Can vacuum AI be removed if a certified electric one is installed??

[Dave]

I had an interesting discussion with other pilots about converting my
Piper Cherokee 6 to all electric. This would basically require
replacing the AI and DG with electric AI and elec. HSI. So, then,
there would be no use for vacuum pump. But, one pilot said that the
certified elec. AI only allows for installation of the unit, and that
the FAA would *NOT* approve full removal of the vacuum instrument if
it was delivered and certified with the aircraft. Any experiences on
this?

My goal would be to put an elec. AI and HSI in the panel, dump the two
vacuum guages and also dump the vacuum pump (some weight savings!).
Has anyone done this successfully?

[Newps]

Dave wrote:
> I had an interesting discussion with other pilots about converting my
> Piper Cherokee 6 to all electric. This would basically require
> replacing the AI and DG with electric AI and elec. HSI. So, then,
> there would be no use for vacuum pump. But, one pilot said that the
> certified elec. AI only allows for installation of the unit, and that
> the FAA would *NOT* approve full removal of the vacuum instrument if
> it was delivered and certified with the aircraft. Any experiences on
> this?
>
> My goal would be to put an elec. AI and HSI in the panel, dump the two
> vacuum guages and also dump the vacuum pump (some weight savings!).
> Has anyone done this successfully?

Talked to my avionics shop about an electric AI, the ones you see for
$1800 from RC Allen. They have to send about 90% of them back because
they fail in less than 100 hours. He says if you want one you can
depend on you're looking at $4K.

[Bill]

> Dave wrote:
> > I had an interesting discussion with other pilots about converting my
> > Piper Cherokee 6 to all electric. This would basically require
> > replacing the AI and DG with electric AI and elec. HSI. So, then,
> > there would be no use for vacuum pump. But, one pilot said that the
> > certified elec. AI only allows for installation of the unit, and that
> > the FAA would *NOT* approve full removal of the vacuum instrument if
> > it was delivered and certified with the aircraft. Any experiences on
> > this?
> >
> > My goal would be to put an elec. AI and HSI in the panel, dump the two
> > vacuum guages and also dump the vacuum pump (some weight savings!).
> > Has anyone done this successfully?
>
> Talked to my avionics shop about an electric AI, the ones you see for
> $1800 from RC Allen. They have to send about 90% of them back because
> they fail in less than 100 hours. He says if you want one you can
> depend on you're looking at $4K.
>

That is total BS. Find another avionics shop.

[Bill]

> I had an interesting discussion with other pilots about converting my
> Piper Cherokee 6 to all electric. This would basically require
> replacing the AI and DG with electric AI and elec. HSI. So, then,
> there would be no use for vacuum pump. But, one pilot said that the
> certified elec. AI only allows for installation of the unit, and that
> the FAA would *NOT* approve full removal of the vacuum instrument if
> it was delivered and certified with the aircraft. Any experiences on
> this?
>
> My goal would be to put an elec. AI and HSI in the panel, dump the two
> vacuum guages and also dump the vacuum pump (some weight savings!).
> Has anyone done this successfully?

Aircraft manufacturers are doing it, but only with some redundancy in the
electrical system.

Call your FSDO and ask them if they would approve it on a 337 as a matter of
equivalent level of safety or better.

Make sure that after the modification you can fly for min 30 minutes on the
battery using essential equipment. The new electric AI and HSI will be part
of that essential equipment. You'll need to find out from your battery
manufacturer what the Amp-Hour rating is at 30 minute and 60 minute
discharge rates. Add up all your essential loads for night IFR and see if
it fits. Consider putting a larger capacity battery and in general sprucing
up your electrical system cables, terminals, etc where anything is wearing
out.

Take a look at what Diamond Aircraft does with their DA-40. It's got a
emergency battery pack full of a bunch of alkaline C cells hidden under the
panel. If you lose your alternator, you get power to everything from the
main battery. If the main battery dies, you flip the emergency battery
switch and the attitude indicator and some panel lights are run off this
emergency battery pack for another hour or more. Relatively inexpensive
compared to the cost of a new electric AI and HSI and would help you get it
approved. Batteries in the pack are automatically replaced at annual.

[Fast Eddy]

I would recommend the Dynon Development EFIS instead. Not certified, FAA
has 50 reasons why you can't use it in a certificated A/C but it
replaces all 5 primary instruments and adds 5 additional functions.
BTW. It works perfectly!



