The human makes a vital contribution to system performance. Systems that do not support the human are prone to dramatic failure. In a survey of nine US Air Force Missile Systems, Shapero et al.((1)) found that human errors contributed from 20% to 53% of system failures; and Lee et al.((2)) cited studies of aviation, air traffic control, and nuclear power systems where 70-90% of system failures were either directly or indirectly attributable to the human component. Infamous examples include Three Mile Island, numerous aviation accidents labelled 'pilot error', and the USS 'Vincennes', where the crew's misunderstanding of information presented by the ship's sensors led to the shooting down of a commercial airliner, killing 290 passengers. As systems continue to become more complex, their full operational potential can be realized only if systems design capitalizes on human strengths and reduces the impact of human weaknesses. This is particularly important for military systems where personnel interact with lethal, safety critical, and valuable equipment, and the penalty for inadequate human performance con be loss of life. In addition to this, human factors input to systems design con greatly reduce life cycle costs by reducing training and maintenance requirements. Because training and maintenance activities are incurred repeatedly during the life cycle, the serving in life cycle costs will greatly outweigh any increase in development costs. This paper describes a methodology which can be applied to the systems engineering process to optimize the human contribution to mission performance. The elements of the methodology are derived from traditional human factors practice, which hers been documented in several sources including Def. Stam. 00-25((3)), MIL-STD-46855B((4)), STANAG 3994((5)), DoD-HDBK-763((6)) and NATO Defence Research Group((7)). The paper emphasises mechanisms for integrating these activities into systems design.
