Probability Calculation

When the FHA analysis is performed and each failure condition is linked to Fault Tree in order to get expected failure probability, you may initiate the calculation.

To calculate probability for selected failure condition (SSA/AFO mode):

1.	Select specific function.

2.	Select failure condition.

3.	Choose Calculate selected FTA from the pop-up menu. Result of the calculation will be displayed in SSA/AFO report and in failure conditions table on the screen.

To calculate probability for multiple failure conditions (SSA/AFO mode):

1.	Select specific function (top function to calculate all, specific function to calculate only FTAs linked to failure conditions of this function and nested child functions).

2.	Choose Recalculate Assessment Means from "Calculation" menu. Result of the calculation will be displayed in SSA/AFO report and in failure conditions table on the screen.

Probabilities comparison

Both screen and report will show expected probability per average mission hour (calculated using Fault Trees as described above) and also objective probability (some reports may show both "Safety Requirements Objective" and "Design Objective" probabilities) per average mission hour. If expected calculated probability is greater than objective probability RAM Commander will provide red color indication in that grid/report line.

The objective probabilities ("Safety Requirements Objective" and "Design Objective") are defined in Safety/FMECA libraries - "Safety Severity" library and "End Effects" library. See the next paragraphs for more information about the libraries.