Dave wrote:
> I had an interesting discussion with other pilots about converting my
> Piper Cherokee 6 to all electric. This would basically require
> replacing the AI and DG with electric AI and elec. HSI. So, then,
> there would be no use for vacuum pump. But, one pilot said that the
> certified elec. AI only allows for installation of the unit, and that
> the FAA would *NOT* approve full removal of the vacuum instrument if
> it was delivered and certified with the aircraft. Any experiences on
> this?
>
> My goal would be to put an elec. AI and HSI in the panel, dump the two
> vacuum guages and also dump the vacuum pump (some weight savings!).
> Has anyone done this successfully?

[Stu Gotts]

On Fri, 09 Jan 2004 19:17:43 GMT, "Bill" > wrote:

>> Dave wrote:
>> > I had an interesting discussion with other pilots about converting my
>> > Piper Cherokee 6 to all electric. This would basically require
>> > replacing the AI and DG with electric AI and elec. HSI. So, then,
>> > there would be no use for vacuum pump. But, one pilot said that the
>> > certified elec. AI only allows for installation of the unit, and that
>> > the FAA would *NOT* approve full removal of the vacuum instrument if
>> > it was delivered and certified with the aircraft. Any experiences on
>> > this?
>> >
>> > My goal would be to put an elec. AI and HSI in the panel, dump the two
>> > vacuum guages and also dump the vacuum pump (some weight savings!).
>> > Has anyone done this successfully?
>>
>> Talked to my avionics shop about an electric AI, the ones you see for
>> $1800 from RC Allen. They have to send about 90% of them back because
>> they fail in less than 100 hours. He says if you want one you can
>> depend on you're looking at $4K.
>>
>
>That is total BS. Find another avionics shop.

Shouldn't say that unless you know which part of the country he's in.
Here in the southwest, the new instruments will last about 2 years on
the average, before the cheap **** plastics they use inside them start
to fail. If you want a good instrument, try getting an older one
that's been serviced by a good o/h shop.
>

[Nathan Young]

(Dave) wrote in message >...
> I had an interesting discussion with other pilots about converting my
> Piper Cherokee 6 to all electric. This would basically require
> replacing the AI and DG with electric AI and elec. HSI. So, then,
> there would be no use for vacuum pump. But, one pilot said that the
> certified elec. AI only allows for installation of the unit, and that
> the FAA would *NOT* approve full removal of the vacuum instrument if
> it was delivered and certified with the aircraft. Any experiences on
> this?
>
> My goal would be to put an elec. AI and HSI in the panel, dump the two
> vacuum guages and also dump the vacuum pump (some weight savings!).
> Has anyone done this successfully?


I like the idea of adding an elec AI to the panel, but until you can
add dual alternators and a split bus to your plane, I would not remove
the vacuum one, nor do I think the FAA would allow you to remove the
vacuum gyro.

Electrical failures are pretty common in light singles. In my
opinion, the charging system is crap, with multiple points of failure:
alternator, alternator belt, voltage regulator, overvoltage regulator,
circuit breaker, field current switch plus all the wiring to
interconnect these. Lose any element of the charging circuit, and the
entire thing fails (sometimes destructively), leaving only the battery
to power the bus.

I like the split/dual bus designs on the newer planes - and this (I
think) is what the FAA is requiring to go with a full electric panel.

Mid-Continent makes an electric AI with integrated battery. The
battery will keep the gyro turning for 1 hr after an electrical
failure. Cool idea, but it is pricey. Book price is $4450
http://www.mcico.com/pdf/4300.pdf

-Nathan

[[email protected]]

On 10-Jan-2004, (Nathan Young) wrote:

> I like the idea of adding an elec AI to the panel, but until you can
> add dual alternators and a split bus to your plane, I would not remove
> the vacuum one, nor do I think the FAA would allow you to remove the
> vacuum gyro.


I fully agree with this . At most, the complete vacuum system, including
gyros, costs just a few pounds and provides full redundancy in case of
electric failure or failure of any one instrument. Why get rid of it?

We have a backup electric AI in our Arrow, and I consider it virtually
essential for safe IFR operations. BTW, a good backup for the vacuum DG is
the HSI function on a yoke-mounted GPS.

