Aero Advantage closing shop.

On Tue, 11 May 2004 03:59:27 GMT, "Richard Kaplan"
wrote:


"David Megginson" wrote in message
le.rogers.com...


It can be a fraction of that if you don't mind yet another portable device
cluttering your cockpit:

If we are talking about why airplanes have vacuum systems then we need to
keep the discussion to certified equipment -- other options may work but if
they are not certified then the FAA will require a vacuum system for legal
IFR.

system? As I mentioned earlier, I have not yet managed to find a single
example of a fatal accident caused by a vacuum-pump failure in a
fixed-gear
plane flying IFR. There must be one or two, but it does not appear to be
a
significant risk.

I think part of this may be related to how the accidents are classified.

For example, there are a number of examples each year of IFR airplanes which
simply suffer inflight break-up for unknown reasons; these could well be due
to vacuum pump failure.

What's the FAA position on venturi-driven instruments?

Don

Richard Kaplan wrote:

For example, there are a number of examples each year of IFR airplanes which
simply suffer inflight break-up for unknown reasons; these could well be due
to vacuum pump failure.

The pilot would have to not report the vacuum pump failure to ATC, and then
the wreckage would have to be so scattered or burned that the NTSB could not
check the vacuum pump in the wreckage to see if the shaft had sheared before
impact (something they always seem to do). It's not that it's impossible
that that's happened, but there no evidence that it's a significant pattern
for fixed-gear planes -- if there were more than a couple such cases, you'd
expect at least one where the wreckage wasn't burned or the pilot did report
the failure.

If I were investigating this question, I'd try to find some examples where a
fixed-gear plane experienced an inflight break-up flying IFR in IMC, it was
not possible for the NTSB to check the vacuum pump (say, because of a fire),
the radar and ATC voice tapes show the plane flying fine in IMC until just
before the crash, and there was no likely convective activity, icing, or
mountain wave activity in the area.


All the best,


David

Don Tuite wrote:

What's the FAA position on venturi-driven instruments?

Better be able to heat them.

George Patterson
If you don't tell lies, you never have to remember what you said.

It's curious that those who caution against the electronic substitutes want
dual alternators, dual (triple) batteries, dual DC bus, and more to run the
normally vacuum driven instruments. Curious because alternators, DC buses
and batteries rarely fail, and the single vacuum pump which is currently
allowed (required) are somewhat failure prone and rarely give any warning
before failure.

Electronics have clearly far outstripped mechanical instruments in terms of
performance and reliability. They can also be relatively inexpensive over
their lifetime, and are frequently able to give much more information. The
reason they are not in your aircraft relates solely with the cost of
certification and insurance.

This is one case where the caution of the regulating bodies may well be
holding safety advancements back.

Occom wrote:

It's curious that those who caution against the electronic substitutes want
dual alternators, dual (triple) batteries, dual DC bus, and more to run the
normally vacuum driven instruments. Curious because alternators, DC buses
and batteries rarely fail, and the single vacuum pump which is currently
allowed (required) are somewhat failure prone and rarely give any warning
before failure.

I think that the point having gyros with different power sources. The
vacuum pump, for good or ill, is entirely redundant to the electrical system
-- it's unlikely that both will fail on the same flight.

I agree that the vacuum pump fails more often than the alternator, but on
the other hand, alternators do fail fairly often as well -- I know several
pilots who've experienced that. Redundancy, whether vacuum/electric or dual
electric, is the only safe option.


All the best,


David

David Megginson wrote:
I agree that the vacuum pump fails more often than the alternator, but on
the other hand, alternators do fail fairly often as well -- I know several
pilots who've experienced that. Redundancy, whether vacuum/electric or dual
electric, is the only safe option.

There's no doubt that redundancy is critical. I suspect the trend in
the future will be towards dual (if not more) alternators. A typical GA
engine has three accessory pads on the back, generally filled with two
magnetos and a vacuum pump. We should get rid of all the crud, and
instead put three little alternators in their place. This would supply
triple-redundant power for electronic ignition, solid-state gyros,
fadec, etc. It would work better, weigh less, and be more reliable than
the 50 year old rube goldberg designs we're flying now.

Not likely I'll ever see it, but I can dream, can't I?

David Megginson wrote
Funny, you just listed my major purchases over the past six months: I bought
a Garmin 196 in December, and just ferried my plane back from Montreal this
afternoon with a (used but factory updated) WX-900 Stormscope installed by
an experienced shop. It was the perfect afternoon for it: solid IMC above
1,200 ft AGL, with a small risk of occasional embedded TCU and CB (normally,
I cancelled flights under those conditions).

All I can tell you is that you've made the right purchases. If you're
already taking regular recurrent training, still have money left over,
and have a burning desire to spent it to improve safety in your plane,
go ahead and get the backup vacuum or electric attitude gyro. Can't
hurt, might help.

It's all about priorities. You can keep spending money forever.

Michael

In article gers.com, David
Megginson writes:

Of course, these become less and less useful as you go down the list (I
wouldn't be much on my chances with just the magnetic compass), but in real
life, but how much redundancy do you need before you've overdesigned the
system? As I mentioned earlier, I have not yet managed to find a single
example of a fatal accident caused by a vacuum-pump failure in a fixed-gear
plane flying IFR. There must be one or two, but it does not appear to be a
significant risk.


I have need to use my Precise Flight backup vacuum only once but then it was
worth the price.

Chuck

Occom wrote:

It's curious that those who caution against the electronic substitutes want
dual alternators, dual (triple) batteries, dual DC bus, and more to run the
normally vacuum driven instruments.

That's because the vacuum instruments have an electric backup in the turn coordinator
or turn&bank. If you use electricity for all of your instruments, there is no backup
when the electrical system fails. The solution is to put in a backup electrical
system.

Perhaps it would be better to start using the vacuum system to drive the turn
coordinator and install electric AI and DGs?

George Patterson
If you don't tell lies, you never have to remember what you said.

David Megginson wrote:

I agree that the vacuum pump fails more often than the alternator, but on
the other hand, alternators do fail fairly often as well -- I know several
pilots who've experienced that.

Yep. I've got a bit over 500 hours on my plane. Lost the alternator near SHD on a run
to Tennessee a few years ago. The vacuum pump is still breathing fine. On the other
hand, nothing quit working when the alternator died except for the fuel gauges. You
don't have something like a battery to keep things going for a while in a vacuum
system.

George Patterson
If you don't tell lies, you never have to remember what you said.