How good would a PLB be in a slot canyon?
If you open the pdf version of Doug's "Second Evaluation of 406 MHz Location Protocol Distress Beacons" (see the link on the main ETS page), then go to page 50, you'll see a section called "Inland Scenario Foxtrot" which is described as:
"developed to assess the ability of the COSPAS-SARSAT system to receive an alert and derive a Doppler location in circumstances where the beacons had a very narrow and limited sky view, as when survivors are located in a narrow canyon."
and
"depth of the gorge where the beacons were placed was approximately 30-40 feet plus trees lining both sides. It was approximately 15-20 feet wide at the bottom and approximately 30-40 feet wide at the top at the point the PLBs were located."
The results:
"All three PLBs were picked up by the GOES 10 satellite, which would provide an "immediate" alert in an actual emergency."
"All three PLBs were picked up by the Low Earth orbiting (LEO) satellites on their first pass, about 25 minutes into the test, which provided a Doppler location." This is the non-GPS locator.
"The McMurdo Fastfind Plus PLB did obtain a GPS fix from the bottom of the gorge". I'm not sure if the otehrs did get a GPS fix or not, but the conculsions point out that such a limited view of the sky could easily have resulted in not getting a GPS fix.
Of course, even without a GPS fix, the Doppler location will still send people looking in the right area. Hopefully you'll have a signal device that can draw their attention when their in your area.
A PLB with a new SiRF III GPS chipset currently used in Garmin's GPSMAP 60 and GPSMAP 76 series would almost certainly have gotten a GPS fix under these conditions. The abilities of these GPS's to get a fix under nasty conditions is nothing short of amazing.