Hi Chris,

The Emergency Locating Transmiter (ELT) used by most general aviation aircraft operates on 121.5 mHz. This frequency is monitored by satellites orbiting the earth. Part of the delay in reporting of the ELT's is due to the fact that the first pass of a satellite over an activated ELT signal does not immediately initiate search & rescue, the first signal received needs to be confirmed by a second satellite pass. This may take several hours. As mentioned above, 121.5 mHz is line of sight transmission. In mountainous terrain, if an ELT is activated in a valley or gorge, the usable signal available to search & rescue is grossly diminshed.

There are other factors that come into play as well. Most ELT activations are accidental, so there can be a bit of field work involved at the local airports where many ELT's have been set off by wind blowing on the tied down aircraft, various failures of the actual ELT equipment itself, inadvertant pilot/passenger activations (hey, lookit this little silver switch, wonder what it does, click, hmmmm...nothing obvious happened), then it's forgotten until some hot / tired / cold / wet and in most cases, severely irritated (rightfully so, IMO) CAP and/or other S&R personnel using direction finding equipment, finally locate the ELT in question, which is all too often in an airplane tied down with unreachable owners/operators. All this can lead to the "cry wolf too often" issue.

In many cases, other aircraft flying overhead may hear the ELT and report it to Air Traffic Control. When able, many pilots will take to time to circle the area and try to define where it may be originating, and report that to ATC as well. Sadly, there are other instances where fuel does not allow the luxury of time to spend looking in depth as many of these other aircraft are typically are well into their flight.

I've required my student pilots to monitor 121.5 at all times when safely feasible, and have on ocassion, reported activated ELT's to ATC. As far as I know, they were all false alerts, but it only takes one real one to save a life.

Another good thing for pilots to do, is just after shutting down the aircraft, turn on the radio for a moment and check to see if an ELT is going off. Too often, this simple item is overlooked in the rush to leave the airport...

There are more aspects to your original question, but this should cover most of the primary points of the equation. There are a number of S&R folks on these forums that may also jump in with other items of interest.

edit: ELT's have also been known to fail to operate (with disasterous consequences) as well. See the tale of two crashes elsewhere on this site.

Regards,
Comanche7