[SystemSafety] Difference between software reliability and astrology

[Prof. Dr. Peter Bernard Ladkin]

On 2024-08-22 01:26 , Derek M Jones wrote:
>
> To me 6-10 years is not Extremely improbable.

"Extremely improbable" is a technical term.

The definition is to be found in FAA AC 120-1309-1A Paragraph 9 Qualitative Assessment

[begin quote]

e. Qualitative Probability Terms

(1) Probable failure conditions are those anticipated to occur one or more times during the entire 
operational life of each airplane.

(2) Improbable failure conditions are those not anticipated to occur during the entire operational 
life of a single random airplane. However, they may occur occasionally during the entire operational 
life of all airplanes of one type.

(3) Extremely improbable failure conditions are those so unlikely that they are not anticipated to 
occur during the entire operational life of all airplanes of one type.

[end quote]

Paragraph 10. Quantitative Assessment

b. Quantitative Probability Terms

[begin quote]

(1) Probable failure conditions are those having a probability greater than on the order of 1 x 10^(-5).

(1) Improbable failure conditions are those having a probability greater than on the order of 1 x 
10^(-7) or less, but greater than on the order of 1 x 10^(-9).

(1) Extremely improbable failure conditions are those having a probability greater than on the order 
of 1 x 10^(-9) or less.

[PBL note: parentheses around the exponent have been added; in the original there are no parentheses]

[end quote]

EASA AMC 15.1309 is similar.

PBL

Prof. i.R. Dr. Peter Bernard Ladkin, Bielefeld, Germany
www.rvs-bi.de