Thread: A bit about PLBs

Just thought this was worth sharing

In the event of a beacon being activated a 406MHz distress signal is
relayed almost immediately to the Rescue Co-ordination Centre (RCC)
in Wellington, via a high orbit geostationary SAR satellite. In the following
period of time (the length of which depends on where satellites are in the
sky at the time) low orbit satellites then indicate which part of the globe
the signal has come from. For those users who spent the extra money to
buy a GPS enabled PLB, their location will be narrowed even further by
the transmission of their co-ordinates with the distress signal. Standard
procedure at this point is for the RCC to deploy a helicopter that can get
to the vicinity of the distress signal quickly and then zero in on its exact
location, using on board equipment that can home on the local 121.5MHz
signal that PLBs also transmit.
But what happens if the helicopter can’t get there? Flying in the New
Zealand mountains is governed by VFR (Visual Flight Rules) which
basically say that pilots must be able to see the ground, any obstructions
and other aircraft when flying. Helicopters are not permitted to fly into
clouds—particularly when in proximity to the ground. With our mountain
weather being what it is, we have had, and can expect to continue to
have, instances where helicopters cannot get close to an activated PLB
(or ELT—the aviation equivalent).
For a non-GPS enabled PLB, satellites will only be able to indicate
a location with a 5 kilometre degree of accuracy—in a large tract of
backcountry this may only limit the possible location to an area of
approximately 8,000 hectares! Even for GPS encoded signals, normal
120 metre accuracy will leave a search area of up to 5 hectares (or more if
steep terrain or other obstructions reduce the quality of the GPS fix).