Two MF DSC Distress Alerts, No Voice Contact, Marginal Coast Guard Coverage
You are the only licensed operator on watch at a remotely sited public coast station on the Maine coast; the time is 0342 local. The MF DSC receiver monitoring 2187.5 kHz prints a distress alert: format distress, MMSI 316009887, position 44°11.6'N 068°40.2'W, nature 'fire/explosion', time 0340, telecommand 'no information'. Nothing follows on 2182 kHz. At 0349 a second alert from the same MMSI arrives, now with position 44°08.9'N 068°33.5'W. You keep watch on 2182 kHz and hear only atmospheric noise; the VHF channel 16 watch is quiet. The nearest Coast Guard station is 45 nautical miles away and its published MF coverage of your area is marginal. Your station has a 150 W MF transmitter, a working 2187.5 kHz DSC transmitter, and a direct telephone line to the Coast Guard sector duty officer. Three routine radiotelephone calls are holding on your working channel, one of them a fish buyer who has already waited eight minutes.
1. Should you acknowledge this distress alert, and if so, exactly how? Give your reasoning, not just the procedure.
Read the worked answer
Yes - acknowledge, and do not wait for a third alert. An unacknowledged distress alert is an alert that no one has visibly taken responsibility for, and the silence on 2182 kHz is consistent with a vessel whose transmitter (or antenna, or power) has failed while the DSC controller kept working.
Sequence:
- DSC acknowledgement on 2187.5 kHz, addressed to MMSI 316009887, distress acknowledgement, no telecommand.
- Radiotelephone call on 2182 kHz: 'MAYDAY, 316009887, 316009887, this is [station], received your distress alert on 2187.5, over.' Short, twice if there is no reply.
- If there is still no reply, transmit a MAYDAY RELAY on 2182 kHz to all stations, carrying the MMSI, the position and the nature of distress. Ships that copied the DSC alert are listening for a shore station to take charge; the relay tells them the alert has been heard and is being handled, which is what stops a dozen ships all trying to acknowledge at once.
- In parallel, telephone the Coast Guard duty officer on the dedicated line. Do not make the handover conditional on establishing voice contact - the vessel may never answer.
Reasoning throughout: the vessel may be unable to transmit voice but able to press a distress button, so DSC is the only channel open to it.
2. The second alert places the vessel about 5.5 nautical miles from the first, nine minutes later. What does that tell you, and what do you do with the discrepancy?
Read the worked answer
Work the geometry first. The positions differ by 2.7 minutes of latitude (2.7 nm) and 6.7 minutes of longitude, which at 44° latitude is 6.7 × cos 44° ≈ 4.8 nm. The straight-line separation is √(2.7² + 4.8²) ≈ 5.5 nm. Covering 5.5 nm in 9 minutes requires about 37 knots.
A vessel disabled by fire and unable to answer on 2182 kHz does not move at 37 knots. Possible explanations: a manually entered or stale position in the first alert; a second alerting device (a handheld DSC controller, a second console, or an EPIRB) with its own GPS; a position from a liferaft or a grab bag; or a misconfigured or false alert.
Your job is not to adjudicate that. Your job is to make sure the people who can adjudicate have the facts:
- Relay both positions and both times.
- Tell the Coast Guard duty officer explicitly that the two alerts disagree by 5.5 nm in 9 minutes and that the vessel cannot be raised on 2182 kHz, so the RCC can compare against registration data and any other alerts.
- Never conclude on your own that an alert is false, and never cancel one. Only the originating station, or an authority acting under the correct procedure, terminates distress traffic.
- Keep both alerts open until someone with authority closes them.
3. What goes in the log, who must be told, and what happens to the three routine calls waiting on your working channel?
Read the worked answer
Log, in time order and to the minute: each DSC alert (frequency, MMSI, position, nature, time of receipt), your DSC acknowledgement, every 2182 kHz transmission with its content, the negative voice results, and the exact time you reached the Coast Guard duty officer and the time that conversation ended. The log is the only contemporaneous record of how long the alert stood unacknowledged and what you did about it; if the case is later disputed or investigated, that record is what you will be asked for.
Notification: a public coast station that receives a distress alert passes it to the rescue coordination centre. The telephone call is not optional paperwork - it is the handover of responsibility. Until the RCC confirms it has the case, you keep the 2182 kHz watch and stand ready to relay further traffic.
The routine calls stay queued. Distress traffic has absolute priority over all other communications, including public correspondence. Waiting callers are told nothing more than that the channel is handling an emergency, and no details of the casualty are passed. Distress traffic itself is never charged; normal service and normal tariffs resume once the case is closed.