A distress signal, also known as a distress call, is an internationally recognized means for obtaining help. Distress signals are communicated by transmitting
radio
Radio is the technology of signaling and communicating using radio waves. Radio waves are electromagnetic waves of frequency between 30 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transmit ...
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
A ship is a large watercraft that travels the world's oceans and other sufficiently deep waterways, carrying cargo or passengers, or in support of specialized missions, such as defense, research, and fishing. Ships are generally distinguished ...
,
aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air. It counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines ...
, or other vehicle is threatened by a serious or imminent danger and requires immediate assistance.
[Aeronautical Information Manual]
U.S. Federal Aviation Administration, 2016 Use of distress signals in other circumstances may be against local or
international law
International law (also known as public international law and the law of nations) is the set of rules, norms, and standards generally recognized as binding between states. It establishes normative guidelines and a common conceptual framework for ...
. An
urgency signal is available to request assistance in less critical situations.
For distress signalling to be the most effective, two parameters must be communicated:
* Alert or notification of an
emergency
An emergency is an urgent, unexpected, and usually dangerous situation that poses an immediate risk to health, life, property, or environment and requires immediate action. Most emergencies require urgent intervention to prevent a worsening ...
in progress
* Position or location (or localization or pinpointing) of the party in distress.
For example, a single aerial
flare
A flare, also sometimes called a fusée, fusee, or bengala in some Latin-speaking countries, is a type of pyrotechnic that produces a bright light or intense heat without an explosion. Flares are used for distress signaling, illumination, ...
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
An Emergency Position-Indicating Radio Beacon (EPIRB) is a type of emergency locator beacon for commercial and recreational boats, a portable, battery-powered radio transmitter used in emergencies to locate boaters in distress and in need of i ...
both notifies or alerts authorities and at the same time provides position indication information.
Maritime
Distress signals at sea are defined in the
International Regulations for Preventing Collisions at Sea and in the
International Code of Signals
The International Code of Signals (ICS) is an international system of signals and codes for use by vessels to communicate important messages regarding safety of navigation and related matters. Signals can be sent by flaghoist, signal lamp ("bl ...
.
Mayday signals must only be used where there is grave and imminent danger to life. Otherwise, urgent signals such as
pan-pan
The radiotelephony message PAN-PAN is the international standard urgency signal that someone aboard a boat, ship, aircraft, or other vehicle uses to declare that they have a situation that is urgent, but for the time being, does not pose an immed ...
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:
![Smoke signal 1](https://upload.wikimedia.org/wikipedia/commons/3/30/Smoke_signal_1.jpg)
* Transmitting a spoken voice
Mayday message by radio over
very high frequency
Very high frequency (VHF) is the ITU designation for the range of radio frequency electromagnetic waves ( radio waves) from 30 to 300 megahertz (MHz), with corresponding wavelengths of ten meters to one meter.
Frequencies immediately below VHF ...
channel 16 (156.8
MHz
The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose expression in terms of SI base units is s−1, meaning that one he ...
) or
high frequency
High frequency (HF) is the ITU designation for the range of radio frequency electromagnetic waves (radio waves) between 3 and 30 megahertz (MHz). It is also known as the decameter band or decameter wave as its wavelengths range from one to ten ...
on
2182 kHz
* Transmitting a digital distress signal by activating (or pressing) the distress button (or key) on a marine radio equipped with
Digital Selective Calling (DSC) over the VHF (channel 70) or HF frequency bands.
* Transmitting a digital distress signal by activating (or pressing) the distress button (or key) on an
Inmarsat-C
Inmarsat-C is a two-way, packet data service operated by the telecommunications company Inmarsat which operates between mobile earth stations (MES) and land earth stations (LES). It became fully operational after a period of pre-operational trial ...
satellite internet device
* Sending the
Morse code
Morse code is a method used in telecommunication to encode text characters as standardized sequences of two different signal durations, called ''dots'' and ''dashes'', or ''dits'' and ''dahs''. Morse code is named after Samuel Morse, one of ...
group
SOS () by light flashes or sounds
* Burning a red
flare
A flare, also sometimes called a fusée, fusee, or bengala in some Latin-speaking countries, is a type of pyrotechnic that produces a bright light or intense heat without an explosion. Flares are used for distress signaling, illumination, ...
