Bow-tie method is a tool which visualises the causes (threats) and effects (consequences) of serious events (accidents/ incidents). It is extremely helpful for cases of potentially disastrous results, which are very rare and enough data are not available. Bow-tie is an advancement of the James Reason Swiss Cheese Model, further showing the barriers and the controls of a system.
The visualisation creates a bow-ties shape (and thus the name). The centre of it, is the main event (e.g. runway excursion). On the left side we place the threats that left uncontrolled could give the result, but the proactive extension is to also place the controls we have in place (or can put in place) to prevent this. On the right side we have the potential consequences of the event, but likewise, we have the recovery controls (reactively) that would mitigate or minimise the effect of the consequences.
It is a graphical display of all the action, procedures, processes that help the organisation control the operations. It provides a clear view for the managers about the required controls and identifies the key safety barriers.
Key Elements of Bow-tie:
- Hazard: anything with the potential to cause harm
- Threat: a possible cause that will potentially release the hazard
- Threat Control: any tools used like procedures, checklists, equipment etc
- Escalation Factors: Reasons why a control might be inefficient or defeated
- Escalation Factor Controls: further controls if initial control fail (fail operational systems)
- Event: the actual event (e.g. loss of control)
- Recovery measures: all measures that limit the potential consequences
- Consequence: the outcomes after the release of the hazard
- Mitigation Measure
Bow-tie methodology is excellent for supporting safety teams and audit teams in their investigations. It is a process that allows for direct feedback. They can be used for understanding policies and objectives, for performing safety risk management, as part of safety assurance and as means of promotion (both as training and communication).
The steps to create a bow-tie are:
- Select a leader and process owner
- Develop the initial scope of the process
- Examine threats and identify hazards
- Set the subject matter expert team
- Conduct the workshop
- Assign and link information on controls and escalation factors
- Review the work
- Communicate the results
The target is to create bow-ties for all the threats and then combine them into as few as possible. UK CAA has come up with the Significant Seven, which as per the data, are the 7 most usual top events of accidents (Controlled flight into Terrain-CFIT, Loss of Control – LOC, Runway Excursion, Runway Incursion, Ground Handling, Airborne Conflict and Fire). Many software is available in the market that can achieve the proper visualisation.