All ELTs have one thing in common, their main purpose is to notify potential rescuers (by different means) that an aircraft has run into a solid object and someone could be in need of help. But the technology for doing this is in the midst of a big change.
Most current ELTs operate at 121.50 and 243.00 Mhz. This signal can be traced by some satellites, Civil Air Patrol, and picked up by the military on the 243.00 MHz frequency. But these frequencies are too low for pinpoint location by satellite. The satellites' accuracy is normally around 20 kilometers at best, and that's quite a radius to search especially if the fallen aircraft is covered by trees. The Civil Air Patrol says it can often take 1015 hours to locate a downed aircraft once the satellite tells them where to look.
I'd hate to be pinned upside down in a Beech, Cessna or Piper for that long. Of course it could be worse, like being upside down in a Grumman Tiger or a Lancair...
The new 406 MHz ELT frequency is optimized for accurate satellite location. It provides a far better signal-to-noise ratio, and the satellites love a clear signal to listen to. The new satellites that listen to 406 Mhz also have the capability of looking at a lot more data and locating signals with far greater accuracy.
Each new 406 Mhz ELT has a discrete digital code that it transmits up to the satellite. The satellite transmits this information back down to the ground. The ground station reads this code and determines who owns the aircraft and what its tail number is. (When you purchase a 406 Mhz ELT, there is a card you fill out and mail in that puts you in the database.) I think you can already see how handy this information could be to ground personnel.
Satellites can locate a 406 MHz ELT within about two kilometers. That's ten times more precise than with 121.50/243.00 signals, and can cut down the search area by a factor of 100. I'm told that the average time to find an aircraft with a 406 Mhz ELT is around 4 hours, versus 10 to 15 hours with the old system. Those precious hours could be very important if you were hurt or in the vicinity of hungry bears.
From what I hear from the manufacturers, they have never experienced a false alarm with one of the new ELTs. This is probably because of the high-tech "G" switches the new TSO C126 ELTs now have.
It might be a bit early to get rid of your old 121.50/243.00 MHz ELT, because not all ground and air rescue units are yet equipped with direction finding gear to home in on the new 406 MHz signals. This leaves a couple of options.
You could add a new 406 MHz ELT beside your existing 121.50/243.00 MHz ELT to provide the best of both worlds. This would require adding a second ELT antenna or purchasing a dual ELT antenna. You can also purchase a new combination unit that transmits on all three frequencies.
But you might also want to wait a few more months before doing anything. Plans are in the works for enhanced 406 MHz ELTs that are hooked to your GPS receiver and will transmit your last known latitude and longitude along with the normal digital aircraft signature that all 406 Mhz ELTs transmit. I'm told that the ELT manufacturers expect this new capability to be available in the third quarter of 1997.
The new top-of-the-line ELTs may cost close to $3,000, but will transmit the owner's name, tail number and last known position. With this data rescue could be less than an hour! This series of ELTs is aimed for the corporate market but I personally think my life is just as valuable as any corporate officer. You may want to give it some thought if you are in the market for a new ELT.
I'd strongly recommend discussing the installation and details with your avionics shop. Things are changing rapidly on the ELT front, and the manufacturers I called and questioned about the 406 Mhz ELTs were meaner than junk yard dogs. Avionics shops are usually a little kinder.