(either hand-held or aerial parachute flare)
* Launching
distress rocket
A flare, also sometimes called a fusée, fusee, or bengala in some Latin-speaking countries, is a type of pyrotechnic that produces a bright light or intense heat without an explosion. Flares are used for distress signaling, illumination, o ...
s
* Emitting orange
smoke
Smoke is a suspension of airborne particulates and gases emitted when a material undergoes combustion or pyrolysis, together with the quantity of air that is entrained or otherwise mixed into the mass. It is commonly an unwanted by-product ...
from a canister
* Showing flames on the vessel (as from a burning tar barrel, oil barrel, etc.)
* Raising and lowering slowly and repeatedly both arms outstretched to each side
* Making a continuous sound with any
fog-signaling apparatus
* Firing a gun or other explosive signal at intervals of about a minute
* Flying the
international maritime signal flags NC
![ICS Charlie](https://upload.wikimedia.org/wikipedia/commons/e/e7/ICS_Charlie.svg)
* Displaying a visual signal consisting of a square flag having above or below it a ball or anything resembling a ball (round or circular in appearance)
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:
* Sea marker dye
* White high-intensity strobe light flashing at 60 times per minute
Automated radio signals
In addition, distress can be signaled using automated radio signals such as a
Search and Rescue Transponder (SART) which response to 9 GHz radar signal, or an
Emergency Position-Indicating Radio Beacon
An Emergency Position-Indicating Radio Beacon (EPIRB) is a type of emergency locator beacon for commercial and recreational boats, a portable, battery-powered radio transmitter used in emergencies to locate boaters in distress and in need of i ...
(EPIRB) which operates in the 406 MHz radiofrequency. EPIRB signals are received and processed by a constellation of satellites known as
Cospas-Sarsat
The International Cospas-Sarsat Programme is a satellite-aided search and rescue (SAR) initiative. It is organized as a treaty-based, nonprofit, intergovernmental, humanitarian cooperative of 45 nations and agencies (see infobox). It is dedi ...
. Older EPIRBs that use 121.5 MHz is obsolete. Many regulators require vessels that proceed offshore to carry an EPIRB.
Many EPIRBs have an in-built Global Positioning System receiver. When activated these EPIRBs rapidly report the latitude and longitude of the emergency accurate to within . The position of non-GPS EPIRBs is determined by the orbiting satellites, this can take ninety minutes to five hours after activation and is accurate to within . Marine safety authorities recommend the use of GPS-equipped EPIRBs.
A miniaturized EPIRB capable of being carried in crew members' clothing is called a Personal Locator Beacon (PLB). Regulators do not view them as a substitute for a vessel's EPIRB. In situations with a high risk of "man overboard", such as open ocean yacht racing, PLBs may be required by the event's organizers. PLBs are also often carried during risky outdoor activities on the land.
EPIRBs and PLBs have a unique identification number (UIN or "HexID"). A purchaser should register their EPIRB or PLB with the national search and rescue authority; this is free in most jurisdictions. EPIRB registration allows the authority to alert searchers of the vessel's name, label, type, size, and paintwork; to promptly notify next-of-kin, and to quickly resolve inadvertent activations.
A DSC radio distress signal can include the position if the lat/long are manually keyed into the radio or if a GPS-derived position is passed electronically directly into the radio.
Mayday
A Mayday message consists of the word "mayday" spoken three times in succession, which is the distress signal, followed by the distress message, which should include:
* Name of the vessel or ship in distress
* Its position (actual, last known, or estimated expressed in lat/long or in distance/bearing from a specific location)
* Nature of the vessel distress condition or situation (e.g. on fire, sinking, aground, taking on water, adrift in hazardous waters)
* Number of persons at risk or to be rescued; grave injuries
* Type of assistance needed or being sought
* Any other details to facilitate resolution of the emergency such as actions being taken (e.g. abandoning ship, pumping flood water), estimated available time remaining afloat
Unusual or extraordinary appearance
When none of the above-described officially sanctioned signals are available, attention for assistance can be attracted by anything that appears unusual or out of the ordinary, such as a
jib sail hoisted upside down.
During daylight hours when the sun is visible, a
heliograph
A heliograph () is a semaphore system that signals by flashes of sunlight (generally using Morse code) reflected by a mirror. The flashes are produced by momentarily pivoting the mirror, or by interrupting the beam with a shutter. The heliograp ...
mirror can be used to flash bright, intense sunlight. Battery-powered laser lights the size of small flashlights (electric torches) are available for use in emergency signaling.
Inverted flags
For hundreds of years inverted
national flag
A national flag is a flag that represents and symbolizes a given nation. It is flown by the government of that nation, but usually can also be flown by its citizens. A national flag is typically designed with specific meanings for its colours ...
s were commonly used as distress signals. However, for some countries' flags it is difficult (e.g.,
Spain
, image_flag = Bandera de España.svg
, image_coat = Escudo de España (mazonado).svg
, national_motto = ''Plus ultra'' (Latin)(English: "Further Beyond")
, national_anthem = (English: "Royal March")
, i ...
