I wrote to the USCG asking whether there was in fact a delay between when an EPIRB signal is received and help is dispatched. The USCG says NO DELAY. Here's the letter:
PLB's are an excellent way to alert Search and Rescue (SAR) authorities of an emergency. Just as with VHF radios, the Coast Guard does receive a number of false alerts from these devices, but there is not a deliberate time delay from the Coast Guard when there is a known emergency. The system does have its limitations which can delay the emergency message from being forward to the Coast Guard, but understanding the system can eliminate much of that delay.
The 406 Satellite Emergency system uses two different satellite systems to "listen" for distress beacons.
-One Satellite system is the Low Earth Orbiting Satellite (LEO) which obits around the poles. This system uses Doppler to locate a beacon that has been activated. It can take up to 90 minutes for the satellite to pass over a beacon, and it usually requires two passes of the satellite for it to determine a position.
-The other Satellite system is a Geostationary system. The satellites in this system "hover" over a spot on the earth and can see approx 1/3 of the earth at a time. The GEO satellites are not able to use Doppler location processing since they have no relative motion between them and the emergency beacons. Therefore, they are not able to determine a location for a beacon. They can, however, provide immediate alerts. This is a valuable tool for SAR personnel since it allows them to begin their initial verification of the alert using the National 406 MHz Beacon Registration Database. Often this detective work yields a general location of the vessel or aircraft in distress and SAR assets can be readied or dispatched to that general area. Ideally, a LEO satellite will fly over the beacon within the next hour and calculate a Doppler location which will be given to the SAR personnel who may already be enroute.
How can you decrease the time for alerting SAR authorities you are in distress? Ensure your beacon is equipped with GPS. GPS equipped emergency beacons send the GPS position along with the distress alert when it is activated. The GEO satellites would receive the alert along with the position provided by the GPS in the beacon. The second thing that can be done to quicken the response time of SAR authorities is to properly register and keep up to date the registration for your beacon.
Two important considerations: First, a GPS-equipped beacon only works when the receiver has a clear view of the sky in order to permit the receiver to self-locate. Often times, conditions do not permit this which may either distort the positional accuracy or negate it altogether. Because of this, the 406 emergency System relies upon the Doppler locating effect as the primary means for locating a beacon. This process is able to overcome the limitations of a GPS unit and still generate a fairly accurate location...within a mile for positional accuracy. Secondly, the GEOSAR component only works if the beacon is registered with NOAA. Without registration, the RCCs are unable to react as quickly...and ultimately this may delay a SAR response should you be in an emergency. Keeping the beacon properly registered with NOAA at the National 406 MHz Registration Database can save valuable time during an actual emergency. There is even a comment section on the beacon registration site that allows you to put info such as, where you will be sailing, time you expect to be out, number of people on board, etc. This information is forwarded to SAR authorities when the beacon is activated.
