I don't agree that that's the best answer. Don't get me wrong, I enjoy
partial panel practice, and have always maintained good proficiency with
it. Compass turns are, well fun, but I'd be hard pressed to say much of
anything else good about them. Timed turns work out much better, if
you're in any kind of shape, but the OP is correct that a redundant AI
really is the best solution, and I would even say highly recommended for
any plane with a vacuum driven AI that is to be used in actual
IFR/IMC.Those planes are getting older now, and many vacuum pumps have
not been replaced in years.

One of the most important choices is not what you buy (there are now a
number of good devices on the after-market) but WHERE you put it.Over on
the far edge of the co-pilot's seat is not the right place. In place of
the turn coordinator is good if you have limited panel space, otherwise
just as close as possible to the original AI. One of the best things
about a backup AI is not just that you have something to use when the
vacuum-driven device fails, but that it actually points up this failure
before it happens. If you can see both at the same time, you can see
when they start to disagree - and many AI or vacuum failures are slow,
progressive events. If you start to see your two AI's out of lock-step,
start making sure you've got both in your scan. Gives you a lot more
time and comfort to run those textbook quizzes "which instrument is
lying?"!



In article
,
says...

Jerry, the most reliable thing you can do is to stay proficient with
your partial panel skills. Vastly underutilized is the magnetic
compass, too. Go fly an approach or two under the hood partial panel
and you'll soon appreciate how little you really need to control the
airplane.