WHY 406MHz IS NO GOOD FOR MOB SAFETY COVER?
406MHz PLBs are not water activated i.e. not auto-activate and operate through a satellite system. A man overboard situation demands a solution which provides immediate and automatic alerting that a person has gone into the water and immediate tracking of that person, ideally, by the people still onboard the vessel. A 121.5MHz PLB is a fully automatic/water activated unit which will immediately raise the alarm when a person falls overboard and allow that person to be quickly tracked an recovered by the people still on the vessel. 121.5MHz is also the International Search and Rescue homing frequency and can be tracked precisely by both onboard locating units such as the Sea Marshall® SARfinder® and by the Coastguard. Not many people realise that 406MHz plbs have to rely on a very low power 121.5MHz homing transmitter built into the unit to be able to be tracked, the 406MHz element can only give a satellite fix to within 6km square. A lot of people are buying 406MHz plbs in the belief they are good for man overboard safety cover…they are wrong. Here's a comparisson of what happens in a man overboard situation between the two types of plb:

Here's what happens when a 121.5MHz high power plb is used in a Man Overboard incident….
  1. Person falls overboard into cold water …and is possibly knocked unconscious or goes into cold shock response.
  2. After 5 seconds the PLB self activates providing a high power 121.5MHz homing signal to track to.
  3. Vessel turns toward 'SOS' target and person is recovered, all this can have taken place in less than 5 minutes!
  4. Worst case scenario the MOB cannot be recovered by the boat, the Coastguard are called and told there is an MOB at these co-ordinates wearing a high power 121.5MHz plb. A Coast guard helicopter is deployed, they can track this 121.5Mhz signal from up to 30 miles away.
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Here's what happens when a 406Mhz is used for Man Overboard…
  1. Person falls overboard into cold water …and is possibly knocked unconscious or goes into cold shock response.
  2. The person in the water has to take out their beacon, extend the antenna and switch the unit on whilst holding it upright…not easy if your unconscious, or you can’t swim, or you go into cold shock response and you simply can't move.
  3. The person in the water now has to hold the plb upright whilst bouncing around in the ocean, they have to keep the unit upright unitl a satellite fix occurs…this can take up to 90 minutes.
  4. If a satellite fix is acquired the SAR authorities on the ground will then check whether the beacon is registered or not (406MHz plbs have to be registered to a specific person and cannot be swapped between crew) at this point they will initiate a Search And Rescue. The important thing to note is that more than an hour could have lapsed by the time this happens.
  5. Once the SAR crews get within range of the incident they have to switch to 121.5MHz to actually home into the beacon!
...you get the idea

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