Bushwalkers, PLBs and the RCC

There has been some discussion on one or two of the bushwalking type chat pages about the use of PLBs - often referred to as EPIRBS, the term used for marine beacons - and the likely action, or inaction, that RCC Australia takes.

To set the record straight, all distress alerts received from the Cospas-Sarsat satellite system are treated as one of the 3% real distress situations until proven otherwise.

It is true that approximately 97% of alerts from distress beacons are non-distress alerts but this does not mean that alerts are not followed up. The actions taken depend on the frequency that the alert is received on. If a 406 MHz alert is detected, we know that it is definitely a distress beacon because we receive the unique identifying code that can be decoded to provide ownership information. Once received, contact can be made with the owner or a nominated 24 hour contact to ascertain the situation. Hence, a false alert can usually be sorted out with a phone call and little or no fuss. Importantly, scarce SAR assets need not be deployed for a non-distress situation.

On the other hand, an initial alert received on the 121.5 MHz frequency presents a more complex problem. A 121.5 MHz alert is anonymous and may even be caused by interferers and other extraneous system generated signals. Even if from an analogue beacon operating on 121.5 MHz, we have no way of knowing whose beacon it is or the exact position of the beacon. Once the SAR Officer assesses that the alert may be generated by a distress beacon, he seeks further intelligence. Firstly, Air Traffic Control services are contacted to alert aircraft in the probable areas to listen on 121.5 MHz (the aviation distress frequency) in an attempt to hear the beacon. Often, an aircraft will hear the beacon before a second satellite passes over the area and the position is then resolved. In addition, the other SAR authorities responsible for the areas around the two unresolved positions are contacted to see if there are any operations in progress that might account for a beacon alert. The satellite system will no longer pick up alerts from 121.5 MHz beacons from 1 February 2009. Although aircraft will still be able to detect the beacons, very few listen on the frequency all the time and you would need to be under a major flight route to be detected.

Once the position is resolved assets are dispatched to home on the signal and, hopefully a successful rescue follows.

Australia is one of a small number of countries with the Mission Control Centre for the Cospas-Sarsat system located in the Rescue Coordination Centre and operated by one of the Search and Rescue Officers on watch. These officers are very astute when it comes to discerning between system derived false alerts and alerts derived from a beacon.

Under no circumstances should people believe that no action is taken on an initial distress alert.

The answer is "Switch to 406". The newer technology being introduced means the price is coming down without detriment to accuracy or the other superior characteristics that the 406 MHz beacons have over the 121.5 MHz units.