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Subject: Reliability Question
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This is a question for Brent and Hamid, but it also addresses the recent thread on reliability and redundancy.

I have been recently educated on the FAA approach to reliability for certified airplanes, which can be simply summarized as a connection between the probability of failure and the resulting consequences.? For the aircraft I was working with, a "catastrophic" failure (results in loss of aircraft, loss of all life) needed to have a probability of 10e-9 (that's one in a billion).? A "major hazard" (damage to aircraft, loss of?a passenger) needed to have a probability of 10e-8.? Similarly, lower consequences were allowed to happen more frequently.? The key point here is that there was no failure that was prohibited -- even a wing falling off.? We just had to make it so unlikely that the risks were acceptably small.? Acceptable risks are lower for airliners, and higher for two-person propeller airplanes.

FWIW, this goal was accomplished by making systems -- not components -- more reliable by strategically adding redundancy where it improved systm reliability.

My question for Brent and Hamid is this -- given your comments that an EFIS has a finite probability of failure, what is that number?? What would it be for a certified EFIS (like a Chelton) and what would it be for a non-certified system (like a Dynon)?

What I am getting at here is a quantitative way of ensuring that our proposed flight display systems have a reliability equal to that on a certified aircraft.? For example, if a Chelton failure probability is one in a million, and a Dynon failure probability?is one in a thousand, and the power supplies are separate (Dynon internal battery backup), wouldn't a Chelton + Dynon give you a one in a billion probability of total failure?

By the way, I personally don't believe the failure probability numbers that the systems safety engineers come up with.? I believe that the actual rate of failure is significantly higher.? However, I *do* believe that using this methodology has given us a fleet of aircraft whose reliability we are comfortable with.

- Rob Wolf
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This is a question for Brent and Hamid, but it also addresses the recent thread on reliability and redundancy.<br>
<br>
I have been recently educated on the FAA approach to reliability for certified airplanes, which can be simply summarized as a connection between the probability of failure and the resulting consequences.&nbsp; For the aircraft I was working with, a "catastrophic" failure (results in loss of aircraft, loss of all life) needed to have a probability of 10e-9 (that's one in a billion).&nbsp; A "major hazard" (damage to aircraft, loss of&nbsp;a passenger) needed to have a probability of 10e-8.&nbsp; Similarly, lower consequences were allowed to happen more frequently.&nbsp; The key point here is that there was no failure that was prohibited -- even a wing falling off.&nbsp; We just had to make it so unlikely that the risks were acceptably small.&nbsp; Acceptable risks are lower for airliners, and higher for two-person propeller airplanes.<br>
<br>
FWIW, this goal was accomplished by making systems -- not components -- more reliable by strategically adding redundancy where it improved systm reliability.<br>
<br>
My question for Brent and Hamid is this -- given your comments that an EFIS has a finite probability of failure, what is that number?&nbsp; What would it be for a certified EFIS (like a Chelton) and what would it be for a non-certified system (like a Dynon)?<br>
<br>
What I am getting at here is a quantitative way of ensuring that our proposed flight display systems have a reliability equal to that on a certified aircraft.&nbsp; For example, if a Chelton failure probability is one in a million, and a Dynon failure probability&nbsp;is one in a thousand, and the power supplies are separate (Dynon internal battery backup), wouldn't a Chelton + Dynon give you a one in a billion probability of total failure?<br>
<br>
By the way, I personally don't believe the failure probability numbers that the systems safety engineers come up with.&nbsp; I believe that the actual rate of failure is significantly higher.&nbsp; However, I *do* believe that using this methodology has given us a fleet of aircraft whose reliability we are comfortable with.<br>
<br>
- Rob Wolf<div class="AOLPromoFooter">
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