The international group that monitors ELT's manadated stopped monitoring 121.5 over ayear ago and moved monitoring to 406. They announced this change quite a few years ago to give the World time to switch over to the new frequency. The World switched over pretty much all except the FAA that is which still hasn't gotten around to mandating a switch over dispite requests from the NTSB and others.
The 121.5 frequency is very cluttered with sources of interferance ranging from pizza overs to malfunctioning TV sets. It also produces a signal that is not very precise and cannot be easily homed in upon. I successfully hunted down dozens of 121.5 units in my CAP days and I can tell you the signal was so imprecise that it was vitually impossible to locate one of the units without air support, which of course you would not have in bad weather when most aircraft go down. (Even with air support we often couldn't pin point 121.5 signals especially in mountainous terain because the 121.5 signal bounvces so much.) A 406 unit I hunted down by contrast let me drive over to the person's driveway where his boat's EPIRB was going off (the Coast Gaurd has manadated a 406 switchover) without any need for air support.
The new 406 units send up a databurst on the 406 frequency that includes the unit's registration # which is tied into a database with the owners phone numbers, home base, and address. Some 406 units have a GPS built in and also send the units lat/lon up to the satelite on the databurst. Geosychronus stalites will immediately pick up this signal and a search will be immediately initiated. With the old system, 2 to 3 passes of orbitting satelites were required before a search could begin which would take 6-12 hours (significantly lowing crash survivability). I had my new 406 ELT go off (my oil pressure gagaue sprang a leak and shorted out my remote switch) and was notified by phone within a half hour of the problem by the Air Force.
One poster incorrectly stated the 121.5 is still being monitored in the US. I think he is confused about the 121.5 secondary signal on these units. The 406 signal is a databurst, making it hard to home in on so these units also transmit a low power 121.5 signal that can be homed in on by standard direction finding equipment used by ground personel. 121.5 in NOT monitored by the satelite system any more.
A lot of people are buying 406 EPIRB's instead of ELTs. I went with the ELT because it has an easy to reach switch a can flip as I am going down and an auto activate feature if I should crash and be unconcious without having flipped the switch first. Mine is an Artex. The unit works great although Atex customer support leaves something to be desired.
Bottom line, your 121.5 unit is good to meet the FAAs rules, good if someone knows when you have crashed, knows approximately where you have crashed, and is able to send an airplane to that location to look for you. (If they know and can do all of that, do you really even need an ELT?) It can also be used for such purposes as a paperweight and door stop.
A 406 unit by contrast can be used to let people who don't know when and where you have crashed be able to find you.
Helen
May 17, 2010 05:09:25 PM, Sport_Aircraft@yahoogroups.com wrote:
May 17, 2010 05:09:25 PM, Sport_Aircraft@yahoogroups.com wrote:
Can anybody share their knowledge about these new (to me) doo-dads? I just read that nobody will be listening to my old 121.5 Mhz ELT if it goes off anymore. Is it mandatory that it be upgraded? Do the smaller (cheaper) 406 MHZ PLB's suffice? Can anybody suggest a decent one? Thanks in advance for the info.
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