Standby Vacuum?

Michael wrote:

I think that if you really feel the need for redundancy, the sensible
solution is replacing the T&B with an electric AI.

I see that Sporty's is encouraging this option, too, with their electric
AI.

However, doesn't the AI have the potential to tumble in an unusual
attitude? During my IFR training I recall learning that the turn
coordinator will not tumble in an unusual attitude scenario whereas the AI
may. Since recovery from an unusual attitude was taught to me by first
going to the TC, I would be hesitant to replace an instrument so reliable
during a UA.

What say you?

--
Peter
























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However, doesn't the AI have the potential to tumble in an unusual
attitude?

You know, I've heard that too. And it sure seems like it could, by
design. Only thing is, I've spent a lot of time teaching unusual
attitudes - and I've never seen it happen. I think you need something
more radical to happen than what we think of as an unusual attitude -
more aerobatic.

I see little chance of that happening with dual AI's, and even less
chance that the average pilot will recover from an aerobatic attitude
partial panel after screwing up enough to get into that mess.

But hey - if you have the panel room, why not keep the electric TC too?

Michael

Michael wrote:

I see little chance of that happening with dual AI's, and even less
chance that the average pilot will recover from an aerobatic attitude
partial panel after screwing up enough to get into that mess.

Interesting that you pointed that out. I was thinking the same thing when
I posed the question but thought that two tumbling AIs would pretty much
guarantee that the pilot would not recover.

But hey - if you have the panel room, why not keep the electric TC too?

My Bonanza has the original TC along with a backup electric AI located to
the left of the TC. However, the electric AI keeps precessing and requires
a reset about four times per hour, which concerns me.

--
Peter
























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Interesting that you pointed that out. I was thinking the same thing when
I posed the question but thought that two tumbling AIs would pretty much
guarantee that the pilot would not recover.

I agree with you - with two tumbled AI's and no TC, recovery is
impossible. With a working TC, it is merely highly unlikely.
Therefore, if the panel space is there, it might make sense to keep the
TC. Not much sense, mind you, because if you manage to screw up badly
enough to put the plane into an attitude that would cause both AI's to
tumble, well, I'm willing to give very good odds that you're not going
to recover on the TC.

However, let's say having both the TC and the second (electric) AI is
not practical (probably due to space considerations). Would I rather
have an electric AI, or the TC? I would still prefer the electric AI.
First off, with dual AI's next to each other, I believe that following
a dying AI into an unusual attitude becomes far less likely, and thus
while the chances of recovery from the unusual attitude are reduced
slightly, the chances of encountering it in the first place are reduced
dramatically. Not so with a backup vacuum - you have to engage it.
And even if you do, half the time (in my experience more) the problem
is the AI, not the power source, so backup power for the AI does you no
good.

The problem with this analysis is the reliability (or lack of same) for
electric AI's. I've heard the affordable ones are not good, and the
good ones are not affordable.

Finally, there is the issue of training. If you have dual AI's with
independent power sources, it makes sense to skip partial panel
training. If you have only a single AI, even with redundant power
sources, that's not the case. In that case, a standby vacuum system
seems to be an unjustified expense - the money spent on it is probably
better spent on recurrent training.

Michael

Therefore, if the panel space is there, it might make sense to
keep the TC.

I know that FAR 91.205 requires a rate of turn indicator for IFR (except for
airliners with three attitude indicators). Is it common for this requirement
to be waived to allow substituting a second AI for the TC?

I know that FAR 91.205 requires a rate of turn indicator for IFR (except for
airliners with three attitude indicators). Is it common for this requirement
to be waived to allow substituting a second AI for the TC?

In a manner of speaking. No waiver is actually necessary. Advisory
Circular 91-75 details the conditions under which this substitution is
acceptable. Note that 91.205 states:

no person may operate a powered civil aircraft with a standard category
U.S.
airworthiness certificate in any operation described in paragraphs (b)
through
(f) of this section unless that aircraft contains the instruments and
equipment
specified in those paragraphs (or FAA-approved equivalents)

91.75 Details what constitutes an FAA-approved equivalent for a
rate-of-turn indicator.

Michael

Michael wrote:

First off, with dual AI's next to each other, I believe that following
a dying AI into an unusual attitude becomes far less likely, and thus
while the chances of recovery from the unusual attitude are reduced
slightly, the chances of encountering it in the first place are reduced
dramatically.Â*Â*NotÂ*soÂ*withÂ*aÂ*backupÂ*vacuum *-Â*youÂ*haveÂ*toÂ*engageÂ*it.

This is the first of my two major reasons for preferring the backup AI. It
helps with problem detection. A backup vacuum doesn't.

And even if you do, half the time (in my experience more) the problem
is the AI, not the power source, so backup power for the AI does you no
good.

And this is #2.

Some people to whom I've spoken about this have made a big deal about the
fact that the backup AI does nothing for a HI during a vacuum failure. My
response is typically "who cares?". Given a compass and a GPS, the HI has
plenty of backup already.

- Andrew

Andrew Gideon wrote:
Michael wrote:

First off, with dual AI's next to each other, I believe that following
a dying AI into an unusual attitude becomes far less likely, and thus
while the chances of recovery from the unusual attitude are reduced
slightly, the chances of encountering it in the first place are reduced
dramatically. Not so with a backup vacuum - you have to engage it.

This is the first of my two major reasons for preferring the backup AI. It
helps with problem detection. A backup vacuum doesn't.

Which is why the Precise Flight standby systems include a low-vacuum
annunciator light.

-cwk.

Which is why the Precise Flight standby systems include a low-vacuum
annunciator light.

Which merely gives you a false sense of confidence as the vacuum stays
on and the AI fails.

Since AI's fail as often as dry pumps (and far more often than wet
pumps) the low-vacuum annunciator light really doesn't help much.

The real solution would be a tiny magnet integrated into the vacuum
gyro and a tiny coil fixed in place. This would act as a generator,
and would likely make enough juice to keep an LED lit. LED goes out -
problem. Doesn't matter whether it's a failed AI or failed vacuum.

Now good luck getting that certified for GA at any sort of reasonable
price.

Michael

Peter R. wrote:
Michael wrote:


I see little chance of that happening with dual AI's, and even less
chance that the average pilot will recover from an aerobatic attitude
partial panel after screwing up enough to get into that mess.


Interesting that you pointed that out. I was thinking the same thing when
I posed the question but thought that two tumbling AIs would pretty much
guarantee that the pilot would not recover.


But hey - if you have the panel room, why not keep the electric TC too?


My Bonanza has the original TC along with a backup electric AI located to
the left of the TC. However, the electric AI keeps precessing and requires
a reset about four times per hour, which concerns me.


What brand ?