Accident Causation Models FLT 241


Modern aviation safety theorists have been led by ICAO and the FAA to embrace a new way of thinking to prevent aviation accidents and increase awareness of aviation safety concepts. These experts have focused on questions such as:

Why did the accident happen?
How can we prevent future accidents?

Since the turn of the century, aviation accident investigations has matured from assigning blame to the following thinking regarding accident prevention: Instead of reacting to accidents and punishing the guilty party for failure to act safely, modern safety thinking has become proactive and even predictive of where and when the next accident may occur if current trends continue.

Purpose of Accident Modeling

  • Help explain the relationship between hazards and accidents.
  • Assist with understanding and explaining reality.
  • Aid in visualizing things that cannot be directly observed.
  • Must approximate conditions that exist in reality to be useful.

Reason's SWISS CHEESE Model

Features of the Swiss Cheese Model

  • Systems are protected by multiple layers of defenses that are designed to prevent hazards or system failures from cascading into accidents.
  • Each layer of protection, however can develop "holes" or flaws through safety deficiencies, resembling swiss cheese.
  • as the number and size of these holes in the defenses increase, the chances of accidents also increase.
  • When the holes in each of the layers of defenses line up, an accident occurs.

Real World Problems Using Reason's Swiss Cheese Model

Organizational Influences

  • Rapid Expansion
  • Lack of Regulation
  • Management "lip service" to safety

Unsafe Supervision

  • Risks and hazards neglected
  • Poor work scheduling- fatigue
  • Insufficient training

Preconditions for Unsafe Acts

  • High workload
  • Time pressure to perform tasks
  • Ignorance of the system

Unsafe Acts

  • Aircraft warining system disabled
  • Ommission of critical checklaist item
  • Over- reliance on automation

The SHELL Model

  • Liveware to Software- The relationship between the human and supporting systems found in the workplace. Not just computer programs, these include user friendly issues in regulation, manuals and checklists.
  • Liveware to Hardware- The relationship between man and machine. Although humans adapt well to poor interfaces, they can easily cause safety hazards if not well designed.
  • Liveware to Liveware- This is the relationship between the human and other people in the workplace. Communication styles and techniques are important here.
  • Liveware to Environment- The relationship between the human and the internal and external environments.

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