"Gezellig" wrote in message
...
On Fri, 10 Jul 2009 15:44:52 +0000 (UTC), John Clear wrote:

In article ,
Gezellig wrote:
On Thu, 09 Jul 2009 17:44:28 -0500, Jim Logajan wrote:

http://www.ntsb.gov/ntsb/brief.asp?e...07X17184&key=1

How long after first impact should it take for the ELT to kick out a
call on frequency?

If the ELT isn't destroyed in the crash, it usually doesn't go off until
the wreckage is hauled away.

406 ELTs are slightly better then 121.5 ELTs in terms of false
positives (ELT goes off with no crash), but in real crashes, they
both have extremely high failure rates.

Tell me about it. Mine went off on a maintenance tow

I don't have access to the stats any more, but when I was in CAP,
something like 98% of ELT searches where false activations, and
ELTs failed to activate in about 95% of all crashes. Numbers are
from memory, so might be off by a bit, but the magnitude of the issue
should be obvious.

Holy s**t, I never knew, now I feel better.

Being on flight following and/or getting off a Mayday before crashing
greatly increase your chances of being found. Manually triggering
your ELT before impact might help, if it survives the impact.

John

Thx.

This seems to really involve more than one subject:

1) In the particular case of Steve Fossett; it appears that timely
location would have made no difference at all for Mr Fossett, but admittedly
would have saved a tremendous amount of effort and also expedited and
simplified the settlement of his estate. (As a side note, simply as
serendipity, the search for Mr Fossett did appear to uncover the answers to
some other misteries which had been under investigation for some time.)

2) One of the major arguments for the adoption of the 406Mhz system was
the ever expanding use of the 121.5Mhz beacons by hikers, boaters, and
probably others as well. IIRC, the new beacons were supposed to be
available for the various uses so that searchers would have greater reason
to presume which type of incident might be involved. (I have not ket up,
and don't know whether the change has helped; but there do seem to be some
similarities to the use of other emergency response systems.)

3) When I was working on avionics, it seemed to me that about three
fourths of all radio problems that I saw were airframe wiring as opposed to
inside the radios. The radios themselves have probably gotten more reliable
in the years since, so I would be amazed if the change to 406Mhz has made
much more difference in physical reliability than would have been the case
if all of the old 121.5Mhz beacons were completely removed and then
completely reinstalled during the same time period.

4) In the event that most false or inadvertant activations actually occur
on airports, which would certainly make sense, then there should be a fairly
simple and cost effective method to observe, locate and deactivate the
beacons in question.

5) Crashes that occur away from the airports, where a search operation is
needed, probably involve a very small percentage of pilots and passengers
over their lifetimes. I really don't know how small that percentage is; but
if the percentage is as small as I suspect, then there is some question
about whether any system makes sense--with the exception of post crash
beacons in aircraft carrying passengers commercially and possibly combat
aircraft. (If the lifetime probability, for the participants in the
activity, is only one or two percent, then it is long past time to reopen
the debate about general aviation fleetwide use in terms of its value versus
cost in money, time, effort, freedom and privacy.)

Peter