backup for vacuum pump/attitude indicator failure

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

: 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.

The DG will still work though. In something like the 172 (or my Cherokee), that's a good chunk of the necessary gyro for IMC.

What about a non-TSO'd electric AI? Seems like one should be able to install one of those for backup purposes.

-Cory

--

************************************************** ***********************
* Cory Papenfuss, Ph.D., PPSEL-IA *
* Electrical Engineering *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

"Kelly" writes:

I would be interested in getting opinions about backup systems for a
vacuum pump failure and/or AI failure. I have a 172P [...]

Considering the nature of the 172, you likely don't engage in too much
heavy duty IMC, so backup equipment could be of the "help me land now"
kind rather than "help me fly for a few hours more" kind.

[...] 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. [...]

You should also consider the iQue3600a, which has essentially the same
aviation features as the 396, at half the price, and with ground-side
utility as PDA and car GPS. (The other backup technologies you
mentioned have no separate ground utility.)

In any case, you should test it out. Borrow someone's
296/396/496/iQue or other portable aviation GPS, set it up in your
cockpit, go under the hood and do some partial-panel with a mostly
covered-up instrument panel. An hour or two might suffice.


- FChE

I wouldn't bother with a backup vac system because its use is limited.
A backup pump won't cure a dead AI. I would buy the Sporty's backup AI.
For under $2K and next to no labor (just a couple power hookups ) you
get full, 100% AI redudency.

-Robert, CFII


Kelly wrote:
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

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

(Frank Ch. Eigler) wrote in
:

Considering the nature of the 172, you likely don't engage in too much
heavy duty IMC, so backup equipment could be of the "help me land now"
kind rather than "help me fly for a few hours more" kind.

Why would you say this based on a model of a plane?

Original poster sounded like an owner, not a renter looking to upgrade /
install backup redundancy.

I own a Sundowner (might as well say a 172 equivelant) and do hard IMC as
much as I can so I have been following this thread rather closely myself.

Just because it's a C172 doesn't mean the plane won't be flown in hard IFR
on a frequent basis unless of course it's not an IFR certified bird in
which that kinda plane shouldn't be anywhere near a cloud anyway.

Allen

Why not install a 4 inch Venturi on the side or the belly of the
aircraft ( 50 bucks aircraft spruce) then route to a selector valve
then you could switch between engine pump or venturi. This will drive
BOTH AI and the DG.

Or you could install the venturi to drive a back up CHEAP ( older type;
black face) Gyro Horiz. I am sure an instrument shop will sell you one
at a good price as every one wants a color faced type.

Now what about BACK UP electrical power thats CHEAP and portable!


I use one in my Airplane it provides 5 hours of FULL Avionics power !
It cost LESS than 30 bucks to make and all parts are from WAL - MART!


Hint: GARDEN TRACTOR

A Lieberma writes:

(Hm, I am talking to myself. :-)

Considering the nature of the 172, you likely don't engage in too much
heavy duty IMC, so backup equipment could be of the "help me land now"
kind rather than "help me fly for a few hours more" kind.

Why would you say this based on a model of a plane? [...] Just
because it's a C172 doesn't mean the plane won't be flown in hard
IFR on a frequent basis [...]

The inherent limitations of range and speed complicate bad weather
diversion planning, power limits altitude reach and icing risk
exposure, small amount of redundancy turns malfunctions into
emergencies. So sure, it can be flown in hard IFR on a frequent
basis, but such greater risks have to be accepted.

- FChE

Hint, unless a homebuilt, all parts must be approved parts.


My vote for safety and redundancy would be for the Sporty's
AI [not as a replacement for T&B] and the 496 GPS. The 496
is aviation, marine and highway, it is your XM radio too.

Unlike the emergency attitude indicators used in jets, the
Sporty's AI does not have a separate battery for power.
You can have your shop create a redundant power source with
a small battery that will be charged from the bus, but
isolated if the alternator fails.



"wise purchaser" wrote in message
ps.com...
|
|
| Why not install a 4 inch Venturi on the side or the belly
of the
| aircraft ( 50 bucks aircraft spruce) then route to a
selector valve
| then you could switch between engine pump or venturi.
This will drive
| BOTH AI and the DG.
|
| Or you could install the venturi to drive a back up CHEAP
( older type;
| black face) Gyro Horiz. I am sure an instrument shop will
sell you one
| at a good price as every one wants a color faced type.
|
| Now what about BACK UP electrical power thats CHEAP and
portable!
|
|
| I use one in my Airplane it provides 5 hours of FULL
Avionics power !
| It cost LESS than 30 bucks to make and all parts are from
WAL - MART!
|
|
| Hint: GARDEN TRACTOR
|

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....