(Dave) wrote
My goal would be to put an elec. AI and HSI in the panel, dump the two
vacuum guages and also dump the vacuum pump (some weight savings!).
Has anyone done this successfully?

Depends on what you mean by successfully. I know people who have done
it. I consider their installations to be adequate for day-VFR only.
However, the FAA does not concur.

First off, you're getting a lot of bad info here. There is NO
requirement for redundancy for IFR under Part 91. It's perfectly
legal (though not too smart) to have all three required gyros powered
from the same non-redundant source. In fact, it used to be pretty
common to have airplanes that were IFR certified equipped with all
three gyros driven by vacuum. The TriPacers with the advanced panel
actually came that way from the factory.

Second, it's a very rare light airplane that is certified with any
gyros at all as required equipment. Ditto the vacuum pump. On most
of the GA fleet, it's perfectly legal to remove ALL the gyros AND the
vacuum pump and not replace them at all. Only thing is, you can't fly
IFR that way - but that's a part 91 requirement, not a maintenance
issue.

However, just because something is legal does not mean it won't cause
you grief - especially something as dumb as making all your gyros
electric and driven by a single electrical bus. The way to make this
happen is to submit two Form 337's, a couple of weeks apart and under
separate cover.

The first form would list the removal of the existing gyros and the
installation of the new gyros by model number. The second form would
list the removal of the vacuum gauges and vacuum pump, and the
installation of a cover plate over the accessory pad. Either one by
itself will raise no eyebrows, but combining everything can cause some
fed who doesn't actually know the rules but thinks he does (much like
some people who posted here) to make your life difficult.

Good luck, and I hope your master contactor doesn't decide to go TU in
IMC.

Michael