In radiotelegraphy, the safety signal consist of three repetitions of the group TTT, the individual letters of each group and the successive group being clearly separated from each other. It shall be sent before the call.
In radiotelephony, the safety signal consist of the word “SECURITE” pronounced clearly as in French, spoken three times and transmitted before the call.
This safety signal indicates that the station is about to transmit a message containing an important navigation or important meteorological warning. Safety signal and call shall be sent on or more of the international distress frequencies (500, 2182 khz,156.8) Mhz or any other frequency which may be used in case of distress.
The safety message which follows the call should be sent on a working frequency. A suitable announcement to this effect shall be made at he end of the call. In the maritime mobile service, safety messages shall generally be addressed to all stations. In some cases, however, they may be addressed to a particular station. All stations hearing the safety signal shall listen to the safety message until they are satisfied that the message is of no concern to them. They shall not make any transmission likely to interfere with the message.
Wednesday, November 12, 2008
Friday, November 7, 2008
ACKNOWLEDGEMENT OF RECEIPT OF A DISTRESS MESSAGE
1. Stations of the mobile service which receive a distress message from a mobile station which is, beyond any possible doubt in their vicinity, shall immediately acknowledge receipt.
2. However, in areas where reliable communications with one or more coast stations are practicable. Ship station should defer this acknowledgement for a short interval so that a coast station may be acknowledge receipt.
3. Station of the mobile service which receive a distress message from a mobile station which, beyond any possible doubt, is not in their vicinity, shall allow a short interval of time to elapse before acknowledging receipt of the message, in order to permit stations nearer to the mobile station in distress to acknowledge receipt without interference.
4. However, stations in the marine service which receive a distress message from a mobile station which, beyond any possible doubt, is a long distance away need not acknowledge receipt of messages except as specified.
THE ACKNOWLEDGEMENT OF RECEIPT OF A DISTRESS MESSAGE SHALL BE GIVEN IN THE FOLLOWING FORM:
a) RADIOTELEGRAPHY:
*the distress signal SOS
*the call sign of the station sending the distress message, sent three times
*the word DE
*the distress signal SOS
b) RADIOTELEPHONY:
*the distress signal MAYDAY
*the call sigh sending the distress message, spoken 3 times
*the word THIS IS or DE spoken as DELTA ECHO in case of language difficulties
*the call sign or other identification of the station acknowledging the message, spoken three times.
*the word RECEIVED (or RRR spoken as ROMEO ROMEO ROMEO in case of language difficulties)
*the distress signal MAYDAY
2. However, in areas where reliable communications with one or more coast stations are practicable. Ship station should defer this acknowledgement for a short interval so that a coast station may be acknowledge receipt.
3. Station of the mobile service which receive a distress message from a mobile station which, beyond any possible doubt, is not in their vicinity, shall allow a short interval of time to elapse before acknowledging receipt of the message, in order to permit stations nearer to the mobile station in distress to acknowledge receipt without interference.
4. However, stations in the marine service which receive a distress message from a mobile station which, beyond any possible doubt, is a long distance away need not acknowledge receipt of messages except as specified.
THE ACKNOWLEDGEMENT OF RECEIPT OF A DISTRESS MESSAGE SHALL BE GIVEN IN THE FOLLOWING FORM:
a) RADIOTELEGRAPHY:
*the distress signal SOS
*the call sign of the station sending the distress message, sent three times
*the word DE
*the distress signal SOS
b) RADIOTELEPHONY:
*the distress signal MAYDAY
*the call sigh sending the distress message, spoken 3 times
*the word THIS IS or DE spoken as DELTA ECHO in case of language difficulties
*the call sign or other identification of the station acknowledging the message, spoken three times.
*the word RECEIVED (or RRR spoken as ROMEO ROMEO ROMEO in case of language difficulties)
*the distress signal MAYDAY
General Radiotelephone Emergency Communications
Emergency Conditions
Emergency conditions are classified in accordance with the degree of danger or hazard as follows:
Distress: A condition of being threatened by grave and/or imminent danger and requiring immediate assistance.
