The CAA UK has excellent website pages explaining the use of Bowtie modelling to assist the identification and management of risk.
The following information is derived from these pages.
Bowtie models can provide:
- An effective, visual depiction of risk.
- A balanced risk overview for the whole aviation system between internal and external stakeholders.
- An increased awareness and understanding of the safety risk.
- The best practice guidance material for safety risk management at an operational and regulatory level.
- An identification of critical risk controls and an assessment of their effectiveness.
- An identification of SPIs to monitor performance of risk control.
Bowtie models work with a known Hazard, that may result in a Top Event, which is the release or loss of control of the hazard which results in an undesired state.
Consider driving on a highway; A Hazard may be a condition (eg icing), an object (eg another vehicle) or an activity (eg driving). The Top Event could be the loss of control of the car
The left side of the model shows the Threats to operations and preventative controls that may be implemented to prevent the Top Event occurring.
Continuing the example; a Threat could be a blown tyre. Preventative measures would be regular inspection, or skilled driver training if the Top Event becomes ‘live’ and occurs.
The right side of the model shows consequence, and recovery controls to reduce the likelihood, or reduce the severity, of the consequences of the top event being ‘live’.
Continuing the example; a consequence could be collision with another vehicle resulting in injury and damage. A reduction control could be advanced ABS to maintain control, a mitigating control could be airbags to reduce injury.
The model may also include escalation factors which are reasons as to why a control may not be defeated or less effective.
Continuing the example; an escalation factor could be an untrained driver who does not understand how to counter a tyre blow out. An obvious control against this is to seek out extra driver training.
In identifying safety risk priorities, what can also be labeled on the Bowtie is;
- Control effectiveness
- Control function and criticality
- Control ownership and type
- Threat exposure