,
South Korea
South Korea, officially the Republic of Korea (ROK), is a country in East Asia, constituting the southern part of the Korea, Korean Peninsula and sharing a Korean Demilitarized Zone, land border with North Korea. Its western border is formed ...
,
United Kingdom
The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and North ...
) or impossible (e.g.,
Japan
Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...
,
Thailand
Thailand ( ), historically known as Siam () and officially the Kingdom of Thailand, is a country in Southeast Asia, located at the centre of the Indochinese Peninsula, spanning , with a population of almost 70 million. The country is bo ...
, and
Israel
Israel (; he, יִשְׂרָאֵל, ; ar, إِسْرَائِيل, ), officially the State of Israel ( he, מְדִינַת יִשְׂרָאֵל, label=none, translit=Medīnat Yīsrāʾēl; ), is a country in Western Asia. It is situated ...
) to determine whether they are inverted. Other countries have flags that are inverses of each other; for example, the
Polish
Polish may refer to:
* Anything from or related to Poland, a country in Europe
* Polish language
* Poles
Poles,, ; singular masculine: ''Polak'', singular feminine: ''Polka'' or Polish people, are a West Slavic nation and ethnic group, w ...
flag is white on the top half and red on the bottom, while
Indonesia
Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania between the Indian and Pacific oceans. It consists of over 17,000 islands, including Sumatra, Java, Sulawesi, and parts of Borneo and New Guine ...
's and
Monaco
Monaco (; ), officially the Principality of Monaco (french: Principauté de Monaco; Ligurian: ; oc, Principat de Mónegue), is a sovereign city-state and microstate on the French Riviera a few kilometres west of the Italian region of Lig ...
's flags are the opposite—i.e., top half red, the bottom half white. A ship flying no flags may also be understood to be in distress. For one country, the
Philippines
The Philippines (; fil, Pilipinas, links=no), officially the Republic of the Philippines ( fil, Republika ng Pilipinas, links=no),
* bik, Republika kan Filipinas
* ceb, Republika sa Pilipinas
* cbk, República de Filipinas
* hil, Republ ...
, an inverted flag is a symbol of war rather than distress.
If any flag is available, distress may be indicated by tying a knot in it and then flying it upside-down, making it into a ''
wheft''.
Device loss and disposal
To avoid pointless searches some devices must be reported when lost. This particularly applies to EPIRBs, lifebuoys, rafts, and devices marked with the vessel's name and port.
Expired flares should not be set off, as this indicates distress. Rather, most port authorities offer disposal facilities for expired distress pyrotechnics. In some areas special training events are organized, where the flares can be used safely.
EPIRBs must not be disposed of into general waste as discarded EPIRBs often trigger at the waste disposal facility. In 2013, the majority of EPIRB activations investigated by the Australian Maritime Safety Authority were due to the incorrect disposal of obsolete 121.5 MHz EPIRB beacons.
Aviation
The civilian
aircraft frequency for voice distress alerting is 121.5 MHz. Military aircraft use 243 MHz (which is a
harmonic
A harmonic is a wave with a frequency that is a positive integer multiple of the ''fundamental frequency'', the frequency of the original periodic signal, such as a sinusoidal wave. The original signal is also called the ''1st harmonic'', the ...
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 code
A transponder (short for ''trans''mitter-res''ponder'' and sometimes abbreviated to XPDR, XPNDR, TPDR or TP) is an electronic device that produces a response when it receives a radio-frequency interrogation. Aircraft have transponders to assist ...
s, such as 7700.
The COSPAS/SARSAT signal can be transmitted by an Electronic Locator Transmitter or ELT, which is similar to a marine EPIRB on the 406 MHz radiofrequency. (Marine EPIRBs are constructed to float, while an aviation ELT is constructed to be activated by a sharp deceleration and is sometimes referred to as a Crash Position Indicator or CPI).
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.
Schwarzwald
The recognized mountain distress signals are based on groups of three, or six in the UK and the European Schwarzwald. A distress signal can be three fires or piles of rocks in a triangle, three blasts on a whistle, three shots from a firearm, or three flashes of light, in succession followed by a one-minute pause and repeated until a response is received. Three blasts or flashes is the appropriate response.
In the
Schwarzwald
The Black Forest (german: Schwarzwald ) is a large forested mountain range in the state of Baden-Württemberg in southwest Germany, bounded by the Rhine Valley to the west and south and close to the borders with France and Switzerland. It is t ...
