Call for help

A distress signal or distress call is an internationally recognized means for obtaining help. Distress signals are communicated by transmitting radio signals, displaying a visually observable item or illumination, or making a sound audible from a distance.

A distress signal indicates that a person or group of people, ship, aircraft, or other vehicle is threatened by serious and/or imminent danger and requires immediate assistance. Use of distress signals in other circumstances may be against local or international law. An urgency signal is available to request assistance in less critical situations.

In order for distress signalling to be the most effective, two parameters must be communicated:

For example, a single aerial flare alerts observers to the existence of a vessel in distress somewhere in the general direction of the flare sighting on the horizon but extinguishes within one minute or less. A hand-held flare burns for three minutes and can be used to localize or pinpoint more precisely the exact location or position of the party in trouble. An EPIRB both notifies or alerts authorities and at the same time provides position indication information.

Distress signals at sea are defined in the International Regulations for Preventing Collisions at Sea and in the International Code of Signals. Mayday signals must only be used where there is grave and imminent danger to life. Otherwise, urgent signals such as pan-pan can be sent. Most jurisdictions have large penalties for false, unwarranted or prank distress signals.

Distress can be indicated by any of the following officially sanctioned methods:

A floating man-overboard pole or dan buoy can be used to indicate that a person is in distress in the water and is ordinarily equipped with a yellow and red flag (international code of signals flag "O") and a flashing lamp or strobe light.

In North America, marine search and rescue agencies in Canada and the United States also recognize certain other distress signals:

In addition, a distress can be signaled using automated radio signals such as a Search and Rescue Transponder (SART) which responds to 9 GHz radar signal, or an Emergency Position-Indicating Radio Beacon (EPIRB) which operates in the 406 MHz radio frequency. EPIRB signals are received and processed by a constellation of satellites known as COSPAS-SARSAT. Older EPIRBs which use 121.5 MHz are obsolete. Many regulators require vessels which proceed offshore to carry an EPIRB.

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Wikipedia