Backup gyros - which do you trust?

On 14-Jul-2003, Roy Smith wrote:

Not really. When I'm doing partial panel work, I find I miss the DG
much more than I miss the AI.


A yoke-mounted GPS in either HSI or moving map mode is a good substitute for
a failed DG. Strictly for "situational awareness" of course! You have to
be careful in that the update of the GPS display is not instantaneous like
the DG's response to heading changes, so it's easy to find yourself "chasing
the needle". That's where the backup AI comes in.

Why do you think leaving it off most of the time will extend its life?

wrote in message
...
... We leave [our electric AI] off when flying in solid
VFR conditions, with the understanding that this will extend its life. So
far, so good. It's required no maintenance in over 7 yrs/1400 hrs (knock
on
wood).

-Elliott Drucker

I thought that gyro bearings were very susceptible to damage if subjected to
mechanical shock while not turning. If that is true, then turning it off in
flight may actually reduce the service life.

wrote:

In our plane, this installation also allowed plenty of space to install an
ON/OFF switch next to the electric AI. We leave it off when flying in solid
VFR conditions, with the understanding that this will extend its life. So
far, so good. It's required no maintenance in over 7 yrs/1400 hrs (knock on
wood).

-Elliott Drucker

--
--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

On 14-Jul-2003, "Jon Woellhaf" wrote:

Why do you think leaving it off most of the time will extend its life?

Seems to me that the two wear items in the electric AI are the brushes in
the DC motor and the gyro bearings. Also seems logical to me that both will
wear a lot less when not turning. As noted in previous post, this strategy
seems to be working for us. I would certainly entertain contrary wisdom
from anyone with more specific knowledge.

-Elliott Drucker

Sydney Hoeltzli wrote
What do you think of the conclusions? They seem to be:
1) prevent AIs from failing

Well, there's a lot to be said for that. For one thing, it's far from
unlikely that BOTH of the AI's failed, not just one.

Did you miss this: (All quotes from the referenced report)

"These 21 artificial horizons had an MTBUR of 257 hours." That's mean
time before unscheduled replacement, but... "The artificial horizon
fitted to the EMB-110had no specified overhaul life and was treated as
an 'on condition'item" and thus all replacements were unscheduled.

Why was such a shockingly high failure rate tolerated? Well, "The
BCAR Section under which the aircraftwas certificated did not
stipulate the reliability requirementsthat the artificial horizon
should meet in order to ensure thatthe occurrence of a double failure
was a statistically remoteevent." Gotta love the way those regs
protect us...

And sure enough it was not statistically remote - it had happened
before! "An EMB-110 operated by another UK company suffered two
double artificial horizon failures in 1995. The first,on 4 June 1995,
involved a double instrument failure" There were only a handful of
EMB-110's in the UK...

2) since 2 AIs weren't enough to keep the plane upright (combined
with 2 turn and banks, 2 of every other instrument), require
passenger planes to have 3

Yes, that's the recommendation. IMO it's unmitigated crap. First
off, AI's should not be failing at an average of less than 300 hours.
Second, there were still two good PNI's (basically HSI's) and
turn&slip indicators. But could the pilots use them? Probably not
because "This technique, commonly referred to as 'limited panel' (see
paragraph 1.5.3.2) does not form part of a professional pilot's
recurrency training and testing."

So the most likely causes of the crash are AI failure (quite possibly
double AI failure), and the inability of the flight crew to fly
partial panel because SURPRISE they get no recurrent training in
partial panel flying. Exactly what kind of outcome could one expect
when you fit proven failure-prone AI's to an airplane and don't give
the flight crew any recurrent partial panel training?

(agree, chilling)

There are plenty of chilling accidents out there. This isn't one of
them. This was inevitable.

Michael

wrote in message
...

seems to be working for us. I would certainly entertain contrary wisdom
from anyone with more specific knowledge.


Well my understanding from the last shop which overhauled my AI was that if
an AI can be caged then it should be shipped in the caged position because
it can be damaged if transported uncaged.

Perhaps the same logic applies to flyingwith an uncaged and unpowered gyro,
but I cannot give any other source except the above.

--
Richard Kaplan, CFII

www.flyimc.com

On Sun, 13 Jul 2003 22:10:08 -0400, Roy Smith wrote:

David Megginson wrote:

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?

Well, for example, on my initial climb, I'm looking for Vy on the ASI.
Since I'm approaching Vy from below, it means I have to just sort of
guess at the right pitch and watch the ASI to see what the airspeed
does. The "right" way is to know what pitch attitude I want, peg the AI
there, and then watch the ASI to confirm I'm getting the performance I
expected.

I guess I don't agree with the "right" way then. The pitch attitude for Vy
(or any other airspeed) will be somewhat dependent on aircraft weight,
density altitude, etc. I do exactly what you do, use the ASI as my climb
attitude reference, not the AI. Same for descents -- I peg whatever
airspeed i want, keeping the rpm's where I want them, and then make sure
that I have a reasonable descent rate using the VSI. Adust pitch as
necessary to keep everything where it should be.


I know I do it wrong, and I make a concious effort to retrain my scan,
but it's very difficult to unlearn the way you first learned to do it.

In rec.aviation.owning Roy Smith wrote:
: David Megginson wrote:
: But once you're established, do you find it easier to hold pitch using
: the ASI?

: Not really. When I'm doing partial panel work, I find I miss the DG
: much more than I miss the AI.

I totally agree with Roy here. I also don't use the AI as much as some. I too
fly pitch using the ASI, although I use the AI as a reference to set pitch
during level-offs. I too miss the DG more than the AI in partial panel
work. I do fly a fixed-gear Cherokee, though.

As an aside, I had an AI failure in IMC, on the 3rd or 4th flight after
I bought my plane. I didn't realize the AI was a little slow to align at
startup- I had only owned the plane a couple hours!
In flight, I noticed the AI leaning a couple of degrees and thought "Oh,
the AI isn't installed in the panel straight- the DG isn't turning."
About 30 seconds later, the AI started spinning in the roll axis. At
perhaps 600 degrees a second! This was pretty easy to diagnose.
The next day (VFR) the AI worked fine. It was very sensitive to temperature,
and having cold-soaked overnight at Will Rogers World, it just wasn't
happy.

PS, modern AI's won't tumble in roll, and should not tumble until
more than +/- 85 degrees of pitch. (REF the R.C. Allen install guide.)
--
Aaron Coolidge (N9376J)

Bob Gardner wrote:
You have three sources of bank information in a typical panel: the attitude
indicator, the turn coordinator, and the heading indicator.

Um, isn't this leaving out something fundamental (and pretty
reliable, if difficult to interpret)?

Sydney (Be Expert With Map and Compass)

"Roy Smith" wrote in message
...

Are you sure that using the ASI for pitch doesn't make you smoother?

Well, for example, on my initial climb, I'm looking for Vy on the ASI.
Since I'm approaching Vy from below, it means I have to just sort of
guess at the right pitch and watch the ASI to see what the airspeed
does. The "right" way is to know what pitch attitude I want, peg the AI
there, and then watch the ASI to confirm I'm getting the performance I
expected.

I think it depends on the aircraft. Flying a simple trainer on trends in
the secondary instruments is not too hard. The more slippery the aircraft,
the more difficult it becomes: by the time you've picked up the trend in the
ASI needle, your attitude is already in a mess. I noticed this
transitioning to the Mooney, and I think it's much more marked in faster
aircraft -- one of the reasons why jet pilots don't spend a great deal of
time practising partial panel but rely on multiple AIs for redundancy.

Julian Scarfe