Distress signal
A distress signal is an internationally recognized means of obtaining help. Distress signals are commonly made by using a radio, displaying a visual object, or making noise from a distance.
A distress signal indicates that a ship, aircraft, or other vehicle is threatened by grave and imminent danger and requests immediate assistance. Use of distress signals in other circumstances may be against local or international law.
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Maritime distress signals
Distress signals at sea are defined in the International Regulations for Preventing Collisions at Sea and in the International Code of Signals. They must only be used where there is grave and imminent danger to life. Other urgent signals should be sent using a pan-pan message.
Distress can be signaled by any of the following means:
- sending a Mayday message by radio on VHF channel 16 (156.8 MHz) or HF on 2182 kHz
- sending the Morse code group SOS
- using red flares (either hand-held or parachute flares)
- emitting orange smoke from a canister
- showing flames on the vessel (as from a burning tar barrel, oil barrel, etc)
- slowly and repeatedly raising and lowering arms outstretched to each side
- a continuous sounding with any fog-signaling apparatus
- a gun or other explosive signal fired at intervals of about a minute
- the International maritime signal flags NC
- a signal consisting of a square flag having above or below it a ball or anything resembling a ball
In addition, distress can be signaled using automated radio signals, eg from an Emergency Position-Indicating Radio Beacon (EPIRB).
If none of the above are available, attention can be drawn by anything unusual, e.g., a jib sail hoisted upside down.
Inverted national flags are no longer commonly used upside as distress signals. It is difficult or impossible to determine when the flags of many countries (such as 
Austria or 
Argentina) are inverted, or the viewer may not be familiar with the flag and may not realize it is not upright. If a national flag is all that is available, distress may be indicated by tying a knot in it, making it into a wheft[1].
Aviation distress signals
The civilian aircraft emergency frequency is 121.5 MHz. Military aircraft use 243 MHz (which is a harmonic of 121.5 MHz, and therefore civilian beacons transmit on this frequency as well). Aircraft can also signal an emergency by setting one of several special transponder codes, such as 7700.
A "triangular distress pattern" is a rarely-used flight pattern flown by aircraft in distress but without radio communications. The standard pattern is a series of 120° turns.
Mountain distress signals
The recognised mountain distress signal is six blasts on a whistle, or six flashes of a light, in succession followed by a one minute pause and repeated until you get a response. Three blasts or flashes is the appropriate response.
See also
- Call for help
- Mayday (distress signal)
- Vessel emergency codes
- Emergency locator transmitter for aircraft
- Emergency Position-Indicating Radio Beacon (EPIRB)
- Global Maritime Distress Safety System
- 500 kHz
- Emergency Alert System
- Mountain rescue
- Maritime mobile amateur radio
External links
- What is the meaning of SOS?
- US Coast Guard: Visual Distress Signals for Recreational Boaters
- US Coast Guard: Flares and other Visual Distress Signals
Categories
Rescue | Survival skills | Encodings | Emergency communication