Safety factors in civil aircraft design requirements

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Safety factors in civil aircraft design requirements

Bristow, John W. / Irving, P.E.

Many factors influence the safety of modern civil aircraft. Some are related to design, others to the maintenance and operation of the aircraft. The technical requirements for Design are stated in Certification Specifications. These technical requirements are supported by a range of advisory material, colloquially known as advisory circulars, that offer acceptable means of compliance and interpretive guidance on most issues. The various levels of requirement are continually under review between the industry and the regulatory authorities in a harmonisation process. The factors and approaches employed vary with the type of aircraft. Those related to structural design relevant to large transport aircraft and to helicopters will be addressed in this paper. The means by which current and developing airworthiness requirements address these issues are summarised and examples given in respect of static, dynamic and cyclic loading. The relationship of safety factors to the probability of event occurrence is also covered in the context of the interaction between systems and structures. Safety factors can be explicit or implicit; requirements can be prescriptive or objective and the context in which they apply can be a regulated or 'free market' regime. In the case of civil aviation in Europe the regime is regulated, the requirements are fundamentally objective and safety factors are for the most part implied rather than specified.