Module 8 - Digital Selective Calling
False DSC Distress Alert
What you will learn
Cancel an inadvertent VHF DSC distress alert using the current ordered recovery sequence and a complete Channel 16 broadcast.
Silence does not cancel a false alert. Reset the set, use its cancellation function if available, move to Channel 16 and tell all stations exactly which identity sent the alert in error.
ITU Resolution 349 (Rev.WRC-23) gives the VHF DSC cancellation sequence. Reset the equipment immediately. If the set supports cancellation, cancel the alert using the equipment procedure. Then set Channel 16 and transmit an All Stations broadcast giving vessel name, call sign and MMSI and cancelling the false distress alert.
Do not transmit another distress alert, switch the radio off and hope, or omit the identity through embarrassment. Receiving stations need to connect the voice cancellation to the digital alert they saw. Continue listening and comply with rescue-coordination or coast-station instructions; record and report the incident as required by the operator's procedures.
Prevention still matters: keep the protected control guarded, brief crew, confirm position and nature of distress before a composed alert, and use approved training or test facilities. But once an alert has gone, recovery takes priority over blame.
| Order | Action | Purpose |
|---|---|---|
| 1 | Reset the equipment immediately | Stop repeat alert behaviour |
| 2 | Use set cancellation if available | Cancel digitally where supported |
| 3 | Set Channel 16 | Reach vessels and coast stations by voice |
| 4 | Broadcast All Stations with name, call sign, MMSI and cancellation | Tie the correction to the false alert |
Recover visibly and completely
A crew member accidentally holds the protected control until the set confirms that a VHF DSC distress alert has been sent.
1. Reset and cancel
Reset immediately and use the equipment cancellation function when the set provides one.
2. Broadcast on Channel 16
Address All Stations, give vessel name, call sign and MMSI, and clearly cancel the false distress alert.
3. Stay available
Listen for the Coastguard or other coordination and follow the instructions received.
Sense check: The cancellation is incomplete if a receiving station cannot match the voice broadcast to the original digital identity.
Common mistake or limitation
- Switching off without a Channel 16 cancellation broadcast.
- Sending a second distress alert as a supposed cancellation.
- Saying only 'false alarm' without vessel name, call sign and MMSI.
Recap
- Reset, cancel digitally if supported, then use Channel 16.
- Give vessel name, call sign and MMSI and cancel the false distress alert.
- Listen and follow coordination instructions after the broadcast.
Optional quick check
Section 6 of 9
Which action completes the VHF DSC false-alert recovery after reset and any set cancellation?
Sources and factual review
Reviewed 20 August 2026 - Compass Revision editorial review.
Continue studying Digital Selective Calling
This public lesson is part of Revision Module 8. Full revision access adds the guided Learn, Practise and Test flow, flashcards and revision progress.