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During the final approach in a single-pilot aircraft, the pilot receives a wind shear warning in the cockpit. He/she decides, incorrectly, to continue the approach. The investigation of the incident concludes that the pilot was NOT aware of the procedure dictating a go-around.
This human error can be attributed to the following pair of the SHELL mode:

Liveware, representing the Commander and…

  • A
    Error representing pilots lack of familiarity with the procedures.
  • B
    Environment representing the weather conditions.
  • C
    Hardware representing the cockpit warning.
  • D
    Software representing the procedures.

Refer to figure.


The SHELL Model is a conceptual tool used to analyze the interaction of multiple system components and identify vulnerable spots. The SHELL Model contains the following four components:

  • Liveware (L). At the centre of the model is the pilot. Man - the most valuable and flexible component of the system. The second ‘L’ represents other humans whether inside or outside the aircraft.
  • Software (S). Includes procedures, training, support, manuals, checklist layouts, maps and charts, computer programmes.
  • Hardware (H). Relates to machines and equipment. Including cockpit layout, physical aircraft structure, instruments presentation and position of controls.
  • Environment (E). The working environment in which the rest of the L-H-S system must function - conditions both inside and outside the cockpit.

Interaction of different component of the SHELL Model:

Liveware-Hardware (L-H). The L-H interface, known as "man <=> machine" interface", refers to the relationship between the human and the physical attributes of equipment, machines and facilities.

Liveware-Software (L-S). The L-S interface is the relationship between the human and the supporting systems found in the workplace, e.g. regulations, manuals, checklists, publications, standard operating procedures (SOPs) and computer software. It includes such issues as recency of experience, accuracy, format and presentation, vocabulary, clarity and symbology.

Liveware-Liveware (L-L). The L-L interface is the relationship among persons in the work environment. Since flight crews, air traffic controllers, aircraft maintenance engineers and other operational personnel function in groups, it is important to recognize that communication and inter-personal skills, as well as group dynamics play a role in determining human performance.

Liveware-Environment (L-E). This interface involves the relationship between the human and both the internal and external environments. The internal workplace environment includes such physical considerations as temperature, ambient light, noise, vibration and air quality. The external environment includes operational aspects such as weather factors, aviation infrastructure and terrain. This interface also involves the relationship between the human internal environment and its external environment.

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