GMDSS and VHF Distress Procedures

What the rule requires

The proword is settled before you key the mike

The placard language draws the line in one clause: MAYDAY—MAYDAY—MAYDAY is for situations involving immediate danger to life and property, and PAN—PAN—PAN is for urgent situations where there is no immediate danger to life or property 46 CFR §184.510. Nothing else in the procedure turns on which one you chose. The same fourteen steps follow either way, and step 6 simply substitutes whichever proword you opened with alongside the vessel's name.

Classify first, then transmit. A candidate who works it the other way round writes the message and then reaches for a proword to match its tone.

Your main engine has failed six miles offshore in light air, you are drifting in open water clear of hazards, and you want the Coast Guard to know. Which proword?

PAN—PAN—PAN. The situation is urgent but there is no immediate danger to life or property, which is the operative distinction in . Change one fact — set the vessel drifting onto a rocky lee shore with passengers aboard — and immediate danger to life and property exists, so it becomes MAYDAY.

Where the transmission goes

Select 156.8 MHz (channel 16 VHF) or 2182 kHz; both are for emergency and calling purposes only . The fishing-industry version of the same instruction adds a third option worth knowing for an offshore question — 156.8 MHz, 2182 kHz, or other distress frequency used in your area of operation 46 CFR §28.265.

A DSC distress alert is a different transmission on a different frequency. It goes out on VHF channel 70, or on MF/HF at 2187.5 kHz, 8414.5 kHz, 4207.5 kHz, 6312 kHz, 12577 kHz or 16804.5 kHz 33 CFR §87.01. The identical list sits in the International rules at COLREGs Rule 38(l), so an open-book candidate can find it in either volume.

The message, in order

MIPDANIO is the device in general circulation and it is worth using: Mayday, Identity, Position, Distress, Assistance, Number, Information, Over. It cues the sequence in the right order and it will get you through a spoken transmission under pressure.

Where it is lossy is in what it packs into "Information". The placard sequence names four items the mnemonic leaves to your judgement, and each has appeared as an answer option: your position by latitude and longitude coordinates or range and bearing from a known point; the number of persons aboard and the nature of any injuries; an estimate of the vessel's present seaworthiness; and a description of the vessel giving length, colour, hull type, trim, masts, power and any additional distinguishing features .

Two more points of the placard sequence that MIPDANIO compresses:

• The identity block is the vessel's name spoken three times, then the call sign, then "over".
• You close by stating the channel you will be listening on — "I will be listening on channel 16/2182" — and then end the message with the vessel's name and call sign.

When nobody answers

Release the microphone button briefly and listen for acknowledgment. If no one answers, repeat the proword and the identity block. If there is still no acknowledgment, or if the Coast Guard or another vessel responds, transmit "MAYDAY" or "PAN" with the vessel's name and go on to the position . Where the situation permits, stand by the radio; if there is no answer, repeat, then try another channel.

The standing instruction is to continue to transmit MAYDAY until acknowledged USCG Boatswain Manual Ch. 7 §7.2. The same section sets the order of resort: VHF channel 16 MAYDAY with DSC if the set is equipped, because DSC transmits identity and position automatically; EPIRB activation where a rapid response is critical; visual flares and signal mirror as backup.

Recognising a distress signal when another vessel makes one

The enumerated signals indicate distress and need of assistance when used or exhibited either together or separately . That phrase decides its own question: no signal on the list needs a second signal to accompany it.

The values in the list that separate answer options:

• A high intensity white light flashing at regular intervals from 50 to 70 times per minute.
• A gun or other explosive signal fired at intervals of about a minute.
• Rockets or shells throwing red stars, fired one at a time at short intervals.
• A rocket parachute flare or a hand flare showing a red light; a smoke signal giving off orange-coloured smoke.
• A square flag having above or below it a ball or anything resembling a ball; the International Code Signal N.C.
• Continuous sounding with any fog-signalling apparatus; flames on the vessel; SOS in Morse Code; the spoken word "Mayday".
• Slowly and repeatedly raising and lowering arms outstretched to each side.
• EPIRB signals; a ship-to-shore alert by Inmarsat or other mobile satellite service ship earth station; signals from radiocommunication systems, including survival craft radar transponders meeting 47 CFR 80.1095.

The list is enumerated. An option that does not appear in it is not one of the signals which indicate distress under the rule, which is usually the fastest route to an answer on a four-option recognition question.

You sight a white light flashing at about 60 times per minute. Distress signal or not?

Distress. A high intensity white light flashing at regular intervals from 50 to 70 times per minute is enumerated in . A rate stated well outside that band is not the enumerated signal, and that is how the distractor is usually built.

The paperwork side

Emergency instructions must be posted in conspicuous locations accessible to the crew, with two carve-outs . On a vessel operating with fewer than 4 individuals on board, the instructions may be kept readily available instead of posted. Separately, the rough weather, anchoring, man-overboard and firefighting procedures may be kept readily available as an alternative to posting regardless of crew size. A placard bearing the recommended emergency broadcast instructions satisfies the placard requirement of §184.506 .

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Telling it apart

The criterion is whether the transmission is voice or a DSC data alert, and on which band. Four numbers get swapped for one another on exams because they cluster in pairs.

• VHF channel 16 — 156.8 MHz. Voice, for emergency and calling only. Most often misfiled as the channel a DSC distress alert is sent on.
• VHF channel 70. DSC distress alerts only. Misfiled as a voice working channel, or overlooked entirely by a candidate who assumes all distress traffic is on 16.
• 2182 kHz. Voice on SSB, the MF partner of channel 16. Misfiled as MF DSC.
• 2187.5 kHz. MF DSC distress alert. Misfiled as 2182 kHz by a candidate reading the option too quickly.

