Threats & Errors – Threats & Errors

Swiss Cheese Analogy Model

James Reason compared serries of events that occur prior to an accident to a Trajectory either being ‘captured’ by defences or slipping through the holes in the swiss cheese. Most accidents are prevented by the cheese slices: organisational defences, oversight or management defences, polices, procedures or tools defences or finally the individuals operating.

As these defences are always moving and changing, so to is the models slices of cheese and the holes within the cheese. What captures an accident in one moment may not capture it the next moment.

Threats

Events or errors that occur outside the influence of the flight crew which have the potential to increase the operational complexity of the flight and require crew attention and management if safety margins are to be maintained. (University of Texas definition for multi-crew operations).

Errors

Actions or inactions that may lead to a deviation from crew or organisational intentions or expectations and may reduce safety margins and/or increase the probability of adverse operational events on the ground and/or during flight.

It maps how people avoid, detect, and manage:

• Threats
• Errors
• Undesirable Aircraft States

TEM can be used to describe behaviours and to investigate elements of performance It is also embedded into procedures e.g. Pre-flight briefings.

The “bikini model” is used to demonstrate how we can define strategies to resist and resolve threats to prevent undesirable consequences.

The key thing is to be able to identify the threats. Only then can we create a management STRATEGY (to mitigate threats).

• If we don’t identify the threat then we can fail to respond to it or exacerbate it and that becomes an ERROR.

An error must be identified. Only then can you RESIST the error (stop it as it happens) or RESOLVE it (correct the undesired aircraft state).

• If we don’t resist or resolve the error, there is a CONSEQUENCE in terms of undesired aircraft state
• Think of the Pre-flight briefing before each flight. What is the purpose?
• Status of the aircraft and crew (aircraft serviceability / fit to fly)
• “Fit to fly” will be covered in the fatigue module later.
• Turbulence/ Temperature/ Weather expected for the flight
• Operational considerations (flight times / Batteries / changes to SOPs)
• Threats (time pressure / public / birds)

This is the Threat and Error Management Model that we use. It is a conceptual framework for understanding operational performance in complex environments.

It shows us the role that crew can play in managing Threats and Errors and the potential consequences of our input or lack thereof. It highlights the importance of DETECTION and MANAGEMENT of Threats and Errors.