Commandant (G-TTM)
U.S. Coast Guard                   29 September 1995
Washington DC 20593


An EPIRB Story

This narrative describes the difference in detection between a
121.5 MHZ emergency position-indicating radiobeacon (EPIRB) and a
406 MHZ EPIRB.

The Thirteenth Coast Guard District (D13) rescue coordination
center in Seattle WA prosecuted three 406 MHZ beacon cases in a
recent 4-5 day period.  The  incidents occurred in the 300-800 NM
offshore range.  Two were actual  distress with good saves, one
was a false alarm (beacon swept overboard in  heavy weather). 
None of the beacons were recovered.

The beacons continued to perform impressively (in terms of
endurance, anyway)  producing hundreds of 406 and 121.5 alerts. 
The 406 alerts were no problem,  but the clouds of 121.5 alert
"chaff" were something else.   

Over the course of the week they handled on the order of 1500
121.5 alerts.   This extraordinary alert volume would have
discouraged many from the careful  scrutiny required to discern
possible independent 121.5 distress alerts from  the "sea" of
homing signal generated alerts.  The volume could have easily 
task saturated/overwhelmed others, however dedicated.

D13 created a spread sheet and used GDOC (Geographical Display
Operations Computer) to collect and evaluate the alert  data, and
then dispatched aircraft to investigate 121.5 alert "hot spots"
that  seemed inconsistent with the apparent patterns of known 406
beacon signal  generated alerts.

Their diligence and vigilance paid off when CG 1703 (SACTO)
located a raft  with two survivors 650 NM offshore at the hottest
"hot spot".  The father and  son pair's sailing vessel had gone
down in violent weather about four days before.   D13  diverted a
cargo vessel for the pickup.  

The pair's 121.5 beacon appears to have functioned normally for
the duration  and was still transmitting as the aircraft arrived
on scene, but the  anonymous 121.5 distress signal difficult to
recognize amidst the sea of  homing signal alerts.