Urgency: A condition concerning the safety of an aircraft or other vehicle, or of someone on board or within sight, but which does not require immediate assistance.
Safety: An indication that the station calling is about to transmit a message concerning the safety of navigation or important meteorological warnings.
Distress, urgency and safety procedures are outlined in regulations and are designed primarily for the aeronautical and maritime services. Use of these types of communications in the land mobile service is very rare.
Since detailed procedures for distress, urgency and safety communications have not been expressly developed for use in the land-mobile service, a brief outline of procedures for providing safety-related communications is given in the following sections.
* Distress Communications
Distress communications should be conducted in accordance with the procedures outlined in this section. These procedures shall not, however, prevent a station in distress from making use of any means at its disposal to attract attention, to make known its position, and to obtain assistance.
* Frequencies to Be Used
The first transmission of the distress call and message by a station should be made on the frequency in use at the time. If the station is unable to establish communications on the frequency in use, the distress call and message should be repeated on any other frequency available in an effort to establish communications with any other station.
* Distress Signal
In radiotelephony, the spoken word for distress is "MAYDAY", and it should be used at the commencement of the first distress communication.
The distress signal indicates that a person or station sending the signal is:
1. threatened by grave and imminent danger and requires immediate assistance, or
2. aware that an aircraft, ship, other station or person is threatened by grave and imminent danger and requires immediate assistance.
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Priority of Distress
The distress call has absolute priority over all other transmissions. All stations which hear it shall immediately cease any transmission capable of interfering with distress traffic and continue to listen on the frequency used for the distress call.
* Control of Distress Traffic
The control of distress traffic is the responsibility of the station in distress or of the station which relays the distress message. These stations may, however, delegate the control of distress traffic to another station.
* Distress Call
The distress call identifies the station in distress, and such calls shall only be sent on the authority of the person in command of the station. The distress call should comprise:
1. the distress signal "MAYDAY" spoken three times;
2. the words "THIS IS";
3. the call sign of the station in distress spoken three times.
Example:
MAYDAY, MAYDAY, MAYDAY
THIS IS
PIPER CHARLIE FOXTROT X-RAY QUEBEC QUEBEC
PIPER CHARLIE FOXTROT X-RAY QUEBEC QUEBEC
PIPER CHARLIE FOXTROT X-RAY QUEBEC QUEBEC
The distress call shall not be addressed to a particular station and acknowledgement of receipt shall not be given before the distress message is sent.
* Distress Message
The distress message shall follow the distress call as soon as possible.
The distress message should include as many as possible of the following elements spoken distinctly and, if possible, in the following order:
1. the distress signal "MAYDAY";
2. the call of the sign station in distress (once);
3. the nature of the distress condition and the kind of assistance required (i.e. what has happened);
4. the intentions of the person in command;
5. the particulars of its position (location, airspeed, altitude, heading);
6. the number of persons on board and injuries (if applicable);
7. any other information that might facilitate the rescue;
8. the call sign of the station in distress.
Example: MAYDAY
PIPER CHARLIE FOXTROT X-RAY QUEBEC QUEBEC
STRUCK BY LIGHTNING
DITCHING AIRCRAFT
POSITION: 20 MILES EAST OF WINNIPEG
ALTITUDE: 1500 FEET
AIRSPEED: 125 KNOTS
HEADING: 270 T
ONE PERSON ON BOARD
PIPER CHARLIE FOXTROT X-RAY QUEBEC QUEBEC
Note: If the station operator can transmit the distress message immediately after the distress call, then items 1 and 2 may be omitted from the message.
* Repetition of a Distress Message
The distress message shall be repeated at intervals by the station in distress until an answer is received or until it is no longer feasible to continue. The intervals between repetitions of the distress message shall be sufficiently long enough to allow time for stations receiving the message to reply.
Any station that has heard an unacknowledged distress message and is not in a position to render assistance, shall take all possible steps to attract the attention of other stations that are in a position to assist.
In addition, all necessary steps shall be taken to notify the appropriate search and rescue authorities of the situation.
