U.S. Federal Aviation Regulation Part 91, paragraph 207 (my squadron number...) details the use of emergency locator transmitters in U.S.-registered civil aircraft. These transmitters (ELTs for short) activate whenever the unit is subjected to impact, so that in a crash, the radio will automatically alert search-and-rescue personnel.
That's our specialty in the Civil Air Patrol; we find ELTs, either from the air or the ground. We have direction-finding equipment to allow us to quickly track down the source of an emergency signal. It's most often a unit that goes off in error, but we treat every call like there could be lives at risk.
It was a false alarm tonight; I just got back. A corporate jet at the local airport was pinging, so its ELT probably got set off by a hard landing or by being jarred by the tug. We didn't have to launch our plane to find it, I tracked it down with a handheld unit.
(Click here to hear what an ELT signal sounds like. Sometimes I get to listen to that for hours...)
We roused the poor pilot from his hotel, and met him at the plane to turn the beacon off. At least he can sleep in, his morning flight will be cancelled due to the plane being out of service. (That beacon must be replaced now, before the plane can be used for air carrier operations.) It was a beautiful 8-seat jet - the pilot and I got to climb all over it trying to find the transmitter.
Anyway, it was good practice. And I got to play with my new cell phone, which I just bought tonight - a Nokia 6800, that folds out into a little keyboard. It's got Internet access and text messaging, which I'll figure out tomorrow.