Backup gyros - which do you trust?

I thought one of the reasons for the turn coordinator is that it won't tumble in
unusual attitudes where the AI will. I once tumbled my AI in IMC, and it was
not a pretty thing. Gave me a real bad sense of vertigo. At the time I had a
needle and ball rather than a TC, but that was the instrument that let me sort
things out. I think I would still want either a T&B or a TC in my primary scan.

Richard Kaplan wrote:

Put it where the turn coordinator is located and the put the turn
coordinator off to the side somewhere.. the regs say you must have a turn
coordinator but do not say where the turn coordinator has to be on your
panel.


--
--Ray Andraka, P.E.
President, the Andraka Consulting Group, Inc.
401/884-7930 Fax 401/884-7950
email
http://www.andraka.com

"They that give up essential liberty to obtain a little
temporary safety deserve neither liberty nor safety."
-Benjamin Franklin, 1759

Newer vacuum AIs have warning flags, dual vacuum pumps, and vacuum warning
lights on the annunciator panel. If I had an electric AI and a vacuum AI and
they disagreed markedly, I would be suspicious of the one having warning
lights and flags all over it.

Otherwise, comparing them to the other instruments, as you suggested, is the
best approach. AOPA Safety Foundation just ran some tests on how long it
takes a pilot to recognize that his vacuum system has failed, and how long
it takes pilots to recover from those failures. Many times it took over 90
seconds, which is way too long. Some never did recognize the failure.
However, none of them were convinced that the vacuum instruments were
working and that it was the other instruments that had failed. IIRC somewhat
less than half discovered the problem quickly and took quick action. Only
about 1/4 of them covered the failed instrument.

On 13-Jul-2003, Ray Andraka wrote:

The problem isn't just finding a home for it, it is finding a home for it
that is in a spot where it will be in the pilot's primary scan. I don't
think
it would do much good on the other side of the panel where it might only
be
referenced once a minute or less.


Our Arrow has a backup electric AI on the right side of the panel. It is
turned on whenever I am in or near IMC. I do not include it in my primary
instrument scan, but check it periodically to make sure it is on and stable.
I have fortunately never had a failure of my vacuum AI in IMC, but I have
practiced under the hood with the vac AI and DG covered, using the electric
AI for guidance. For me, it only takes a few seconds to get comfortable
with looking across the panel, and sure beats sweating bullets trying to
hold attitude and a reasonable course with only the TC, particularly in
turbulence.

So, the only issue is whether I could detect a failed vac AI before it leads
me (or the autopilot) into an unusual attitude. If the problem is (as is
most likely) a vacuum pump failure, I have a vacuum warning light right in
front of my eyes that would be hard to miss. But a failure of the gyro
itself could be trickier. I tell myself that if I can't keep a reasonable
course (per the DG) with a wings-level attitude (per the AI), then something
is wrong and I need to immediately refer to the TC and the electric AI to
sort things out.

-Elliott Drucker

Ray Andraka wrote:
Personally, I think the instrument scan typically taught relies too
heavily on the AI given its relatively low reliability.
Unfortunately, the alternative is a scan that works a bit more like a
partial panel scan using the AI as supporting, not primary. Such a
scan is much harder to master and requires considerable finesse to
keep from chasing the needles. It is not one I would expect to be
able to teach someone just learning to fly by instruments.

You are probably right. When I did my initial IFR training, my
instructor was very big on partial panel work. As a result, I learned
to not rely on the AI, and I find partial panel approaches (in training,
anyway) almost a non-event.

The downside, is that I suspect I don't use the information the AI gives
me as much as I should. I tend to fly pitch by airspeed, not by the AI.
This probably makes me not as smooth and precise as I might otherwise
be. But I do have a lot of confidence that I can fly an approach on the
TC and ASI alone.

James Robinson wrote:

One comment in the report was that the pilot might have had a tendency
to focus on a single problem, and mot paid attention to other things.
He could have been trying to troubleshoot the electrical problem, and
not handed control over to the copilot, who would have had a better view
of the remaining functional instruments.

This is poor CRM if it is the case.

Did the report say anything about the training of the pilots? I
woulda thought they did regular sim stuff, where I assume the
instructors put you through the wringer on various failues.

The failure would have been immediately obvious, so
it wasn't one of those insidious failures that people don't notice at
first. An experienced IFR pilot should have been aware of the need to
maintain attitude and yet lost control almost immediately. In reading
the report, it seems like such an avoidable accident, yet...

Yeah, that's what gets me about so many of these.

Sydney

Roy Smith writes:

The downside, is that I suspect I don't use the information the AI gives
me as much as I should. I tend to fly pitch by airspeed, not by the
AI.

Are you sure that using the ASI for pitch doesn't make you smoother?
I think that a couple of knots difference is more noticeable than a
fraction of a degree change in the AI pitch indication.

My problem is that managing pitch with the ASI gets hard in turbulence.


All the best,


David

--
David Megginson, , http://www.megginson.com/

C J Campbell wrote:
Newer vacuum AIs have warning flags, dual vacuum pumps, and vacuum warning
lights on the annunciator panel. If I had an electric AI and a vacuum AI and
they disagreed markedly, I would be suspicious of the one having warning
lights and flags all over it.

CJ,

How do newer vacuum AIs come with dual vacuum pumps?

We have a "warning flag" on our newer AI. I note that it is really
a low vacuum flag. It doesn't say a thing about how reliably the
instrument itself is operating.

Sydney

Ray Andraka wrote:
There are several things you can add to help with the identification, In my
plane I have a low vacuum warning light (part of the precise flight backup)
mounted between the AI and DG. The AI is one of the sigmatec ones with a vacuum
flag, so that if vacuum is lost in the instrument but not in the system I still
know about it right away. These warnings cover identification of the more
common cause of loss of the AI. The other failure mode would be failure of the
gyro, in which case I don't believe you get the insidious gradual spin-down like
you do with loss of vacuum.

Ray,

I'll speak to the latter.

A failing horizon gyro may not "spin down". But it can still
be insidious. Example: our AI had a period where, in level flight,
it would jump up and indicate a rather nose-high attitude. Fail
to catch it and you'd be in a rather steep dive. Then it would
go back to normal. Then jump up again....finally it broke and
unmistakably started spinning in a nauseating fashion, but the
"breaking" process could easily have caused a loss of control for
a pilot w/out a good cross-check (our failure happened VMC)

Cheers,
Sydney

Richard Kaplan wrote:

Put it where the turn coordinator is located and the put the turn
coordinator off to the side somewhere..

N. F. W.

I think it's time I had a really, really, good hunt for
that post about the Grumman getting flipped upside down
and dumped into IMC after (what was probably) a collision
with an RC plane.

Those Electric and Vacuum AIs come with a get-your-life-back
guarantee they honestly, really truly, won't tumble, never ever,
no matter what, even if I do? How do I test it, in a non-aerobatic
plane not approved for spins?

Cheers,
Sydney

C J Campbell wrote:
Newer vacuum AIs have warning flags, dual vacuum pumps, and vacuum warning
lights on the annunciator panel. If I had an electric AI and a vacuum AI and
they disagreed markedly, I would be suspicious of the one having warning
lights and flags all over it.

I just bought a new AI this spring. For an extra $50 or so you can get
the one with the flag. Since I already have the EI volts/amps
instrument that has warning lights for both high and low voltage, but no
warning light for the vacuum pump, I spent a little extra for the flag.
Now I don't need a suction warning lamp.