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* Action by Station in Distress
When a station is threatened by grave and imminent danger, and requires immediate assistance, the person in command should direct appropriate action as follows:
1. transmit the distress call;
2. transmit the distress message;
3. listen for acknowledgement of receipt;
4. exchange further distress traffic as applicable;
5. activate automatic emergency equipment (emergency locator transmitter - ELT) if available and when appropriate.
* Action by Stations Other than the Station in Distress
A station that is not in distress should transmit the distress message when:
1. the station in distress is not in a position to transmit the message, or
2. the person in command of the station that intervenes believes that further help is necessary.
When a distress message is received and it is known that the affected station is not in the immediate vicinity, sufficient time should be allowed before the distress message is acknowledged. This will permit stations nearer to the station in distress to reply.
* Action by Other Stations Hearing a Distress Message
1. Continue to monitor the frequency on which the distress message was received and, if possible, establish a continuous watch on appropriate distress and emergency frequencies.
2. Notify any station with direction-finding or radar facilities and request assistance unless it is known that this action has been, or will be, taken by the station acknowledging receipt of the distress message.
3. Cease all transmissions that may interfere with the distress traffic.
* Distress Traffic
Distress traffic consists of all transmissions relative to the immediate assistance required by the station in distress. Essentially, all transmissions made after the initial distress call are considered as distress traffic. In distress traffic, the distress signal "MAYDAY" spoken once, shall precede all transmissions. This procedure is intended to alert stations not aware of the initial distress call and now monitoring the distress channel that traffic heard relates to a distress situation.
Any station in the land mobile, aeronautical, or maritime mobile service that has knowledge of distress traffic and cannot itself assist the station in distress shall follow such traffic until it is evident that assistance is being provided. All stations that are aware of distress traffic, and that are not taking part in it, are forbidden to transmit on the frequencies being used for distress traffic until a message is received indicating that normal working traffic may be resumed (cancellation of distress).
5.2.12 Acknowledgement of Receipt of a Distress Message
The acknowledgement of receipt of a distress message shall be given in the following form:
1. the distress signal "MAYDAY"
2. the call sign of the station in distress (spoken three times);
3. the words "THIS IS";
4. 4. the call sign of the station acknowledging receipt (spoken three times);
5. the words "RECEIVED MAYDAY".
Example: MAYDAY
PIPER CHARLIE FOXTROT X-RAY QUEBEC QUEBEC
PIPER CHARLIE FOXTROT X-RAY QUEBEC QUEBEC
PIPER CHARLIE FOXTROT X-RAY QUEBEC QUEBEC
THIS IS WINNIPEG TOWER
WINNIPEG TOWER
WINNIPEG TOWER
RECEIVED MAYDAY
5.2.13 Action by Stations Acknowledging Receipt of a Distress Message
1. Forward information immediately to the appropriate search and rescue agencies or organizations.
2. Continue to monitor the frequency on which the distress message was received and, if possible, any other frequency that may be used by the station in distress.
3. Notify any station with direction-finding or radar facilities that may be of assistance, etc.
4. Cease all transmissions that may interfere with the distress traffic.
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Relay of a Distress Message
A distress message repeated by a station other than the station in distress shall transmit a signal comprised of:
1. the signal "MAYDAY RELAY" (spoken three times);
2. the words "THIS IS";
3. the call sign of the station relaying the message (spoken three times);
4. the distress signal "MAYDAY" (once);
5. the particulars of the station in distress such as its location, the nature of distress, the number of persons on board, etc.
Example: MAYDAY RELAY, MAYDAY RELAY, MAYDAY RELAY
THIS IS
CESSNA CHARLIE NOVEMBER JULIETT INDIA
CESSNA CHARLIE NOVEMBER JULIETT INDIA
CESSNA CHARLIE NOVEMBER JULIETT INDIA
MAYDAY
PIPER CHARLIE FOXTROT X-RAY QUEBEC QUEBEC
STRUCK BY LIGHTNING
DITCHING AIRCRAFT
POSITION: 20 MILES EAST OF WINNIPEG
ALTITUDE: 1500 FEET
AIRSPEED: 125 KNOTS
HEADING: 270 DEGREES
ONE PERSON ON BOARD
PIPER CHARLIE FOXTROT X-RAY QUEBEC QUEBEC
* Imposition of Silence
The station in distress, or the station in control of distress traffic, may impose silence on all stations in the area or on any station that interferes with the distress traffic. It shall address these instructions to "all stations", or to one station only as appropriate.
