This marine notice supersedes Marine Notice 10/2017.
Users should be aware of the implications of the automatic channel switching feature in VHF DSC radios being enabled during safety critical operations. Instructions on its use should be included in the ship’s bridge procedures.
Management of the automatic channel switching feature
VHF marine radios with DSC capability have a function that enables automatic channel switching to VHF channel 16, when a DSC distress alert is received.
This design function complies with the International Telecommunications Union (ITU) Recommendation ITU-R M.493-15 (2019).
Users should be aware that the automatic channel switching function can be disabled to prevent automatic channel switching.
If automatic channel switching is disabled, transceivers will continue to detect DSC distress alerts. The user can then decide whether to accept the channel switch request.
Manufacturers implement the feature in different ways and usually include instructions in the user manual.
Equipment should provide a visual indication when the automatic switching function is disabled. If the user manual or documentation is not clear in this regard, advice from the supplier or service agent should be sought.
Ships’ bridge procedures should include instructions on how and when to disable and re-enable automatic channel switching during safety critical operations.