X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Fri, 20 Jan 2012 08:06:02 -0500 Message-ID: X-Original-Return-Path: Received: from nm10-vm1.bullet.mail.ne1.yahoo.com ([98.138.91.75] verified) by logan.com (CommuniGate Pro SMTP 5.4.3) with SMTP id 5356949 for lml@lancaironline.net; Thu, 19 Jan 2012 17:53:10 -0500 Received-SPF: none receiver=logan.com; client-ip=98.138.91.75; envelope-from=casey.gary@yahoo.com Received: from [98.138.90.55] by nm10.bullet.mail.ne1.yahoo.com with NNFMP; 19 Jan 2012 22:52:33 -0000 Received: from [98.138.226.161] by tm8.bullet.mail.ne1.yahoo.com with NNFMP; 19 Jan 2012 22:52:33 -0000 Received: from [127.0.0.1] by omp1062.mail.ne1.yahoo.com with NNFMP; 19 Jan 2012 22:52:33 -0000 X-Yahoo-Newman-Property: ymail-3 X-Yahoo-Newman-Id: 494387.57077.bm@omp1062.mail.ne1.yahoo.com Received: (qmail 76163 invoked by uid 60001); 19 Jan 2012 22:52:33 -0000 DomainKey-Signature:a=rsa-sha1; q=dns; c=nofws; s=s1024; d=yahoo.com; h=X-YMail-OSG:Received:X-Mailer:References:Message-ID:Date:From:Reply-To:Subject:To:In-Reply-To:MIME-Version:Content-Type; b=VRXs7QqSOYAvGvncWHFhrawtDW/P4lJjWWQPf233fRryqwfzI/wqFdw44bu50MMPg4G072yx9ZNHLdLfHUW6TbqndJdzAXdm/e4eTIwU+7ViL+JeZa1qlIwXtxeXQk3JjnF/3UnVW35hgG1xBUhIvsS+z3sQURqra3zasK4i45c=; X-YMail-OSG: g.BW4rMVM1m9cOEHxm2Hv1Rmb3uIwiSTg73OpF6t0ijQIMP JNYMIW9dw Received: from [97.122.177.194] by web125603.mail.ne1.yahoo.com via HTTP; Thu, 19 Jan 2012 14:52:33 PST X-Mailer: YahooMailWebService/0.8.115.331698 References: X-Original-Message-ID: <1327013553.57287.YahooMailNeo@web125603.mail.ne1.yahoo.com> X-Original-Date: Thu, 19 Jan 2012 14:52:33 -0800 (PST) From: Gary Casey Reply-To: Gary Casey Subject: Re: Steam Gauge Backup X-Original-To: Lancair Mailing List In-Reply-To: MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="933233344-1114805286-1327013553=:57287" --933233344-1114805286-1327013553=:57287 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: quoted-printable Just a quick comment on the redundancy issue. =A0I read the comment that a = vacuum system is not a good candidate for a back-up because of the known po= or durability of most vacuum pumps. =A0But that doesn't by itself reduce re= liability. =A0What happens if one has two electronic systems and both get d= isabled by a lightning strike? =A0Say there is a one in a million chance of= getting struck by lightning and there is a 1 in 2 chance that both systems= will be disabled. =A0That says that there is a 1 in 2 million chance that = you will have a really bad rest-of-the-day. =A0Now put in a vacuum system t= hat will absolutely not fail as a result of a lightning strike. =A0There is= , say, a MBTF of 500 hours for the vacuum pump(I think it is more like 1,00= 0 hours). =A0It will take maybe 30 minutes to get on the ground after the l= ightning strike takes out all the electronics. =A0What is the odds of the v= acuum system failing in that 30 minutes? =A0Presumably 1 in 1,000. =A0So th= e odds of the electronic system failing AND the vacuum system failing in the= next 30 minutes is 1 in a million times 1 in a thousand, or 1 in a billion= . =A0You only need the vacuum system to keep working for the time it takes = you to get to the ground.=0A=0ASo the all-electronic system will have a 1 i= n 2 million chances of killing you, while the combination of an electronic = primary and the not-as-reliable vacuum system has a 1 in a billion chance o= f killing you. =A0500 times better than the all-electronic system.=0A=0ATha= t's why I have an engine-driven vacuum pump and a vacuum AI in mine, along = with the electronic EFIS.=0AGary Casey --933233344-1114805286-1327013553=:57287 Content-Type: text/html; charset=iso-8859-1 Content-Transfer-Encoding: quoted-printable
Just a quick c= omment on the redundancy issue.  I read the comment that a vacuum syst= em is not a good candidate for a back-up because of the known poor durabili= ty of most vacuum pumps.  But that doesn't by itself reduce reliabilit= y.  What happens if one has two electronic systems and both get disabl= ed by a lightning strike?  Say there is a one in a million chance of g= etting struck by lightning and there is a 1 in 2 chance that both systems w= ill be disabled.  That says that there is a 1 in 2 million chance that= you will have a really bad rest-of-the-day.  Now put in a vacuum syst= em that will absolutely not fail as a result of a lightning strike.  T= here is, say, a MBTF of 500 hours for the vacuum pump(I think it is more li= ke 1,000 hours).  It will take maybe 30 minutes to get on the ground after the lightning strike takes out all the electronics.  Wha= t is the odds of the vacuum system failing in that 30 minutes?  Presum= ably 1 in 1,000.  So the odds of the electronic system failing AND the= vacuum system failing in the next 30 minutes is 1 in a million times 1 in = a thousand, or 1 in a billion.  You only need the vacuum system to kee= p working for the time it takes you to get to the ground.

So the all-electronic system will have a 1 in 2 million chances of = killing you, while the combination of an electronic primary and the not-as-= reliable vacuum system has a 1 in a billion chance of killing you.  50= 0 times better than the all-electronic system.

Tha= t's why I have an engine-driven vacuum pump and a vacuum AI in mine, along = with the electronic EFIS.
Gary Casey
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