Ron Natalie writes:

Driving gyros with air pressure is much simpler, cheaper, and
more reliable from the gyro point of view than using small electric
motors. Venturis and engine-driven wet pumps are real reliable
and not too expensive too. The major problem is engine-driven
dry pumps which have a nasty habit of failing unexpectedly.

Which types of pumps are used in most modern small aircraft?

There are some real nice units coming on the market these days with
a electric Attitude Gyro with a battery backup. But they are still
MUCH more effective. You can actually have two engine driven vacuum
pumps for redundancy in many cases and two independent gyros for what
they cost.

How many small aircraft have redundant pumps and gyros?

Are any small aircraft using RLGs?

Anecdotally, I've had perhaps a half a dozen electrical failures in
several different aircraft over the years. I've had one dry pump
go on me.

How hard is it to spot a pump failure? I've gotten the impression from what
I've read here and elsewhere that vacuum pumps may fail gradually and
insidiously, whereas (presumably) an electric motor fails in a much more
obvious way.

One major issue with the vacuum failure and transition to parital panel
is realizing that the gyros have failed. While IFR pilots are taught
to contantly verify the indications between the various instruments
a prominate failure flag or annunciator is a big help.

Does a failure involve the gyro coming to a stop, or can it just slow down and
thereby cause problems?

Frankly, the IFR GPS really makes partial panel a lot easier. Zoom
up the thing so you can instantly see any track changes and watch the
altimeter and you'll find it's not too rough maintaining flight.
Punching the autopilot on is almost cheating.

But how does that help you if the AI has failed? The GPS wouldn't tell you
the attitude of your aircraft.

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