Craig Jungers wrote A helicopter, with its ability to fly slowly, probably could home in on a beacon transmitting on 121.5. Joq probably has a better insight to this. Nope -- your insight is right on the money, Craig. It's possible for a SAR helo -- or a fixed wing rescue aircraft -- to fly its "number one" needle in automatic direction finding (ADF) mode to the signal source and mark "on top" when the needle swings erratically and eventually points to the reciprocal heading. The signal should be somewhere close to that point. "Close" is the operative word, here. There's a fairly substantial cone of ambiguity above a signal like an EPIRB (emergency position-indicating radio beacon). But, for practical purposes, that kind of approach to SAR has been supplanted by the international COSPAS-SARSAT system (Search and Rescue Satellite-Aided Tracking in France, Canada and the U.S., with COSPAS being the equivalent acronym in Russian) where an EPIRB transmits a coded, digital 406 MHz signal when a vessel is in distress; this signal is received by a set of geostationary and polar-orbital satellites which work together to specifically identify and localize the activated EPIRB. The satellites, in conjunction with a ground station, create a GPS address for the signal, and send messages to SAR centers which then task an operations center that, in turn, launches a ready aircraft. Depending on the distances involved, this may be a fixed wing aircraft or a helicopter -- frequently both. Essentially, that's all a SAR bird gets these days -- a fly-to point at a specific GPS address; some launches result from radio calls or from reports from shore observers, but that's a visual solution for the pilots. (Note: some 406 MHz beacons also report their GPS location, enhancing and accelerating a SAR solution.) The older 121.5 MHz beacons are no longer monitored by COSPAS-SARSAT, although a rescue aircraft can still home in on a broadcasting 121.5 (or 243) MHz EPIRB. The information provided either by a COSPAS-SARSAT solution or an observation or distress call gets you close to the survivor. Or right on top of a survivor. But that last bit can be the hardest. Seeing a person -- even a kayak hull -- in all that confusing background is hard. For that, many -- maybe most -- Navy, Air Force and Coast Guard SAR flight crews launching at night use night vision goggle (NVG) equipment to see the thermal contrasts created by a person in cooler water. But that's another story. Joq *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************Received on Thu Jul 08 2010 - 17:20:11 PDT
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