The station in distress, or the station in control, shall use the expression "SEELONCE MAYDAY".
If it is believed to be essential, other stations near the station in distress may also impose silence during a distress situation by using the international expression "SEELONCE DISTRESS".
Should radio silence be imposed during a distress situation, all transmissions shall cease immediately except for those stations involved in distress traffic.
Examples: Imposition of silence on a specific station by the station in distress.
(Cessna C-FNJI is causing interference to distress traffic.)
CESSNA CHARLIE FOXTROT NOVEMBER JULIETT INDIA
THIS IS
PIPER CHARLIE FOXTROT X-RAY QUEBEC QUEBEC
SEELONCE MAYDAY
OUT
Imposition of silence on all stations by a station other than the station in distress.
ALL STATIONS, ALL STATIONS, ALL STATIONS
THIS IS
CESSNA CHARLIE FOXTROT NOVEMBER JULIETT INDIA
SEELONCE DISTRESS
OUT
* Cancellation of Distress
When a station is no longer in distress, or when it is no longer necessary to observe radio silence (i.e. the rescue operation has concluded), the station that controlled the distress traffic shall transmit a message addressed to "ALL STATIONS" on the distress frequency(ies) used, advising that normal operation may resume. The proper procedure for cancelling a distress message is:
1. the distress signal "MAYDAY" (once);
2. the words "HELLO ALL STATIONS" (three times);
3. the words "THIS IS";
4. the name or call sign of the station transmitting the message;
5. the filing time of the message;
6. the call sign of the station in distress (once);
7. the words "SEELONCE FEENEE";
Example:
MAYDAY
HELLO ALL STATIONS, HELLO ALL STATIONS, HELLO ALL STATIONS
THIS IS
WINNIPEG TOWER
TIME 1630 ZULU
PIPER CHARLIE FOXTROT X-RAY QUEBEC QUEBEC
SEELONCE FEENEE
OUT
Note: The procedure outlined above is mainly for the benefit of other stations so they can resume regular service. To ensure that search and rescue stations are advised that a station is no longer in distress, a normal call to the nearest rescue coordination centre detailing the reasons for cancelling the distress call MUST be made.
Emergency conditions are classified in accordance with the degree of danger or hazard as follows:
Distress: A condition of being threatened by grave and/or imminent danger and requiring immediate assistance.
Urgency: A condition concerning the safety of an aircraft or other vehicle, or of someone on board or within sight, but which does not require immediate assistance.
Safety: An indication that the station calling is about to transmit a message concerning the safety of navigation or important meteorological warnings.
Distress, urgency and safety procedures are outlined in regulations and are designed primarily for the aeronautical and maritime services. Use of these types of communications in the land mobile service is very rare.
Since detailed procedures for distress, urgency and safety communications have not been expressly developed for use in the land-mobile service, a brief outline of procedures for providing safety-related communications is given in the following sections.
* Distress Communications
Distress communications should be conducted in accordance with the procedures outlined in this section. These procedures shall not, however, prevent a station in distress from making use of any means at its disposal to attract attention, to make known its position, and to obtain assistance.
* Frequencies to Be Used
The first transmission of the distress call and message by a station should be made on the frequency in use at the time. If the station is unable to establish communications on the frequency in use, the distress call and message should be repeated on any other frequency available in an effort to establish communications with any other station.
* Distress Signal
In radiotelephony, the spoken word for distress is "MAYDAY", and it should be used at the commencement of the first distress communication.
The distress signal indicates that a person or station sending the signal is:
1. threatened by grave and imminent danger and requires immediate assistance, or
2. aware that an aircraft, ship, other station or person is threatened by grave and imminent danger and requires immediate assistance.
