Robert M. Gary wrote:
After having both a vac pump failure and an AI failure (not on the
same flight ) I decided its really time for a backup. I always
consider my Mooney to be an "IFR anytime" type of plane, in that I
consider it a solid IFR platform. When the vac pump goes out alarms
starting sounding, my voice annunicator starting saying "check vac
pressure" and the needle goes to 0. It's pretty obvious. I do a
voluntary IPC every 6 months with a local DE and always do partial
panel approaches so I'm as comfortable as you can be with that. A
couple weeks ago I had my AI go out. WOW, that's another story!! The
thing slowly rolled 30 degrees off and REMAINED RESPONSIVE!! When I
banked, it banked, when I pitched, it piched. Figuring out that it was
dead could be hard and it would be easy to miss it. I decided I need a
back up and those vac backup systems are a waste of money(Precise
Flight, electric vac, etc). After getting it back from overhaul my
partner reported that it did it again! I called a couple gyro places
and they said the vac AIs don't last very long because they have a
stream of "dirty" air running through them. The electrics last much
longer. So I'm getting an electric AI installed as my backup. I
noticed that the non-TSO'd electric AIs are almost $1000 less than the
TSO'd ones. I asked my mechanics and the FSDO and they said I could
probably get a 337 approved by the FSDO for a non-TSO'd unit as long
as it wasn't in the "T" area of the panel. One FSDO guy said I might
need to label it "VFR only" and I'd have to promise not to do 135. In
either case I'll end up having an electric backup AI for under $1500.
That's less than the price of a backup electric vac pump installed
about about the same price to put a Precise Flight in a Mooney (with
California labor rates of $95/hr ) with twice the redundency.

FWIW, I have an electric AI in my Mooney and I wouldn't do it again. It's
expensive, failure prone, and too far out of my scan to be useful as a backup.

I've had the Precise Flight system in a previous airplane, and it was OK, but
has some drawbacks. Since it depends on the intake manifold as a vacuum source,
the vacuum available is dependant on throttle setting. In order to maintain
vacuum for the instruments, you may need a throttle setting that's not what
you'd prefer.

I now have the Aero-Advantage STCed dual-rotor vacuum pump and think it is
overall the best solution. It offers more redundancy and more reliable backup
for a reasonable price. http://www.aeroadvantage.com

Including installation it will be less than your electric AI, and a better
solution, IMO.

Dave
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