When Doug Ritter (he IS equipped.org) was conducting the 2000 liferaft
testing for Belvoir Pubs, one of the many in-the-water testers that joined us was a LCDR in the USCG who coordinated their 406 Epirb testing program. (The USA's coast guard has a very active testing program directed at commercial
vessels, especially fishing
boats. If you have a 406 and are in the USA, contact your district office and ask about having your 406 tested; they are usually glad to do it, op skeds allowing). This fellow was really knowledgeable about the whole sat/rescue center/rescue responder system works in practice.
Several of us at the testing event were yachties about to go blue water
(that's why we were there testing liferafts) and we asked him about choosing between a GPS-capable 406 and one that wasn't; we all expected to hear the GPS-equipped version be recommended without hesitation, but that wasn't how he responded. Instead, he talked about how the Rescue
Center works a response, about the reliability
of the units over a period of some hours or even days, and the decision tree they work off when they lose a unit's signal. The bottom line was that, if you could be assured your unit would work from when it was triggered until you were picked up, a GPS-enabled unit might be preferable. But if at some point you lose the unit (battery dies, unit sinks, unit fails for another reason, etc.) they would likely work to that position as the proceeded with the rescue
. OTOH if the unit is not sending a position but only a signal - and the unit dies - they would be more inclined to do a standard 'rate of drift and direction' computation (IOW engage their brains rather than believe a 'last reported position'). I'm not fully representing the view expressed and he wasn't arguing against GPS-enabled 406's, but he was breathing a little real-world reality into how rescues work and made us all realize there are two choices there, not just a 'good' one and a 'not good' one.