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Priority of Distress
The distress call has absolute priority over all other transmissions. All stations which hear it shall immediately cease any transmission capable of interfering with distress traffic and continue to listen on the frequency used for the distress call.
* Control of Distress Traffic
The control of distress traffic is the responsibility of the station in distress or of the station which relays the distress message. These stations may, however, delegate the control of distress traffic to another station.
* Distress Call
The distress call identifies the station in distress, and such calls shall only be sent on the authority of the person in command of the station. The distress call should comprise:
1. the distress signal "MAYDAY" spoken three times;
2. the words "THIS IS";
3. the call sign of the station in distress spoken three times.
Example:
MAYDAY, MAYDAY, MAYDAY
THIS IS
PIPER CHARLIE FOXTROT X-RAY QUEBEC QUEBEC
PIPER CHARLIE FOXTROT X-RAY QUEBEC QUEBEC
PIPER CHARLIE FOXTROT X-RAY QUEBEC QUEBEC
The distress call shall not be addressed to a particular station and acknowledgement of receipt shall not be given before the distress message is sent.
* Distress Message
The distress message shall follow the distress call as soon as possible.
The distress message should include as many as possible of the following elements spoken distinctly and, if possible, in the following order:
1. the distress signal "MAYDAY";
2. the call of the sign station in distress (once);
3. the nature of the distress condition and the kind of assistance required (i.e. what has happened);
4. the intentions of the person in command;
5. the particulars of its position (location, airspeed, altitude, heading);
6. the number of persons on board and injuries (if applicable);
7. any other information that might facilitate the rescue;
8. the call sign of the station in distress.
Example: MAYDAY
PIPER CHARLIE FOXTROT X-RAY QUEBEC QUEBEC
STRUCK BY LIGHTNING
DITCHING AIRCRAFT
POSITION: 20 MILES EAST OF WINNIPEG
ALTITUDE: 1500 FEET
AIRSPEED: 125 KNOTS
HEADING: 270 T
ONE PERSON ON BOARD
PIPER CHARLIE FOXTROT X-RAY QUEBEC QUEBEC
Note: If the station operator can transmit the distress message immediately after the distress call, then items 1 and 2 may be omitted from the message.
* Repetition of a Distress Message
The distress message shall be repeated at intervals by the station in distress until an answer is received or until it is no longer feasible to continue. The intervals between repetitions of the distress message shall be sufficiently long enough to allow time for stations receiving the message to reply.
Any station that has heard an unacknowledged distress message and is not in a position to render assistance, shall take all possible steps to attract the attention of other stations that are in a position to assist.
In addition, all necessary steps shall be taken to notify the appropriate search and rescue authorities of the situation.
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Top of Page
* Action by Station in Distress
When a station is threatened by grave and imminent danger, and requires immediate assistance, the person in command should direct appropriate action as follows:
1. transmit the distress call;
2. transmit the distress message;
3. listen for acknowledgement of receipt;
4. exchange further distress traffic as applicable;
5. activate automatic emergency equipment (emergency locator transmitter - ELT) if available and when appropriate.
* Action by Stations Other than the Station in Distress
A station that is not in distress should transmit the distress message when:
1. the station in distress is not in a position to transmit the message, or
2. the person in command of the station that intervenes believes that further help is necessary.
When a distress message is received and it is known that the affected station is not in the immediate vicinity, sufficient time should be allowed before the distress message is acknowledged. This will permit stations nearer to the station in distress to reply.
* Action by Other Stations Hearing a Distress Message
1. Continue to monitor the frequency on which the distress message was received and, if possible, establish a continuous watch on appropriate distress and emergency frequencies.
2. Notify any station with direction-finding or radar facilities and request assistance unless it is known that this action has been, or will be, taken by the station acknowledging receipt of the distress message.
3. Cease all transmissions that may interfere with the distress traffic.
* Distress Traffic
Distress traffic consists of all transmissions relative to the immediate assistance required by the station in distress. Essentially, all transmissions made after the initial distress call are considered as distress traffic. In distress traffic, the distress signal "MAYDAY" spoken once, shall precede all transmissions. This procedure is intended to alert stations not aware of the initial distress call and now monitoring the distress channel that traffic heard relates to a distress situation.
