**Description**
SAE ARP 4754A (2010), Guidelines for the Development of Civil Aircraft and System, introduced the terms Functional Failure Sets (FFS), Functional Development Assurance Level (FDAL) and Item Development Assurance Level (IDAL) into the processes used to support product development and certification. Section 5.2.3.2.3 of 4754A shows graphical examples of FDAL assignments, IDAL assignments and the resulting FFS that are used to show the proposed design may (or may not) meet the requirement set. The implication from 4754A seems to be the applicant needs both a “Development Assurance Level” fault tree diagram to address the concerns in 4754A and a “traditional” fault tree to address the concerns in SAE ARP 4761 (1996), Guidelines and Methods for Conducting the Safety Assessment Process on Civil Airborne Systems and Equipment.  The purpose of this paper is three-fold. First to address the above terms introduced 4754A and the term “Minimal Cut Set” from 4761. Second to show how these terms are related to the process steps in 4761 and the requirement set from the process described in 4754A. And lastly, provide the guidance that allows the reader to find the path that provides them the lowest risk for their certification program. While the examples presented in this paper use fault trees, the same methodology applies to the other techniques described in 4754A and 4761.

**Author(s) - ranked in descending order of contribution / as it should appear when published**
C. W. Robertson



Which presents greater risk to your certification program? Allocating and verifying Development Assurance Levels using the Functional Failure Sets from 4754A? Or using Fault Trees and Minimal Cut Sets from 4761?

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