AI sometimes slow to come up to speed

[Peter R.[_2_]]

My attitude indicator was last replaced back in November 2006 with a
Mid-Continent overhauled unit. Since then I have flown on average
twice every single week of flights an hour or less in duration. Thus,
there are about 180 hours or so on this air-driven AI but it is out of
warranty.

Around ten flights ago I noticed the AI, which normally rests in
almost level mode and spins right up at avionics-on, was resting with
an indication of 50 degrees off level. When I started the aircraft
and turned on the avionics the AI remained this way for perhaps 5
minutes before finally migrating to a fully erect and level mode.
The unit remained proper for the rest of the flight.

For the next three flights the AI spun right up when the avionics were
switched on but this behavior again returned twice over the following
five flights. So far it has not happened on two consecutive flights.
The aircraft is equipped with a back-up electric AI.

Is this a sign that the AI needs to be replaced again so soon after it
was installed or could this be something related to the air filter,
pump, or piping connecting the AI to the pump? The fact that the
problem is not happening every flight makes me wonder if this issue is
not directly caused by the AI dying. The only thing keeping me from
replacing it without question is its relative young age and low usage.

[Mike Isaksen]

"Peter R." wrote ...
> .... there are about 180 hours or so on this air-driven AI ....
>
> ... the AI, which normally rests in almost level mode and spins
> right up at avionics-on, ...

I'm confused by your details. You refer twice to expecting action at
Avionics Master On, but claim the AI is vac sourced???
Are you talking about your Vac driven AI (on with engine rpm) or your
electric backup AI (on with master, I've only seen these wired thru a CB,
never the avionics master)??
And the most important question: What is your vac gauge indicating?

[Peter R.[_2_]]

Sorry for the confusion. The AI to which I am referring is the
primary, vacuum sourced unit. The vacuum gauge is showing 4.5 inches
or so, which is steadily in the green.

[Mike Isaksen]

"Peter R." ...
> The vacuum gauge is showing 4.5 inches
> or so, which is steadily in the green.

OK, many A&Ps tweak the vac regulator toward the higher end of the range to
get a few more years out of a lazy gyro. Yours is running at the lower end.
Another bit of info you should have at hand (search in your logs) is when
the filter was last changed and the age (hours) of your Vac Pump. This will
save your mechanic the time to look it up.
Then you or your mech should get a good look behind the panel to make sure
the vac line for the AI is not pinched or kinked (sometimes happens at
install or after other work in done). This would make the AI get only a
fraction of the airflow needed.
Finally, keep a really close eye to see if the AI ever "hangs up" (even for
a second) once it comes alive after engine start. A "slow to awake" AI is a
annoying, any AI that "stops or stutters" once taxi or flight begings is
broken and downright dangerous.

[Peter R.[_2_]]

On Apr 12, 11:53 am, "Mike Isaksen" > wrote:

> OK, many A&Ps tweak the vac regulator toward the higher end of the range to
> get a few more years out of a lazy gyro. Yours is running at the lower end.

<snip>

Thanks, Mike. Lots of good information to check. Appreciate the
reply.