Any station in the land mobile, aeronautical, or maritime mobile service that has knowledge of distress traffic and cannot itself assist the station in distress shall follow such traffic until it is evident that assistance is being provided. All stations that are aware of distress traffic, and that are not taking part in it, are forbidden to transmit on the frequencies being used for distress traffic until a message is received indicating that normal working traffic may be resumed (cancellation of distress).
5.2.12 Acknowledgement of Receipt of a Distress Message
The acknowledgement of receipt of a distress message shall be given in the following form:
1. the distress signal "MAYDAY"
2. the call sign of the station in distress (spoken three times);
3. the words "THIS IS";
4. 4. the call sign of the station acknowledging receipt (spoken three times);
5. the words "RECEIVED MAYDAY".
Example: MAYDAY
PIPER CHARLIE FOXTROT X-RAY QUEBEC QUEBEC
PIPER CHARLIE FOXTROT X-RAY QUEBEC QUEBEC
PIPER CHARLIE FOXTROT X-RAY QUEBEC QUEBEC
THIS IS WINNIPEG TOWER
WINNIPEG TOWER
WINNIPEG TOWER
RECEIVED MAYDAY
5.2.13 Action by Stations Acknowledging Receipt of a Distress Message
1. Forward information immediately to the appropriate search and rescue agencies or organizations.
2. Continue to monitor the frequency on which the distress message was received and, if possible, any other frequency that may be used by the station in distress.
3. Notify any station with direction-finding or radar facilities that may be of assistance, etc.
4. Cease all transmissions that may interfere with the distress traffic.
Return to Top of Page
Top of Page
Relay of a Distress Message
A distress message repeated by a station other than the station in distress shall transmit a signal comprised of:
1. the signal "MAYDAY RELAY" (spoken three times);
2. the words "THIS IS";
3. the call sign of the station relaying the message (spoken three times);
4. the distress signal "MAYDAY" (once);
5. the particulars of the station in distress such as its location, the nature of distress, the number of persons on board, etc.
Example: MAYDAY RELAY, MAYDAY RELAY, MAYDAY RELAY
THIS IS
CESSNA CHARLIE NOVEMBER JULIETT INDIA
CESSNA CHARLIE NOVEMBER JULIETT INDIA
CESSNA CHARLIE NOVEMBER JULIETT INDIA
MAYDAY
PIPER CHARLIE FOXTROT X-RAY QUEBEC QUEBEC
STRUCK BY LIGHTNING
DITCHING AIRCRAFT
POSITION: 20 MILES EAST OF WINNIPEG
ALTITUDE: 1500 FEET
AIRSPEED: 125 KNOTS
HEADING: 270 DEGREES
ONE PERSON ON BOARD
PIPER CHARLIE FOXTROT X-RAY QUEBEC QUEBEC
* Imposition of Silence
The station in distress, or the station in control of distress traffic, may impose silence on all stations in the area or on any station that interferes with the distress traffic. It shall address these instructions to "all stations", or to one station only as appropriate.
The station in distress, or the station in control, shall use the expression "SEELONCE MAYDAY".
If it is believed to be essential, other stations near the station in distress may also impose silence during a distress situation by using the international expression "SEELONCE DISTRESS".
Should radio silence be imposed during a distress situation, all transmissions shall cease immediately except for those stations involved in distress traffic.
Examples: Imposition of silence on a specific station by the station in distress.
(Cessna C-FNJI is causing interference to distress traffic.)
CESSNA CHARLIE FOXTROT NOVEMBER JULIETT INDIA
THIS IS
PIPER CHARLIE FOXTROT X-RAY QUEBEC QUEBEC
SEELONCE MAYDAY
OUT
Imposition of silence on all stations by a station other than the station in distress.
