Domein Techniek
ASSIGNMENT FAULT TREE ANALYSIS
1
Consider the Fault Tree as provided below. This FTA is the qualitative result from a system safety
assessment on a certain system function. A failure of this function would lead to a catastrophic event.
The manufacturers of the various aircraft systems have provided the following failure probabilities for
a one-hour flight:
FA = 1.10-8
FB = FC = 2,5.10-8
FD = FE = 3.10-6
FF = Fg= 1.10-9
a. Derive the minimum cut-set expression where A-G represents the failure modes with their
particular failure probabilities [9 points]
b. Assess the result from (a) using the requirements from CS 25.1309. To what extend does
this system comply with the requirements? Explain how and why it does comply, or explain
how and why it does not comply. [3 points]
c. Explain the definition of “catastrophic” according to the CS/AMC 25.1309 by providing one
relevant effect [1 point], the allowable qualitative probability [1 point] and the allowable
quantitative probability [1 point] [3 points]
a) Minimum cut-set:
ABCD + EBF + A+D+G =
EBF + A + G +D
If…
- …the minimum cut-set expression is correct: 9 points
- …the full expression of the top-event is correct, but no Boolean reduction is applied (or
incorrectly applied): 6 points
- …the basic expression is not correct, but it has been demonstrated that an AND-gate
results in a product of probabilities (2 points) and/or an OR-gate results in the sum of
probabilities (2 points)
b) The system does not comply (1 point). According to the assignment description a failure of
the system results in a catastrophic event. The maximum failure probability for
catastrophic events is 10-9 per flight hour. Using the given failure probabilities per hour
results in a resulting failure probability of 3.10-6 for this system, which is bigger than the 10-
1
ASSIGNMENT FAULT TREE ANALYSIS
1
Consider the Fault Tree as provided below. This FTA is the qualitative result from a system safety
assessment on a certain system function. A failure of this function would lead to a catastrophic event.
The manufacturers of the various aircraft systems have provided the following failure probabilities for
a one-hour flight:
FA = 1.10-8
FB = FC = 2,5.10-8
FD = FE = 3.10-6
FF = Fg= 1.10-9
a. Derive the minimum cut-set expression where A-G represents the failure modes with their
particular failure probabilities [9 points]
b. Assess the result from (a) using the requirements from CS 25.1309. To what extend does
this system comply with the requirements? Explain how and why it does comply, or explain
how and why it does not comply. [3 points]
c. Explain the definition of “catastrophic” according to the CS/AMC 25.1309 by providing one
relevant effect [1 point], the allowable qualitative probability [1 point] and the allowable
quantitative probability [1 point] [3 points]
a) Minimum cut-set:
ABCD + EBF + A+D+G =
EBF + A + G +D
If…
- …the minimum cut-set expression is correct: 9 points
- …the full expression of the top-event is correct, but no Boolean reduction is applied (or
incorrectly applied): 6 points
- …the basic expression is not correct, but it has been demonstrated that an AND-gate
results in a product of probabilities (2 points) and/or an OR-gate results in the sum of
probabilities (2 points)
b) The system does not comply (1 point). According to the assignment description a failure of
the system results in a catastrophic event. The maximum failure probability for
catastrophic events is 10-9 per flight hour. Using the given failure probabilities per hour
results in a resulting failure probability of 3.10-6 for this system, which is bigger than the 10-
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