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

Just a little story about flying with failed instruments.

I was flying with an instrument student, and had been telling him the
importance of the gyroscopic instruments to maintaining control of the
airplane in the clouds. So I covered up one gyro, he kept flying along
fine. He was under the hood, we were flying mostly straight and level,
maybe some simple level turns, don't remember all the details now. Then I
covered up the second gyro. He kept flying along fine. So I covered the
third gyro, expecting him to soon wind up in a spiral dive. He kept flying
along fine. So finally I asked him how he was doing it. I had forgotten
about the GPS. He was watching the TRK number on the GPS, and that was
giving him essentially the same data as the DG, although with a slower
update rate. Along with the pressure instruments, he was doing just fine.




"Kelly" wrote in message
ups.com...
I would be interested in getting opinions about backup systems for a
vacuum pump failure and/or AI failure. I have a 172P with a single
vacuum pump system, standard instruments otherwise, and a Garmin 430.
I am most concerned about having a good backup if I lose a vacuum pump
or AI in IMC. I have been thinking about either a Garmin 396/496 or
the electric AI available from Sporty's. Looks like I could get a 396
or installed electric AI for about the same price ($2200 or so). While
I haven't seen the panel page/"6-pack" page on the 396 or 496, I have
read (in Aviation Consumer) that it's good enough to keep control of
the airplane in an emergency situation. Obviously, the 396/496 has a
number of other neat features such as inflight weather, terrain info,
etc. Any suggestions on which way to go with this.

BTW, I had also considered the Precise Flight backup vacuum system for
a while, and it certainly is cheaper (around $700 installed). However,
I was concerned by the fact that it would do nothing for you in the
event of failure of the AI vs. the primary vacuum pump.

Thanks.
Kelly

Kelly wrote:

I would be interested in getting opinions about backup systems for a
vacuum pump failure and/or AI failure.
..stuff snipped
Looks like I could get a 396
or installed electric AI for about the same price ($2200 or so). While
I haven't seen the panel page/"6-pack" page on the 396 or 496, I have
read (in Aviation Consumer) that it's good enough to keep control of
the airplane in an emergency situation. Obviously, the 396/496 has a
number of other neat features such as inflight weather, terrain info,
etc.

Funny you should ask. I covered up my AI and DG and tried flying via the
panel page on my 396. Downright freaky. I figured the lag would not be
too bad but it really does present a challenge. I suppose with practice
it might do. But in bumpy IMC I might be chasing the TC and altimeter
indications all over the place. The 496 has a faster refresh that may
make this less of an issue.

On the other hand, the lag might keep me from overworking the controls
as I often do in IMC on a bumpy day. You won't correct for every little
deviation because the unit won't update that fast.

I like the idea of that little box that had solid state gyros in it and
you would velcro to the floor and hook up to a PDA. Instant electric
gyros without the gyro wear and tear. If only you could USB the signal
into the 396...

Good Luck,
Mike

I've been struggling with the same issue. I have a 396 but not a 430. I
also want more utility out of my airplane.

I finally said screw it..... I ordered the electric backup attitude
indicator from Sporty's. $1,871.45 with the AOPA discount. All of the
other options are not really usable. This way I have two indicators inches
apart that require no switching, batteries, cables, etc....


"Kelly" wrote in message
ups.com...
I would be interested in getting opinions about backup systems for a
vacuum pump failure and/or AI failure. I have a 172P with a single
vacuum pump system, standard instruments otherwise, and a Garmin 430.
I am most concerned about having a good backup if I lose a vacuum pump
or AI in IMC. I have been thinking about either a Garmin 396/496 or
the electric AI available from Sporty's. Looks like I could get a 396
or installed electric AI for about the same price ($2200 or so). While
I haven't seen the panel page/"6-pack" page on the 396 or 496, I have
read (in Aviation Consumer) that it's good enough to keep control of
the airplane in an emergency situation. Obviously, the 396/496 has a
number of other neat features such as inflight weather, terrain info,
etc. Any suggestions on which way to go with this.

BTW, I had also considered the Precise Flight backup vacuum system for
a while, and it certainly is cheaper (around $700 installed). However,
I was concerned by the fact that it would do nothing for you in the
event of failure of the AI vs. the primary vacuum pump.

Thanks.
Kelly