, the recommended way to signal distress is the
Schwarzwald distress signal: give ''six signals within a minute'', then pause for a minute, repeating this until rescue arrives. A signal may be anything visual (waving clothes or lights, use of a
signal mirror) or audible (shouts, whistles, etc.). The rescuers acknowledge with three signals per minute.
In practice, either signal pattern is likely to be recognized in most popular mountainous areas as nearby climbing teams are likely to include Europeans or North Americans.
To communicate with a helicopter in sight, raise both arms (forming the letter Y) to indicate "Yes" or "I need help," or stretch one arm up and one down (imitating the letter N) for "No" or "I do not need help". If
semaphore flags
Flag semaphore (from the Ancient Greek () 'sign' and - (-) '-bearer') is a semaphore system conveying information at a distance by means of visual signals with hand-held flags, rods, disks, paddles, or occasionally bare or gloved hands. Informa ...
are available, they can be used to communicate with rescuers.
Ground beacons
The COSPAS-SARSAT 406 MHz radiofrequency distress signal can be transmitted by
hiker
Hiking is a long, vigorous walk, usually on trails or footpaths in the countryside. Walking for pleasure developed in Europe during the eighteenth century.AMATO, JOSEPH A. "Mind over Foot: Romantic Walking and Rambling." In ''On Foot: A Histor ...
s,
backpackers,
trekkers,
mountaineer
Mountaineering or alpinism, is a set of outdoor activities that involves ascending tall mountains. Mountaineering-related activities include traditional outdoor climbing, skiing, and traversing via ferratas. Indoor climbing, sport climbing, an ...
s and other ground-based remote adventure seekers and personnel working in isolated backcountry areas using a small, portable
Personal Locator Beacon or
PLB.
See also
*
2182 kHz
*
500 kHz
*
COSPAS-SARSAT
The International Cospas-Sarsat Programme is a satellite-aided search and rescue (SAR) initiative. It is organized as a treaty-based, nonprofit, intergovernmental, humanitarian cooperative of 45 nations and agencies (see infobox). It is dedi ...
Search And Rescue Satellite Aided Tracking
*
Digital Selective Calling
Digital selective calling or DSC is a standard for transmitting predefined digital messages via the medium-frequency (MF), high-frequency (HF) and very-high-frequency (VHF) maritime radio systems. It is a core part of the Global Maritime Distres ...
DSC
*
Emergency Alert System
The Emergency Alert System (EAS) is a national warning system in the United States designed to allow authorized officials to broadcast emergency alerts and warning messages to the public via cable, satellite, or broadcast television, and both ...
*
Emergency telephone number
Most public switched telephone networks have a single emergency telephone number (sometimes known as the universal emergency telephone number or the emergency services number) that allows a caller to contact local emergency services for assista ...
*
Global Maritime Distress Safety System
The Global Maritime Distress and Safety System (GMDSS) is a worldwide system for automated emergency signal communication for ships at sea developed by the United Nations' International Maritime Organization (IMO) as part of the SOLAS Convent ...
GMDSS
*
International distress frequency
An international distress frequency is a radio frequency that is designated for emergency communication by international agreement.
History
For much of the 20th century, 500 kHz was the primary international distress frequency. Its use has bee ...
*
Maritime mobile amateur radio
*
Mayday
*
Mountain rescue
Mountain rescue refers to search and rescue activities that occur in a mountainous environment, although the term is sometimes also used to apply to search and rescue in other wilderness environments. This tends to include mountains with tech ...
*
Search and Rescue Transponder
*
SOLAS Convention
The International Convention for the Safety of Life at Sea (SOLAS) is an international maritime treaty that sets minimum safety standards in the construction, equipment and operation of merchant ships. The International Maritime Organization ...
*
SOS
*
Vessel emergency codes
In addition to distress signals like Mayday and pan-pan, most vessels, especially passenger ships, use some emergency signals to alert the crew on board. In some cases, the signals may alert the passengers to danger, but, in others, the objective ...
*
Emergency locator beacon
An emergency locator beacon is a radio beacon, a portable battery powered radio transmitter, used to locate airplanes, vessels, and persons in distress and in need of immediate rescue. Various types of emergency locator beacons are carried by airc ...
References
External links
What is the meaning of SOS?*
ttp://www.uscg.mil/hq/g-m/mse4/vds.htm US Coast Guard: Flares and other Visual Distress SignalsTransport Canada: Radio Distress Procedures Card
{{Authority control
Emergency communication
Encodings
Maritime signalling
Rescue
Survival skills