wrote:
Flying a very nice, new (2000) rented 172SP, there was a pop, the
audio panel went dead, and then an acrid odor in the cabin.

If it turns out to be the panel that failed, and depending on the
warranty policies of the panel manufacturer, it might be interesting
if the aircraft owner can get a local tech to open up the panel.
This is within the date range of a big batch of bad capacitors; they
are most famous for failing on PC motherboards, but they have turned
up in lots of places: http://en.wikipedia.org/wiki/Capacitor_plague

After the couple seconds of stark surprise I flipped the avionics
master off. When it appeared there was no real smoke and the smell
disappated I tried cycling the master. Nothing bad, but no audio
panel (completely dead) and thus no radios.

Disclaimer: This is based on very limited experience with audio panels
(real panels, but installed in simulators) a few years back. I thought
some panels had a default "bypass" mode. In other words, under certain
conditions, it connects the pilot's earphones/mic/PTT to COM 1 and
that's it. You don't get an intercom or the Dolby 5.1 surround from
the DVD player or anything else, but you can use one of your radios.

The way to get into this mode probably varies. Simply shutting off the
audio panel might do it. If the "bypass" is implemented with an
electromechanical relay, it should even still work under many of the
failure conditions of the audio panel - if the power to the relay coil
drops out, the contacts will make the default connection. On an older
panel with the "only one at a time" mechanical switches on the front,
pushing one of the switches in halfway and then releasing so that none
of the switches are pressed might do it. The manual (or careful
experimentation) may help.

If audio panels _don't_ do this, or if the old ones did but the new
ones don't, I wonder if it would be useful to have a headset jack that
connects directly to COM 1 and doesn't go through the audio panel. That
way, if you lose the panel but not the radio, you can plug your headset
into the "direct" jack and still use COM 1. I realize you don't get to
add your own jacks to a rental plane - this is more of a general "would
this be useful" question.

1) ALWAYS have handheld with me.

A couple of people have mentioned having good batteries in it as well.
If you want to be able to just pick up the handheld and talk, this may
not work very well. Also, none of this stuff is as critical as a backup
radio in an airplane. Having said that, I have a couple of portable
devices that I run NiMH AA batteries in. What I do is to have a couple
of sets of NiMH and a fresh set of alkalines. If I go through both sets
of NiMH, I can then put in the alkalines while I decide what to do next.
The alkalines don't mind sitting around for a few months doing nothing,
and if I haven't used them after several months, I'll use them somewhere
else and get a fresh spare set of alkalines for the portables.

Matt Roberds