On September 30, 2011, certification authorities released Advisory Circular 20-174[1], Development of Civil Aircraft and Systems, which recognizes the Society of Automotive Engineers (SAE) Aerospace Recommended Practice (ARP) 4754A and the European equivalent ED-79A [2], in order to address "the concern of possible development errors due to the ever increasing complexity of modern aircraft and systems." ARP4754A/ED-79A describes a process of development assurance which helps reduce the risk of design errors in the development of aircraft systems. This process is necessary for complex systems not easily comprehended by deterministic analyses or tests. This ARP was developed "in the context of Title 14 of the Code of Federal Regulations (14 CFR) part 25," a category which includes complex systems such as full fly-by-wire flight controls. However, this paper shows that such systems are the exception to most, recent civil airplane designs. Of new airplanes designed in the last 10 years, most implement systems which are simple and easily comprehended. Many of these simpler aircraft are in the part 23 category, which the AC also associates to this ARP. This paper shows that the ARP, as written, does not consider simple systems and may unnecessarily burden the development of such systems through this lack of recognition. This paper reviews the current diversity of system complexity, discusses the regulatory and technical drivers for this diversity, and provides recommendations for incorporating such considerations in the ARP while preserving its original intent.
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