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UK Civil Aviation Regulations

These are published by the CAA on our UK Regulations pages. EU Regulations and EASA Access Guides published by EASA no longer apply in the UK. Our website and publications are being reviewed to update all references. Any references to EU law and EASA Access guides should be disregarded and where applicable the equivalent UK versions referred to instead.

Whether you are building or interpreting a bowtie, the place to start is with the hazard.


This describes the potential source of harm being considered. It often describes a ‘normal’ aspect or activity within the operating environment and sets the context and scope of the bowtie, for example driving a car on a busy motorway – this is an environment where one is exposed to risks.

A hazard can be focused on:

  • a condition (e.g. icing conditions),
  • an object (e.g. another vehicle), or
  • an activity (e.g. driving).

Hazards are often part of normal business activities or environment and not necessarily something that can or should be terminated or eliminated. There is also the possibility to have more than one top event from one hazard as, for example, there would be several risk events associated with driving on a motorway.


The condition, object or activity with the potential of causing injuries to personnel, damage to equipment or structures, loss of material or reduction of ability to perform a prescribed function.

Guiding principles

  • In the description of the hazard consider setting the context and scope for the bowtie (e.g. defining the basic parameters within which the subsequent threats take place).
  • The ‘scope’ of the Bowtie can be likened to zooming in or out when taking a picture. It may be quite broad, where you capture the wider panorama, or it may be quite specific, where you zoom in on an area of concern.
  • The logical place to start is usually with the broad picture. However, if you find that you are not capturing the level of detail that is required for your purpose, it may mean it is time to revisit the hazard/ top event definition and zoom in.

Traps and tips

  • Trap: In referring to an organisation’s pre-existing traditional hazard register, confusion may arise as to what constitutes a hazard and what constitutes a threat. This comes about because these registers do not usually differentiate between the two.
    • Tip: It is quite common to find a mix of both threats and hazards in a traditional hazard register however the tendency is usually towards descriptions of threats. Remember that the hazard description is helping to set the scene for a risk assessment that is going to consider multiple threats.
  • Trap: Building bowties which are so large that their communication benefits are lost.
    • Tip: Be aware that there are practical considerations for the diagrams. For example, if you wish to print a hardcopy of the diagram, A0 is usually the maximum usable paper size. If the diagram is too large, the text size will be illegible once printed out.
    • Tip: If the diagram is getting too large, revisit the hazard, top event and threats to decide if you could achieve a better result with a different structure.