Flaws in the system - Part 2

The false alert problem

The DSC mess

The GMDSS DSC system, particularly on HF, is plagued by an appallingly high false alert rate - in excess of 99.5%.

This situation has reached critical levels, to the point that there is talk of discontinuing DSC...

The root of the problem is that there is no real central operational and administrative authority to oversee the DSC system - the operation of DSC systems on vessels is effectively managed/regulated by individual Flag States.

The Inmarsat system used to suffer from a false alert rate approaching that of DSC - Inmarsat instituted a strong and well managed program to combat the problem, with the result that the Inmarsat false alert rate has dropped to negligible levels.

The situation has reached the point that DSC has become an impediment to safety at sea.

Equipment complexity

Much of the DSC equipment available today is far too complex to operate.

In addition, the operating routines vary significantly from brand to brand, such that a user trained on one type of equipment will have considerable difficulty operating another.

DSC controller operation is complicated by the inclusion of many (unnecessary) commercial functions - DSC controllers can be used to make automatic telephone calls via suitably equipped HF Coast Stations.  Unfortunately, there are very few, if any, Coast Stations that offer this service.

Many controllers are equipped with small display screens - this makes operation very difficult. There was a move some time ago at IMO* to mandate a minimum DSC display screen size of 4 lines by 64 characters per line.

This recommendation was modified to require that a minimum of 160 characters be displayed in two or more lines. These modifications have taken effect for all new equipment fitted to ships as from 1 January 2000.

There is nothing in the IMO performance standards to prevent manufacturers using a Personal Computer type system for DSC, i.e.: one with a large display screeen - however none have been produced, probably because of cost.

The modifications also mandated connection of a GPS and also the provision of an alarm to indicate that no position data is received from the GPS or, in the case of manual input, the position information is over 4 hours old.  Any position information not updated for more than 23½ hours is also required to be erased from the system.

Some manufacturers are producing simple to use DSC systems, with large display screens.

It is hoped that this trend will spread.

*instigated by the author

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A new DSC standard is here

After seven years of effort, ITU and IEC have at long last finished the final standards defining a simplified DSC radio, with a standardized software interface, free of most of the unnecessary alarms and strange operation that has plagued the system since its inception.

The new standard is designed to radically simplify the man-machine interface, and automate most functions.

A draft copy of the new requirements showing the revisions may be viewed here. 

The standard has since been amended again - revision 13 (the latest) may be found here

False alerts

Equipment complexity is leading to an unprecedented number of false alerts being transmitted.

The majority of these are caused by human error, however some have been known to be deliberately sent out of ignorance by system installers - they program in a bogus MMSI, and just push the distress button to see if the system works....!

Such alerts are relatively easy to spot - the position is often suspect (12.34s 123.45e, for example), and the MMSI is often equally dubious (123456789, 111111111, 222222222, etc).

Can the system be too effective ?

HF DSC's effectiveness and world-wide range is leading to its downfall.

Alerts are often received from stations quite literally on the other side of the world. It is not uncommon to receive a 12 MHz DSC alert from the North Sea in the South Pacific....

Whilst this is quite interesting from a technical perspective, it is a complete waste of time from a SAR viewpoint.

Compare the DSC system with Inmarsat - with Inmarsat, alerts are directed straight to the RCC - surrounding ships are only alerted via a carefully controlled re-broadcast from the RCC.

Although HF DSC is designed for ship-shore alerting, it operates in a broadcast mode - all ships monitoring the frequency receive the call, and all are therefore able to relay it......

Users are too enthusiastic...

The ITU operational guidelines for HF DSC require that, basically, a vessel receiving a HF DSC alert is to immediately set watch on the corresponding R/T or NBDP channel for the band in which the DSC alert was received and await communications from the vessel in distress.

However, this is not happening - vessels are relaying HF DSC alerts indiscriminately.

Ironically, the original distress alert being relayed is, in itself, probably false...

This is leading to serious congestion of the DSC channels - to the point that the original alert has become so corrupted that it appears a Coast Station is in distress !!

Unfortunately, DSC is becoming an end in itself, rather than a simple alerting mechanism.

Many ships fail to adequately consider the information in a received alert before relaying - an alert from a ship with an obviously false MMSI (such as 123456789) should not be relayed.

Perusal of the international MID list reveals that the following MID numbers are not allocated:

000 123 222 333 444 777 888 999

It is very difficult for a ship's operator to change his/her DSC system's MMSI at sea, so one can safety assume that MMSI's with the above MID's must be bogus.

Users receiving a DSC distress alert from a vessel with a MMSI starting with any of these MID's can therefore IGNORE the alert - it can not be genuine.