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AC 25.1309–1 is an FAA Advisory Circular (AC) (Subject: System Design and Analysis) that identifies acceptable means for showing compliance with the airworthiness requirements of § 25.1309 of the Federal Aviation Regulations. Revision A was released in 1988. In 2002, work was done on Revision B, but it was not formally released; the result is the Rulemaking Advisory Committee-recommended revision B-Arsenal Draft (2002). The Arsenal Draft is "considered to exist as a relatively mature draft". The FAA and EASA have subsequently accepted proposals by type certificate applicants to use the Arsenal Draft on development programs. AC 25.1309–1 establishes the principle that the more severe the hazard resulting from a system or equipment failure, the less likely that failure must be. Failures that are catastrophic must be extremely improbable. Airworthiness standards The airworthiness requirements for transport category airplanes are contained in Title 14, Code of Federal Regulations (14 CFR) part 25 (commonly referred to as part 25 of the Federal Aviation Regulations (FAR)). Manufacturers of transport category airplanes must show that each airplane they produce of a given type design complies with the relevant standards of part 25. AC 25.1309–1 describes acceptable means for showing compliance with those airworthiness requirements. It recognizes Aerospace Recommended Practices ARP4754 and ARP4761 (or their successors) as such means: ARP4754A, Guidelines For Development Of Civil Aircraft and Systems, is a guideline from SAE International, dealing with the development processes which support certification of Aircraft systems. This ARP further recognizes integration of DO-297, DO-178, and DO-254 into the guidelines for development and recognizes ARP5150/5151 as guidelines for in-service operation and maintenance. ARP4761, Guidelines and Methods for Conducting the Safety Assessment Process On Civil Airborne Systems and Equipment Background AC 25.1309–1 provides background for important concepts and issues within airplane system design and analysis. Catastrophic failure condition rate The circular provides a rationale for the upper limit for the Average Probability per Flight Hour for Catastrophic Failure Conditions of 1 x 10−9 or "Extremely Improbable". Failure Conditions resulting in relatively more severe effects must be relatively less likely to occur; that is, an inverse relationship between severity and likelihood should be a safety objective of aviation system design. Fail-Safe Design Concept This AC presents the FAA Fail-Safe Design Concept, which applies basic objectives pertaining to failures: Failures of any system should be assumed for any given flight regardless of probability and such failures "should not prevent continued safe flight and landing" or otherwise significantly reduce safety. Subsequent failure during the same flight should also be assumed. The AC lists design principles or techniques used to ensure a safe design. Usually, a combination of at least two safe design techniques are needed to provide a fail-safe design; i.e. to ensure that Major Failure Conditions are Remote, Hazardous Failure Conditions are Extremely Remote, and Catastrophic Failure Conditions are Extremely Improbable. Highly integrated systems With the emergence of highly integrated systems that perform complex and interrelated functions, particularly through the use of electronic technology and software-based techniques [e.g., Integrated Modular Avionics (IMA) ], concerns arose that traditionally quantitative functional-level design and analysis techniques previously applied to simpler systems were no longer adequate. As such the AC includes expanded, methodical approaches, both qualitative and quantitative, that consider the integration of the "whole airplane and its systems". Definitions and Classifications A main task of AC 25.1309–1 is to provide standard definitions of terms (including hazard and probability classifications) for consistent use throughout the framework set up for the accomplishment of functional airplane safety. Where regulations (FAR) and standards (ARP) may use such terms as failure condition, and extremely improbable, AC 25.1309–1 defines their specific meanings. In this respect, AC 25.1309–1 is comparable to ISO 26262–1 Vocabulary, at least in regard to the relative dependent standards. Key definitions include: Error, Failures, and Failure Conditions The re-introduction of Error to the AC recognizes the role of human error (in development, manufacture, operation, or maintenance) as a source of system failures, especially in complex and integrated avionics. The term Failure Conditions provides for a focus on the effects of a failure separate from the causes. Classification of failure conditions by severity of effect Catastrophic, Hazardous, Major, Minor, or No Safety Effect A Catastrophic Failure condition is one "which would result in multiple fatalities, usually with the loss of the airplane." Definition of Probability Terms Extremely Improbable, Extremely Remote, Remote, or Probable An Extremely Improbable failure condition is one so unlikely that it is not anticipated to occur during the entire operational life of all airplanes of one type. Quantitatively, these probability terms are define as follows: Extremely Improbable (10−9 or less), Extremely Remote (10−7 or less), Remote (10−5 or less), Probable (more than 10−5). Safety objectives Classified failure conditions are assigned qualitative and quantitative safety objectives, giving guidance to development and operation. Quantitative safety objectives The AC defines the acceptable safety level for equipment and systems as installed on the airplane and establishes an inverse relationship between Average Probability per Flight Hour and the severity of Failure Condition effects: Failure Conditions with No Safety Effect have no probability requirement. Minor Failure Conditions may be Probable. Major Failure Conditions must be no more frequent than Remote. Hazardous Failure Conditions must be no more frequent than Extremely Remote. Catastrophic Failure Conditions must be Extremely Improbable. The safety objectives associated with Catastrophic Failure Conditions may be satisfied by demonstrating that: No single failure will result in a Catastrophic Failure Condition; and Each Catastrophic Failure Condition is extremely improbable. Qualitative safety objectives The failure conditions Catastrophic through No Safety Effect are assigned Functional and Item Design Assurance Levels (DAL) A, B, C, D, E, respectively, with the concept that there is less tolerance for undiscovered design error in systems with more severe failure effects. In this manner, development of systems and components contributing to more severe effects are subject to increasingly rigorous assurances of effective prevention, detection, and removal of design error, DAL A representing the most thorough assurance rigor. History.... Discover the Cary Spitzer Uma Ferrell Thomas Ferrell popular books. Find the top 100 most popular Cary Spitzer Uma Ferrell Thomas Ferrell books.