Backup gyros - which do you trust?

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.

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

"Sydney Hoeltzli" wrote in message
...
| 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?
|

They come with a new airplane attached to them. Not unlike the $350,000
Cessna ball cap I bought.

Sydney Hoeltzli writes:

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.

Yup, I had one freeze but the vacuum was fine so it didn't complain.

--kyler

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.

Dan Luke wrote:

This is a very interesting issue, to me. Reading the records of IMC
loss-of-control accidents is very unsettling to this single pilot IFR flyer
because of the cases where there *was* backup attitude instrumentation
available. Even when there wasn't, the pilots usually had at least the turn
coordinator to help keep the aircraft upright. It is too simple to chalk up
all these accidents simply to lack of proficiency. There is something else
going on - some human factors issue that has not been properly identified.

Concur. I, too, don't think it's entirely lack of proficiency. I think
there are pilots who have training and proficiency, who, in the words
of my CFI, "ought to be able to do it", who don't. And clearly backup
AI is no panacea.

Obviously I can look for consistency with other instruments -
does my DG or Turn indicator show I'm turning, does the VSI show a climb
or descent - but what would be the best strategy given the various ways
vacuum or electric driven instruments can fail?

Having an inventive CFI who has little habits like mind-f***ing
me into doubting my AI while palming the TC fuse, I think the best
strategy is delimited above. *Instrument cross check is essential*

Rod Machado's "Instrument Pilot Survival Manual" delineates something I
haven't seen elsewhe

Turn triangle of agreement: AI, TC, compass
Pitch triangle of agreement: AI, VSI, alt static on/off

The point is to deliberately cross-check instruments
which depend upon independent power sources.

The problem (for me anyway) in training is that my compass is
mounted on the windshield bow and it's impossible to keep it
in my scan in VMC under the hood w/out extensive "cheating".

I also think Machado's under-utilizes ASI and hearing. I
think the reasoning is that there are three sources of ASI
failure and only two for VSI, one of which alt static
eliminates. But when forced to fly instruments without static
instruments, I found hearing was a fairly precise means of
pitch control (at constant power for a fixed-pitch prop)

Interested to see what others say: this topic should elicit a
lot of opinions.

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