Description

ICAO SHELL Model, as described in ICAO Doc 9859, Safety Management Manual, is a conceptual tool used to analyse the interaction of multiple system components. It also refers to a framework proposed in ICAO Circular 216-AN31.

The concept (the name being derived from the initial letters of its components, Software, Hardware, Environment, Liveware) was first developed by Edwards in 1972, with a modified diagram to illustrate the model developed by Hawkins in 1975.

One practical diagram to illustrate this conceptual model uses blocks to represent the different components of Human Factors. This building block diagram does not cover the interfaces which are outside Human Factors (hardware-hardware; hardware-environment; software-hardware) and is only intended as a basic aid to understanding Human Factors: