The primary objective of this work is to investigate the necessity of a more comprehensive human factors approach to the Functional Hazard Assessment process in aircraft systems safety assessment. An overview of the aircraft design process is provided, covering some of its typical stages in a multidisciplinary design environment. Considering the emergence of increasingly complex and integrated aircraft, the role of safety requirements in a systems engineering approach is discussed, as well as the concepts of hazard, risk and safety, to support the analysis of the regulation framework related to aircraft systems safety assessment and certification. Currently adopted safety criteria and requirements, safety assessment standards, acceptable means of compliance, and guideline materials are covered. The discussion of the most important human factors perspectives, as a reflect of the need to understand humans interacting with complex systems, highlights then the problem to assess safety in those systems and points to objective means to incorporate an operational perspective to contribute to the improvement in current practices of the FHA process.