backup for vacuum pump/attitude indicator failure

I would be skeptical that the derived attitude indications based on GPS
course, speed and altitude changes would be
sufficient in an upset. A vacuum failure can be insidious and the airplane
will likely be in an unusual attitude
before you deduce the problem. I would be curious if anyone has
experimented with this in earnest.

The MTBF of a dry pump may be as low as 400 hours. I believe the backup
electrical AI can be used as a replacement
for your turn-and-bank indicator. I do not have one, but it would afford a
tremendous piece of mind and I am convinced
your scan would pick up the inconsistency sooner than the cross check
afforded by the standard six pack. Our aircraft have
an electric backup vacuum source (which would require you to recognize the
failure and flip the switch). The electric
source does not generate the minimum 4.5lbs/in/in but I have never
investigated how this might affect the instrument
performance.

Regards,
Todd

Concerning the scan to recognize a failure...In addition to the
backup, Precise Flight also offers a lamp that is triggered by
vacuum pump failure. An immediate warning rather than waiting to
discover it. True, it doesn't offer any redundancy, but minimizes
the time to identify a problem.

Of course I recognized my AI failure immediately -- I was turning
right and the AI turned left....

My Husky had a really nice minimal IFR panel. A KX155 Nav/Com, a King
KLN90B (with its own seperate CDI), and a Century I autopilot that was
all electric and worked off the turn and bank. Loose the electric and
you still have the DG and AI. Loose the vacuum and you still have the
autopilot and the turn coordinator AND the GPS (which can work as a DG,
sort of). Top that all off with a handheld radio (with its own antenna)
and a handheld GPS (with it's own permanently mounted outside antennae)
and its pretty damn backed up.

I have the precise flight setup. I've never had to use it but, my sense
is that the vacuum failure light may be the most valusable component.

Blanche wrote:
Concerning the scan to recognize a failure...In addition to the
backup, Precise Flight also offers a lamp that is triggered by
vacuum pump failure. An immediate warning rather than waiting to
discover it. True, it doesn't offer any redundancy, but minimizes
the time to identify a problem.

Of course I recognized my AI failure immediately -- I was turning
right and the AI turned left....

Maule Driver wrote:
I have the precise flight setup. I've never had to use it but, my sense
is that the vacuum failure light may be the most valusable component.

The light is good if you don't have one.

----
Directed to the OP (I'm sure MD knows this):
If you go with the Precise Flight, be sure you check the shuttle valve
frequently as described for preflight in the POH Supplement. The shuttle
valve can stick and then when you need it, it doesn't work. Just the act
of checking it causes the valve to operate and probably helps keep it
from sticking.

Also be sure you understand the operating limitations - altitudes and
power settings where it works and doesn't.

On Mon, 20 Nov 2006 13:43:01 -0500, Dave Butler wrote:

Also be sure you understand the operating limitations - altitudes and
power settings where it works and doesn't.

I have to say: I don't like this system. One time when you want happy
gyros is when low and busy...like on a missed approach. But the
full-throttle of the missed means that the gyros are spinning down.

Plus, of course, there's the fact that it does nothing for an AI or
plumbing failure.

- Andrew

Blanche wrote:
Concerning the scan to recognize a failure...In addition to the
backup, Precise Flight also offers a lamp that is triggered by
vacuum pump failure. An immediate warning rather than waiting to
discover it. True, it doesn't offer any redundancy, but minimizes
the time to identify a problem.

Of course I recognized my AI failure immediately -- I was turning
right and the AI turned left....

The concern about noticing a failed pump quickly is one of the reasons
I got the voice annunciator system. That and the gear warning horn is
hard to distinguish from the stall horn. I now have something like 8
channels hooked up and I like it.

-Robert