling is rescued. Pilots will sometimes take extreme risks to locate and report what they believe to be an emergency signal from the ground.

Emergency beacons aboard aircraft and surface ships may be activated upon a crash or contact with water (as in a sinking). Modern beacons transmit a radio frequency signal at 406 MHz, while older beacons transmit signals at 121.5 MHz or 243 MHz for civil and military purposes, respectively. These beacons can be detected by satellites, which relay the signal to nearby rescue services. The use of satellites makes it possible for signals sent from remote locations to be picked up.

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