Severity of Effect

Severity refers to the impact of a failure mode on the end-effect nominated for the system model and is ranked in terms of the impact of failure on the system and mission.

For Risk Priority Numbers (RPN) the crisp severity scale is between 1 and 10. For Criticality Matrix, it is a ranking between 1 (most severe) and 4 (least severe).

Severity of Effect Ranking

Ranking	Category	Severity Class	Description
10	Catastrophic	I	Loss of mission and aircraft, injury to pilot.
7 - 9	Critical	II	Loss of mission, extensive repairs required.
4 - 6	Marginal	III	Degraded mission, significant repairs required.
2 - 3	Minor	IV	No effect on mission, some repairs/maintenance required.
1	Minor	IV	No effect on mission, minor repair/maintenance required.

Note: The Severity rankings are based on MIL-STD-1629A and express severity in terms of impact on aircraft availability, pilot and mission.

Assignable Rankings	Unassignable Rankings
Component Functional Failure Modes	Causes
Subsystem Functional Failure Modes	Mechanisms
System Functional Failure Modes	Faults
	Pair Functional Failure Modes

Note: Severity ranking assigned to failure mode responses (High, Low, Zero) will be reported when the element is the end-effect and a lower-level failure concept leads to this failure mode.

Assigning Severity of Effect Rankings

Assigning Severity rankings of End-Effect Failure Modes in a model are described in the steps below:

1. Open the Functions Editor (for System-level End Effects) or Failure Diagram for local item severity
2. Select an output flow property in the Functions Editor or failure concept on the Failure Diagram
3. Select the Criticality tab in the Properties View
4. Use the slider to change the severity value or enter a numerical value in the provided field