Backup gyros - which do you trust?

Ray Andraka <ray@andraka.com> 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.

Ray Andraka <ray@andraka.com> 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

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.

Richard Kaplan wrote:

> A vacuum faliure with a gradual spooldown of the AI and DG at vary rates is
> a subtle process, very different from having an instructor suddenly cover up
> a gyro. You are correct that there is enough redundancy in a typical GA
> plane to FLY partial panel; the problem is that there is not enough
> information for most pilots to IDENTIFY a partial panel situation before the
> situation has become critical.

Richard,

There seem to be a number of instances where the pilot was aware
of the problem -- had described it to ATC and possibly requested
some form of assistance -- had been flying the plane for some time
more or less under control, and then lost it. So the pilot did
identify a partial panel situation before it became critical,
he simply couldn't FLY partial panel.

The accident Julian posted the link for more-or-less seems to
fall into this case, as did a couple of local accidents.

Cheers,
Sydney

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

<e.drucker.remove@> wrote in message
news:vaAQa.15123$D%1.14303@nwrddc01.gnilink.net...
> ... 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

Sydney Hoeltzli <last_name@swbell.net> 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 . 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