The International Civil Aviation Organisation (ICAO) is preparing an amendment to Annex 13 (Amendment 17), which will change the definition of serious incidents.
Annex 13 contains the international Standards and Recommended Practices for aircraft accident and incident investigation. It provides a better understanding of accidents/incidents, helps to identify hazards, conduct risk assessments and makes recommendations on how to manage risks and communicate findings.
So what will Amendment 17 bring?

The change will affect the definition of a serious incident. At present, the severity of an event is based on the proximity of an occurrence to an accident outcome. If an occurrence results in a severe undesirable outcome (e.g. aircraft hull loss or loss of life), it is classified as an accident. If the accident is prevented or did not occur due to luck or providence, the incident is considered as a serious incident.

Amendment 17 considers the barriers in place to prevent the event from happening or reduce the impact of it if it does. If the barriers prevent an accident outcome, then the event will not be classified as a serious incident, but instead, as an incident. If all the barriers fail, but the accident is prevented by luck or providence, the occurrence will be classified as a serious incident under Amendment 17.

What is a barrier?

A barrier is a safety measure or layer of protection that exists to either reduce or eliminate the likelihood of an undesirable event occurring or mitigating the impact of the event should it occur. Barriers can be anything from procedures, systems, or equipment that can be linked with a particular threat or outcome. For example, Traffic Collision Avoidance System (TCAS) is a barrier to reduce the likelihood of two large commercial aircraft operating in close proximity to one another.

A wider perspective to occurrence reporting

The new amendment will bring a wider perspective to occurrence reporting and will recommend evaluating the effectiveness of barriers when assessing occurrences. It will also create an opportunity for the industry to consider barriers and their respective effectiveness when reviewing/investigating occurrences and exploring corrective actions.

Barrier Modelling in Aviation

If you are unsure what the upcoming changes will mean for you and your organisation, we have introduced a one-day training course, Barrier Modelling in Aviation, preparing delegates for the amendment to ICAO Annex 13. The course will provide delegates with an understanding of the concept of barrier modelling as referenced in the Amendment 17 and will give an overview of different barrier modelling techniques and how these models can be used to create meaningful Safety Performance Indicators (SPIs).

Get in touch

For more information and advice about the changes to ICAO Annex 13, please email

For details on our Barrier Modelling Training Course, please contact our training team: +44 (0) 330 0224401;

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