I'm curious about your comment about 406 MHz ELTs[1].

(I'm not a pilot, though I know a few.)

(First, a clarification, the old 121.5 MHz ELTs also require their manufacturer approved batteries to be replaced every few years in order to maintain their certification.)

(I also don't know the stats on whether ELTs are effective at saving lives or not. I can only assume they are though as anything that can speed the rescue of a lost or injured person greatly increases their chances of survival.)

My direct experience comes from the other side - finding people using ELTs (planes), PLBs (people), and EPIRBs (boats) - with a county Search and Rescue team in California. (To be fair, while we have a lot of rugged backcountry, we don't get a huge number of plane crashes in remote areas.)

I will strongly argue that - aside from price - the new 406 ELTs are far superior.

For those of you who don't know, all ELTs transmit a special signal[2] on 121.5 MHz which can be picked up with radio direction finding equipment[3].

Here's how a search works with the old ELTs - a plane crashes and sets off the beacon. The signal is hopefully heard by another airplane in the area who happens to be monitoring 121.5, by a ground-based monitoring station within range, or by a SARSAT[4][5] satellite when it makes a pass overhead every 90 minutes. Any of those can only detect the presence of a signal and its relative strength. So, now, once the info goes up the chain and back down the chain to the locally responsible agency, a search is initiated. Other info will be used as well - radar tracks disappearing, ADS-B data, etc. - but from the ELT side, teams will head to high points in the area with their RDF equipment and take multiple bearings on the signal which are triangulated to focus the search area. Once they make access to the area, the RDF equipment is used to further refine the location. If available, Civil Air Patrol and other airborne assets are also tasked with locating the plane via ELT signal as well as visually. This is fine and good and all works quite well. It is slow though. It takes time for the signal to be noticed and it takes time for the signal to be triangulated.

The new ELTs also transmit a digital packet on 406 MHz which includes a bunch of data including a serial number and the beacon's coordinates.

So, now searching for a plane with a new ELT now goes like this - a plane crashes and sets off the beacon. It starts sending out a digital burst every 50 seconds or so which is picked up by a satellite or ground-based receiving station. Satellite data goes to the Air Force Rescue Coordination Center[6] which then validates the information and passes it - including the coordinates - to the locally responsible agencies to initiate a rescue. (As an aside, since the signal incudes the serial number which has been registered to the owner, they will know details of the aircraft and can attempt to contact the owner to possibly confirm it was an accidental activation, or gather other information.) Now that the local agencies have the coordinates, they can make direct access to the location and effect a rescue in a much more timely and less resource-intensive way.

In one notable crash - of an experienced bush pilot - I was involved with, it were primarily found when they were reported as late in returning from a flight and the wreckage was identified as the large black spot on the side of a mountain directly inline with their last few ADS-B[7] (and Spidertracks[8]) transmissions. (I don't recall if the ELT signal was used or if the transmitter was destroyed in the fire.)

[1] https://en.wikipedia.org/wiki/Emergency_position-indicating_...

[2] https://en.wikipedia.org/wiki/File:COSPAS-SARSAT_Locator_Bea...

[3] https://en.wikipedia.org/wiki/L-Tronics

[4] https://www.sarsat.noaa.gov

[5] https://en.wikipedia.org/wiki/International_Cospas-Sarsat_Pr...

[6] https://www.1af.acc.af.mil/Units/AFRCC.aspx

[7] https://en.wikipedia.org/wiki/ADS-B

[8] A proprietary aircraft tracking system which sends location and other data via the Iridium satellite network. https://en.wikipedia.org/wiki/Spidertracks