Add Events and Gates

Build the fault tree with blank or imported events and AND or OR gates.

Use the fault-tree tools

The diagram palette contains these tools:

Tool	Purpose
New Event (Blank)	Create an event without an existing failure-element reference.
New Event (Import)	Import an existing failure element as an event.
New AND Gate / New OR Gate	Add a logic gate.
New Transfer Gate	Reference an existing FTA node.
Collapse/Expand Tree	Collapse or expand tree nodes.

You can select a tool from the palette on the right or select a parent gate and use the contextual tool bar that appears beside it.

Create a blank event

1. In the palette, select Tools > New Event (Blank).
2. Drop the event on the required parent gate.
3. Double-click the event.
4. In Properties, enter its Label, Name, and Summary.

5. Use one of the following input methods:

   • Enter the failure rate per hour and select an event exposure time in hours. ATICA calculates the probability automatically.
   • Enter a failure probability manually.

6. Select Finish.

Note

When failure rate and exposure time are set, ATICA calculates probability automatically. To fix a probability manually, first remove the exposure time or set the failure rate to zero.

Reuse exposure times

An exposure-time artifact must first be created for a single event. It cannot be created directly under an ATICA package.

To reuse an exposure time:

1. Create or select the event that will initially own the exposure time.
2. Open the event's Properties.
3. Use the pencil icon beside the event exposure-time field to create one exposure-time artifact.
4. Enter the exposure time in hours and finish editing the event.
5. Move the newly created exposure-time artifact from the event to the corresponding ATICA package.
6. In each additional event, select the existing exposure-time artifact from that package.

Note

Create the exposure-time artifact on an event before moving it. Creating it directly under an ATICA package is not supported.

Reference an existing failure element

An event without a failure-element reference is represented as an undeveloped event. Adding a reference converts it to a basic event.

The referenced failure element can come from a different architecture layer than the fault-tree top event. For example, a tree for a System Analysis failure condition can use a Logical Architecture functional failure or a Physical Architecture failure mode as a base event.

Create, then referenceImport directly

1. Create a New Event (Blank) on the required gate.
2. Open its Properties.
3. Under Basic Event > Failure Event, select the three-dot button.
4. Select the required failure element.
5. Set any required exposure time and select Finish.

1. Select New Event (Import).
2. In the transfer dialog, select the failure element and select OK.
3. In Properties, assign an exposure time if probability must be computed.

Warning

Referencing a failure element replaces the event's label and name. Its existing failure rate appears automatically when available. A manually entered rate overrides that value and may also override a future value from the referenced element.

Create a gate

1. From the tool box, select New AND Gate or New OR Gate.
2. Drop it on the required parent gate.
3. Double-click the gate.
4. Set its Label, Name, Summary, and Logic Type.
5. Select Finish.

Note

Changing Logic Type in Properties can shrink the gate symbol. Resize the symbol manually if this occurs.