Backup gyros - which do you trust?

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/

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:

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

"Sydney Hoeltzli" wrote in message
...

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

No doubt there will always be crashes we cannot avoid. I am sure there are
people with tip tanks who run out of fuel; that does not mean tip tanks fail
to increase an airplane's range.

The fact is that any sim instructor will tell you many pilots have a
difficult time identifying gradual loss of the vacuum system and that
redundant gyro equipment helps to identify this failure earlier.

--
Richard Kaplan, CFII

www.flyimc.com