ALL STATIONS, ALL STATIONS, ALL STATIONS
THIS IS
CESSNA CHARLIE FOXTROT NOVEMBER JULIETT INDIA
SEELONCE DISTRESS
OUT
* Cancellation of Distress
When a station is no longer in distress, or when it is no longer necessary to observe radio silence (i.e. the rescue operation has concluded), the station that controlled the distress traffic shall transmit a message addressed to "ALL STATIONS" on the distress frequency(ies) used, advising that normal operation may resume. The proper procedure for cancelling a distress message is:
1. the distress signal "MAYDAY" (once);
2. the words "HELLO ALL STATIONS" (three times);
3. the words "THIS IS";
4. the name or call sign of the station transmitting the message;
5. the filing time of the message;
6. the call sign of the station in distress (once);
7. the words "SEELONCE FEENEE";
Example:
MAYDAY
HELLO ALL STATIONS, HELLO ALL STATIONS, HELLO ALL STATIONS
THIS IS
WINNIPEG TOWER
TIME 1630 ZULU
PIPER CHARLIE FOXTROT X-RAY QUEBEC QUEBEC
SEELONCE FEENEE
OUT
Note: The procedure outlined above is mainly for the benefit of other stations so they can resume regular service. To ensure that search and rescue stations are advised that a station is no longer in distress, a normal call to the nearest rescue coordination centre detailing the reasons for cancelling the distress call MUST be made.
MARINE RADIOTELEPHONE
The Marine Radiotelephone Service or HF ship-to-shore operates on shortwave radio frequencies, using single-sideband modulation. The usual method is that a ship calls a shore station, and the shore station's marine operator connects the caller to the public switched telephone network. This service is retained for safety reasons, but in practice has been made obsolete by satellite telephones, particularly INMARSAT.
Short wave radio is used because it bounces between the ionosphere and the ground, giving a modest 1,000 watt transmitter (the standard power) a world-wide range.
Most shore stations monitor several frequencies. The frequencies with the longest range are usually near 20 MHz, but the ionospheric weather (propagation) can dramatically change which frequencies work best.
Single-sideband (SSB) is used because the short wave bands are crowded with many users, and SSB permits a single voice channel to use a narrower range of radio frequencies (bandwidth), about 3.5 kHz. In comparison, AM radio uses about 8 kHz, and narrowband (voice or communication-quality) FM uses 9 kHz.
Marine radiotelephony first became common in the 1930s, and was used extensively for communications to ships and aircraft over water. In that time, most long-range aircraft had long-wire antennas that would be let out during a call, and reeled-in afterward.
One of the most important uses of marine radiotelephony has been to change ships' itineraries, and to perform other business at sea.
Some ships, including almost all military ships, carry teletypewriters, and use them to communicate over short wave. This is called "marine radiotelegraphy", but in practice the equipment is a normal shortwave radio with an attachment that generates and receives audio tones in order to drive the teletype.
Short wave radio is used because it bounces between the ionosphere and the ground, giving a modest 1,000 watt transmitter (the standard power) a world-wide range.
Most shore stations monitor several frequencies. The frequencies with the longest range are usually near 20 MHz, but the ionospheric weather (propagation) can dramatically change which frequencies work best.
Single-sideband (SSB) is used because the short wave bands are crowded with many users, and SSB permits a single voice channel to use a narrower range of radio frequencies (bandwidth), about 3.5 kHz. In comparison, AM radio uses about 8 kHz, and narrowband (voice or communication-quality) FM uses 9 kHz.
Marine radiotelephony first became common in the 1930s, and was used extensively for communications to ships and aircraft over water. In that time, most long-range aircraft had long-wire antennas that would be let out during a call, and reeled-in afterward.
One of the most important uses of marine radiotelephony has been to change ships' itineraries, and to perform other business at sea.
Some ships, including almost all military ships, carry teletypewriters, and use them to communicate over short wave. This is called "marine radiotelegraphy", but in practice the equipment is a normal shortwave radio with an attachment that generates and receives audio tones in order to drive the teletype.
Thursday, November 6, 2008
MAYDAY (DISTRESS CALL)
A Mayday situation is one in which a vessel, aircraft, vehicle, or person is in grave and imminent danger and requires immediate assistance. Examples of "grave and imminent danger" in which a mayday call would be appropriate include fire, explosion or sinking.