The remaining DSC frequencies — 8414.5, 4207.5, 6312, 12577 and 16804.5 kHz — travel as a block with 2187.5 kHz in both 33 CFR §87.01 and COLREGs Rule 38(l). Learn the block as belonging to DSC, and 2182 as belonging to voice.

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Working a question

A 46-foot uninspected passenger vessel with six passengers and one deckhand aboard strikes a submerged object 3.2 miles, 190° true from the sea buoy. She is taking water aft faster than the bilge pump can handle. One passenger has a head laceration. The set is VHF-DSC with an MMSI programmed and a GPS feed.

1. Classify the situation. Progressive flooding with seven persons aboard is immediate danger to life and property, so the proword is MAYDAY, not PAN 46 CFR §184.510. This is the whole decision; everything below is execution.
2. Send the DSC alert first if equipped. It goes out on channel 70 and carries identity and position automatically, which is why it heads the order of resort in USCG Boatswain Manual Ch. 7 §7.2. It does not replace the voice call.
3. Confirm the radiotelephone is on and select 156.8 MHz (channel 16).
4. Transmit the proword three times, slowly, clearly, calmly, then the identity block: vessel's name three times, call sign, "over" .
5. Release the button and listen. No acknowledgment means you repeat steps 4 and 5, not that you abandon the format.
6. Open the message body with "MAYDAY, (vessel's name)", then give position — here range and bearing from a known point, 3.2 miles 190° true from the sea buoy, which the rule accepts in place of latitude and longitude.
7. State the nature of the distress: struck a submerged object, flooding aft, pump not keeping up.
8. Give the number aboard and the injuries: seven persons, one head laceration. Both halves of that step are required content.
9. Estimate present seaworthiness, then describe the vessel — length, colour, hull type, trim, masts, power, distinguishing features.
10. Say which channel you will be listening on, and end with the vessel's name and call sign. Then stand by the radio; if no answer, repeat and try another channel.

If the flooding outruns the pump and a rapid response becomes critical, the EPIRB is next in the order of resort, with flares and signal mirror as backup .

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Where candidates lose the point

Chooses channel 16 as the DSC distress frequency, because everything else about distress lives on 16. The DSC alert is transmitted on VHF channel 70 33 CFR §87.01.

Answers 2182 kHz where the question asks for the MF DSC frequency. 2187.5 kHz is the DSC frequency; 2182 kHz is the voice frequency you select alongside channel 16 46 CFR §184.510.

Downgrades a MAYDAY to PAN because the vessel has not sunk yet. The trigger is immediate danger to life and property — a flooding hull with passengers aboard meets it whether or not the vessel is presently on her way down.

Gives the number of persons aboard and stops. The step also requires the nature of any injuries, and a distractor option that omits injuries is written to catch exactly that reading 46 CFR §28.265.

Rejects a flashing white light as a distress signal on the assumption that white means navigation lighting. At 50 to 70 flashes per minute it is enumerated as a distress signal .

Treats two signals as necessary before distress is indicated. The signals indicate distress used or exhibited either together or separately.

Assumes emergency instructions must always be posted. On a vessel operating with fewer than 4 individuals aboard they may be kept readily available instead .

Stops transmitting after one unanswered MAYDAY. You repeat, try another channel, and continue to transmit until acknowledged USCG Boatswain Manual Ch. 7 §7.2.

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Check yourself

You have a controllable leak twelve miles offshore, the pump is holding, and you want a vessel to stand by in case it worsens. Which proword, and on what frequency?

PAN—PAN—PAN, on 156.8 MHz (channel 16 VHF) or 2182 kHz. There is no immediate danger to life or property at present, which is the condition 46 CFR §184.510 attaches to PAN. If the pump loses the fight and the hull begins to flood, the situation changes and so does the proword.

Your DSC set is programmed with an MMSI and fed by GPS. You press the distress button. On what frequency does the alert go out, and what does it carry?

VHF channel 70 33 CFR §87.01. The alert transmits identity and position automatically, which is why it comes first in the order of resort in USCG Boatswain Manual Ch. 7 §7.2. It does not excuse you from the voice MAYDAY on channel 16.

A vessel two miles off is firing rockets throwing red stars, one at a time at short intervals. She shows nothing else. Are you looking at a distress signal?

Yes. Rockets or shells throwing red stars fired one at a time at short intervals are enumerated, and the signals indicate distress whether used together or separately . No second signal is needed to make the first one count.

You have transmitted MAYDAY three times with your identity on channel 16 and heard nothing back. What do you do next?

Repeat the proword and identity block. If there is still no acknowledgment, continue into the message body, and if the situation permits stand by the radio, repeat, then try another channel . You continue transmitting MAYDAY until acknowledged .

You are running a vessel with a master and one deckhand aboard. Must the emergency instructions be posted in a conspicuous location?

No. Operating with fewer than 4 individuals on board, the instructions may be kept readily available as an alternative to posting 46 CFR §28.265. Readily available is not the same as stowed in a locker under the spare line.

You are into the body of a MAYDAY message and have given position, nature of the distress, persons aboard and injuries. What else must the transmission contain before you sign off?

An estimate of the vessel's present seaworthiness and a description of the vessel — length, colour, hull type, trim, masts, power and any distinguishing features — followed by the channel you will be listening on and a close giving the vessel's name and call sign . These are the items MIPDANIO buries under "Information".

A question offers "a white light flashing at 120 times per minute" as a distress signal. Take it or leave it?

Leave it. The enumerated signal is a high intensity white light flashing at regular intervals from 50 to 70 times per minute . A rate stated outside that band is not the signal the rule describes, and the same trick is used on the gun fired "at intervals of about a minute" by offering shots in rapid succession.