M wrote:
I'm considering adding a second (backup) electric AI. The primary AI
is vacuum driven so is the DG.

Two questions:
1. Does adding a backup electric AI require an 337?
Yes

2. Does the electric AI needs to be TSO'ed?

In general it needs to be TSO'd or STC'd. I've looked into this myself.
There are some very good units out there for the homebuilt market that
are the same as our TSO'd units for 1/4 the price. I did get one guy at
the FSDO to agree to consider signing a 337 on it if..
1) The unit was on the pax side,
2) The unit was for "entertainment" only and
3) The unit was labled for VFR only
4) I promised to never do 135 in my plane.


The plane will be used strictly for part 91 operations.

Thanks!

-M