--
-Elliott Drucker

[G.R. Patterson III]

Dave wrote:
>
> I had an interesting discussion with other pilots about converting my
> Piper Cherokee 6 to all electric. This would basically require
> replacing the AI and DG with electric AI and elec. HSI. So, then,
> there would be no use for vacuum pump. But, one pilot said that the
> certified elec. AI only allows for installation of the unit, and that
> the FAA would *NOT* approve full removal of the vacuum instrument if
> it was delivered and certified with the aircraft.

The key word in that last sentence is *if*. My Maule, for example, is certified
with no vacuum instruments at all. The vacuum system is listed as optional in the
owner's manual; in fact, I originally bought the plane with no system or instruments
installed.

I have not checked to see if electrical instruments are also listed as optional
equipment for the plane. If they are, I could replace my vacuum system with
electrical alternatives under the aircraft certificate. If not, I could still
replace the system, but there would be a significant amount of paperwork.

So, check the owner's manual for the Cherokee. If the plane was certified with
a vacuum system being optional, then it can be removed.

George Patterson
Great discoveries are not announced with "Eureka!". What's usually said is
"Hummmmm... That's interesting...."

[Michael]

(Dave) wrote
> My goal would be to put an elec. AI and HSI in the panel, dump the two
> vacuum guages and also dump the vacuum pump (some weight savings!).
> Has anyone done this successfully?

Depends on what you mean by successfully. I know people who have done
it. I consider their installations to be adequate for day-VFR only.
However, the FAA does not concur.

First off, you're getting a lot of bad info here. There is NO
requirement for redundancy for IFR under Part 91. It's perfectly
legal (though not too smart) to have all three required gyros powered
from the same non-redundant source. In fact, it used to be pretty
common to have airplanes that were IFR certified equipped with all
three gyros driven by vacuum. The TriPacers with the advanced panel
actually came that way from the factory.

Second, it's a very rare light airplane that is certified with any
gyros at all as required equipment. Ditto the vacuum pump. On most
of the GA fleet, it's perfectly legal to remove ALL the gyros AND the
vacuum pump and not replace them at all. Only thing is, you can't fly
IFR that way - but that's a part 91 requirement, not a maintenance
issue.

However, just because something is legal does not mean it won't cause
you grief - especially something as dumb as making all your gyros
electric and driven by a single electrical bus. The way to make this
happen is to submit two Form 337's, a couple of weeks apart and under
separate cover.

The first form would list the removal of the existing gyros and the
installation of the new gyros by model number. The second form would
list the removal of the vacuum gauges and vacuum pump, and the
installation of a cover plate over the accessory pad. Either one by
itself will raise no eyebrows, but combining everything can cause some
fed who doesn't actually know the rules but thinks he does (much like
some people who posted here) to make your life difficult.

Good luck, and I hope your master contactor doesn't decide to go TU in
IMC.

Michael

[Bill]

> First off, you're getting a lot of bad info here. There is NO
> requirement for redundancy for IFR under Part 91. It's perfectly
> legal (though not too smart) to have all three required gyros powered
> from the same non-redundant source. In fact, it used to be pretty
> common to have airplanes that were IFR certified equipped with all
> three gyros driven by vacuum. The TriPacers with the advanced panel
> actually came that way from the factory.
>

Don't forget that there are operational FARs like you quote and
airworthiness FARs. For example, if the instruments are converted to all
electric, then look at 23.1331 Instruments Using A Power Source - For each
instrument that uses a power source, the following apply: (c) There must be
at least two independent sources of power ... and a manual or automatic
means to select each power source.

The original poster's airplane is certificated under CAR3 and not FAR23 and
so 21.101 could be applicable if this modification was performed by STC.

[Michael]

"Bill" > wrote
> Don't forget that there are operational FARs like you quote and
> airworthiness FARs. For example, if the instruments are converted to all
> electric, then look at 23.1331 Instruments Using A Power Source - For each
> instrument that uses a power source, the following apply: (c) There must be
> at least two independent sources of power ... and a manual or automatic
> means to select each power source.
>
> The original poster's airplane is certificated under CAR3 and not FAR23 and
> so 21.101 could be applicable if this modification was performed by STC.

However, no STC is required to perform the modification, so 21.101 is
inapplicable. 23.1331 is also inapplicable, and you will note that
most airplanes currently in service do not meet it.

In other words, none of this means anything.

Michael