Sender: <marv@lancaironline.net> (Marvin Kaye)
To: lml
Date: Fri, 31 May 2002 16:34:38 -0400
Message-ID: <redirect-1253076@logan.com>
From: RWolf99@aol.com
Subject: Re: Vacuum v all electric
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I thought I'd get a response to my position that the traditional vacuum AI & 
DG with an electric TC is good enough for me, and the list has not let me 
down....

Jeff, I have no issue with your claim that an all-electric gyro system 
eliminates gyro failures due to loss of vacuum.  I will go a step further and 
assert that, if properly implemented (and that's a key point), a redundant 
electric power system can be made far more reliable than a vacuum system, 
which we should all know will fail someday if not changed prophylactically 
beforehand.

My guesstimate for MTBF (mean time between failures) for the vacuum system is 
something around 500 hours, based on anecdotal information in the aviation 
publications.  I will point out that Airborne now has a wear indicator on 
their new vacuum pumps, although I don't know whether the dry vacuum pumps 
wear down or fracture for other reasons.  In any event, electrics should be 
more reliable IF properly implemented.

However, history has shown that the likelihood of crashing due to a vacuum 
failure is tiny compared to other causes, and that was my main point.  Here's 
another example -- how many people die in midairs?  Probably more than due to 
vacuum failures.  How many Lancairs have TCAS?  Not many.  Wouldn't you 
rather put your extra money and weight in a TCAS system than another battery 
and $1500-per-each gyros?  Statistically, that's the wiser choice (and no, I 
can't afford that either, but wish that I could).

My claim was only that loss of control due to vacuum failures represents a 
tiny fraction of the fatal accidents experienced in the 50 years or so since 
the configuration became a de facto standard.  Further, my supposition is 
that the real problem is not noticing that the vacuum is gone until you're in 
an unusual attitude, and that most of us have the skills to fly partial panel 
IF we are warned that the vacuum is gone and we cover up the AI and DG before 
they spin down (hence the warning system I'm installing).

I recognize that my choice is not the right one for everyone, and actually 
would prefer that the antediluvian vacuum system would disappear.  Too bad I 
just can't afford it.  That doesn't mean that my airplane shouldn't ever poke 
it's nose into a cloud, though.

Thanks for your comments, on this and other issues.

- Rob Wolf