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Date: Fri, 20 Jan 2012 12:42:12 -0500
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From: Dave Saylor <dave.saylor.aircrafters@gmail.com>
Subject: Re: [LML] Re: Steam Gauge Backup
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Andres, I've had your melted lens on display in my office for a while
now.  Let me know if you'd like it back.  It's a great conversation
piece!

Dave Saylor
AirCrafters
140 Aviation Way
Watsonville, CA 95076
831-722-9141 Shop
831-750-0284 Cell


On Fri, Jan 20, 2012 at 6:42 AM, Andres Katz <bu131@swbell.net> wrote:
> I have been struck while flying twice, once it melted the lens on the iv-=
p
> and blew open the wing extension, the second time in a 737 landing in dfw=
,
> Once in a million? I guess I am unlucky
>
> Sent from my iPad
>
> On Jan 20, 2012, at 7:06 AM, Gary Casey <casey.gary@yahoo.com> wrote:
>
> Just a quick comment on the redundancy issue. =C2=A0I read the comment th=
at a
> vacuum system is not a good candidate for a back-up because of the known
> poor durability of most vacuum pumps. =C2=A0But that doesn't by itself re=
duce
> reliability. =C2=A0What happens if one has two electronic systems and bot=
h get
> disabled by a lightning strike? =C2=A0Say there is a one in a million cha=
nce of
> getting struck by lightning and there is a 1 in 2 chance that both system=
s
> will be disabled. =C2=A0That says that there is a 1 in 2 million chance t=
hat you
> will have a really bad rest-of-the-day. =C2=A0Now put in a vacuum system =
that
> will absolutely not fail as a result of a lightning strike. =C2=A0There i=
s, say,
> a MBTF of 500 hours for the vacuum pump(I think it is more like 1,000
> hours). =C2=A0It will take maybe 30 minutes to get on the ground after th=
e
> lightning strike takes out all the electronics. =C2=A0What is the odds of=
 the
> vacuum system failing in that 30 minutes? =C2=A0Presumably 1 in 1,000. =
=C2=A0So the
> odds of the electronic system failing AND the vacuum system failing in th=
e
> next 30 minutes is 1 in a million times 1 in a thousand, or 1 in a billio=
n.
> =C2=A0You only need the vacuum system to keep working for the time it tak=
es you
> to get to the ground.
>
> So the all-electronic system will have a 1 in 2 million chances of killin=
g
> you, while the combination of an electronic primary and the not-as-reliab=
le
> vacuum system has a 1 in a billion chance of killing you. =C2=A0500 times=
 better
> than the all-electronic system.
>
> That's why I have an engine-driven vacuum pump and a vacuum AI in mine,
> along with the electronic EFIS.
> Gary Casey