Mayday calls can be made on any frequency, and when a mayday call is made no other radio traffic is permitted except to assist in the emergency. A mayday call may only be made when life or craft is in imminent danger of death or destruction.
'Mayday' calls are made by radio, such as a ship or aircraft's VHF radio. Although a Mayday call will be understood regardless of the radio frequency on which it is broadcast, first-line response organisations, such as the coastguard and air traffic control, monitor designated channels: marine MF on 2182 kHz; marine VHF radio channel 16 (156.8 MHz); and airband frequencies of 121.5 MHz and 243.0 MHz. A Mayday call is roughly equivalent of a morse code SOS, or a telephone call to the emergency services.
When they receive a Mayday call the coastguard may launch lifeboats and helicopters to assist the ship that is in trouble. Other ships that are nearby may divert course to assist the vessel broadcasting the Mayday.
Making a hoax Mayday call is a criminal act in many countries because of the danger to the rescuers' lives that a search-and-rescue operation can create, as well as the very high costs of such rescue efforts. For example, making a false distress call in the U.S. is a federal crime carrying sanctions of up to six years imprisonment, and a fine of $250,000[2].
The coastguard can be contacted in situations that are not emergencies (out of fuel, etc.) by calling 'Coastguard, Coastguard, Coastguard, this is (name of vessel)', on VHF channel 16. In many countries special training and a licence are required to use a mobile radio transmitter legally, although anyone may legally use one to summon help in a real emergency.
The recommended distress call format includes the word MAYDAY spoken three times (repeated twice), followed by the vessel's name or callsign, also spoken three times, then MAYDAY and the name or callsign again. Vital information, including the position, nature of the emergency, assistance required and the number of people on board, should follow. A typical message might be:
"MAYDAY, MAYDAY, MAYDAY, this is NONSUCH, NONSUCH, NONSUCH. MAYDAY, NONSUCH. Position 54 25 North 016 33 West. My boat is on fire and sinking. I require immediate assistance. 4 people on board, are taking a lifeboat. OVER."
If a Mayday call cannot be sent because a radio is not available a variety of other distress signals and calls for help can be used. A Mayday can be sent on behalf of one vessel by another, using a convention called a Mayday Relay.
MAYDAY RELAY CALL
A Mayday relay call is made by one vessel on behalf of a different vessel which is in distress. If a vessel makes a Mayday call and it is not acknowledged by the coastguard after a single repetition and a two-minute wait a vessel receiving the Mayday call should attempt to contact the coastguard on behalf of the Mayday vessel by broadcasting a Mayday Relay on their behalf.
A Mayday Relay call should use the callsign of the transmitting vessel but give the name and position of the Mayday vessel.
Mayday Relay calls can be used to summon help for a vessel which is either too far offshore to contact the coastguard directly or without radio capabilities (though most vessels above a certain size or crew complement are legally required to carry two-way radio equipment, such equipment can potentially be damaged or destroyed).
MOUNTAIN DISTRESS SIGNAL
The recognised mountain distress signals are based on groups of three (six in the UK). A distress signal can be 3 fires or piles of rocks in a triangle, three blasts on a whistle, or three flashes of a 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 Alps, the recommended way to signal distress is the Alpine 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. To communicate with a helicopter in sight, raise both arms (forming the letter Y) to indicate "Yes" or "I need help" and stretch one arm up and one down (imitating the letter N) for "No" or "I do not need help". If semaphore flags are available, they can possibly be used to communicate with rescuers.
DISTRESS SIGNAL
AUTOMATIC DISTRESS SIGNAL UNIT
The radiotelegraphic distress signal consist of the group SOS, transmitted as a single signal in which the dashes are emphasized clearly from dots.
The radiotelephone distress signal consist of the word "MAYDAY" pronounced as the French expression "M'aider".
These distress signal indicate that a ship, aircraft or other vehicle is threatened by grave and imminent danger and request immediate assistance.
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