In order to further integrate your day to day management activities with risk management
strategies consider using additional capabilities of the bowtie.
As the aviation industry moves further towards ‘performance based’ safety management, it is
increasingly desirable to define the existing acceptable level of safety and monitor changes in
performance using a range of Safety Performance Indicators SPIs.
Further information on SPIs (activity and outcome) is available if you access the Significant
Seven bowtie templates.
By identifying safety controls, the bowtie provides a framework for targeting data collection.
It also provides a means of demonstrating the real world effectiveness of the controls and on how
risk is being managed. This can be achieved through the creation of Safety Performance Indicators
(SPIs) and example SPIs relevant to the Significant Seven templates are available for your
Measuring safety performance is a key activity of an effective safety management system (SMS).
The BowTie barrier modelling process enables the identification of the controls that are in place
to manage risks. The objective of SPIs is to measure how effective these controls are at preventing
undesirable safety outcomes. They are also used to identify trends in performance relative to an
organisation’s safety objectives, allowing action to take place to address undesirable changes.
There are broadly two types of SPIs:
In order to appreciate the effectiveness of a control in preventing or mitigating the impact of
a particular type of undesirable event (such as the use of standardised radiotelephony to prevent
runway incursions), it is useful to monitor and measure effectiveness using a combination of
activity and outcome indicators.
Often referred to as leading indicators, an activity indicator is a measure of whether or not a
control is actually in place. Activity indicators require a routine systematic check that key
activities are undertaken as intended. It can be inferred then that these indicators are designed
to assess the positive inputs into a safety system. They are proactive measures and often measure
performance against a level of tolerance for a particular event type. Thus, these indicators
highlight the need for action when a tolerance level is exceeded.
Often referred to as lagging indicators, an outcome indicator is a measurement of events after
they have occurred. In the context of safety, these are almost always considered to be undesirable
events. These indicators can inform an organisation as to the effectiveness of the controls in
place. They are, by their very nature, reactive indicators.
Generally, outcome indicators can fall into three categories:
The above information on Safety Performance Indicators has been developed from guidance provided
to the UK rail industry by RSSB (Rail Safety & Standards
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