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NASA NTRS2015

Planning the Unplanned Experiment: Towards Assessing the Efficacy of Standards for Safety-Critical Software

Safe use of software in safety-critical applications requires well-founded means of determining whether software is fit for such use. While software in industries such as aviation has a good safety record, little is known about whether standards for software in safety-critical applications 'work' (or even what that means). It is often (implicitly) argued that software is fit for safety-critical use because it conforms to an appropriate standard. Without knowing whether a standard works, such reliance is an experiment; without carefully collecting assessment data, that experiment is unplanned. To help plan the experiment, we organized a workshop to develop practical ideas for assessing software safety standards. In this paper, we relate and elaborate on the workshop discussion, which revealed subtle but important study design considerations and practical barriers to collecting appropriate historical data and recruiting appropriate experimental subjects. We discuss assessing standards as written and as applied, several candidate definitions for what it means for a standard to 'work,' and key assessment strategies and study techniques and the pros and cons of each. Finally, we conclude with thoughts about the kinds of research that will be required and how academia, industry, and regulators might collaborate to overcome the noted barriers.

Graydon, Patrick J.↗
NASA NTRS2015

Planning the Unplanned Experiment: Assessing the Efficacy of Standards for Safety Critical Software

We need well-founded means of determining whether software is t for use in safety-critical applications. While software in industries such as aviation has an excellent safety record, the fact that software aws have contributed to deaths illustrates the need for justi ably high con dence in software. It is often argued that software is t for safety-critical use because it conforms to a standard for software in safety-critical systems. But little is known about whether such standards `work.' Reliance upon a standard without knowing whether it works is an experiment; without collecting data to assess the standard, this experiment is unplanned. This paper reports on a workshop intended to explore how standards could practicably be assessed. Planning the Unplanned Experiment: Assessing the Ecacy of Standards for Safety Critical Software (AESSCS) was held on 13 May 2014 in conjunction with the European Dependable Computing Conference (EDCC). We summarize and elaborate on the workshop's discussion of the topic, including both the presented positions and the dialogue that ensued.

Graydon, Patrick J.↗
NASA NTRS1996

Software Reliability Issues Concerning Large and Safety Critical Software Systems

This research was undertaken to provide NASA with a survey of state-of-the-art techniques using in industrial and academia to provide safe, reliable, and maintainable software to drive large systems. Such systems must match the complexity and strict safety requirements of NASA's shuttle system. In particular, the Launch Processing System (LPS) is being considered for replacement. The LPS is responsible for monitoring and commanding the shuttle during test, repair, and launch phases. NASA built this system in the 1970's using mostly hardware techniques to provide for increased reliability, but it did so often using custom-built equipment, which has not been able to keep up with current technologies. This report surveys the major techniques used in industry and academia to ensure reliability in large and critical computer systems.

Kamel, Khaled↗
NASA NTRS2002

Formalized pilot study of safety-critical software anomalies: final report

This report describes both the research techniques and the application results from the analysis of safety-critical software anomalies recorded post-launch on seven spacecraft: Galileo, Mars Global Surveyor, Cassini/Huygens, Deep Space 1, Mars Climate Orbiter, Mars Polar Lander, and Stardust.

software anomalies pilot study software safety↗
NASA NTRS2011

Natural Language Interface for Safety Certification of Safety-Critical Software

Model-based design and automated code generation are being used increasingly at NASA. The trend is to move beyond simulation and prototyping to actual flight code, particularly in the guidance, navigation, and control domain. However, there are substantial obstacles to more widespread adoption of code generators in such safety-critical domains. Since code generators are typically not qualified, there is no guarantee that their output is correct, and consequently the generated code still needs to be fully tested and certified. The AutoCert generator plug-in supports the certification of automatically generated code by formally verifying that the generated code is free of different safety violations, by constructing an independently verifiable certificate, and by explaining its analysis in a textual form suitable for code reviews.

Denney, Ewen↗
NASA NTRS2006

Questioning the Role of Requirements Engineering in the Causes of Safety-Critical Software Failures

Many software failures stem from inadequate requirements engineering. This view has been supported both by detailed accident investigations and by a number of empirical studies; however, such investigations can be misleading. It is often difficult to distinguish between failures in requirements engineering and problems elsewhere in the software development lifecycle. Further pitfalls arise from the assumption that inadequate requirements engineering is a cause of all software related accidents for which the system fails to meet its requirements. This paper identifies some of the problems that have arisen from an undue focus on the role of requirements engineering in the causes of major accidents. The intention is to provoke further debate within the emerging field of forensic software engineering.

Johnson, C. W.↗
NASA NTRS2012

Certification of Safety-Critical Software Under DO-178C and DO-278A

The RTCA has recently released DO-178C and DO-278A as new certification guidance for the production of airborne and ground-based air traffic management software, respectively. Additionally, RTCA special committee SC-205 has also produced, at the same time, five other companion documents. These documents are RTCA DO-248C, DO-330, DO-331, DO- 332, and DO-333. These supplements address frequently asked questions about software certification, provide guidance on tool qualification requirements, and illustrate the modifications recommended to DO-178C when using model-based software design, object oriented programming, and formal methods. The objective of this paper is to first explain the relationship of DO-178C to the former DO-178B in order to give those familiar with DO- 178B an indication of what has been changed and what has not been changed. With this background, the relationship of DO-178C and DO-278 to the new DO-278A document for ground-based software development is shown. Last, an overview of the new guidance contained in the tool qualification document and the three new supplements to DO-178C and DO-278A is presented. For those unfamiliar with DO-178B, this paper serves to provide an entry point to this new certification guidance for airborne and ground-based CNS/ATM software certification.

Jacklin, Stephen A.↗
NASA NTRS2003

Certification Processes for Safety-Critical and Mission-Critical Aerospace Software

This document is a quick reference guide with an overview of the processes required to certify safety-critical and mission-critical flight software at selected NASA centers and the FAA. Researchers and software developers can use this guide to jumpstart their understanding of how to get new or enhanced software onboard an aircraft or spacecraft. The introduction contains aerospace industry definitions of safety and safety-critical software, as well as, the current rationale for certification of safety-critical software. The Standards for Safety-Critical Aerospace Software section lists and describes current standards including NASA standards and RTCA DO-178B. The Mission-Critical versus Safety-Critical software section explains the difference between two important classes of software: safety-critical software involving the potential for loss of life due to software failure and mission-critical software involving the potential for aborting a mission due to software failure. The DO-178B Safety-critical Certification Requirements section describes special processes and methods required to obtain a safety-critical certification for aerospace software flying on vehicles under auspices of the FAA. The final two sections give an overview of the certification process used at Dryden Flight Research Center and the approval process at the Jet Propulsion Lab (JPL).

Nelson, Stacy↗
NASA NTRS2003

Certification Processes for Safety-Critical and Mission-Critical Aerospace Software

This document is a quick reference guide with an overview of the processes required to certify safety-critical and mission-critical flight software at selected NASA centers and the FAA. Researchers and software developers can use this guide to jumpstart their understanding of how to get new or enhanced software onboard an aircraft or spacecraft. The introduction contains aerospace industry definitions of safety and safety-critical software, as well as, the current rationale for certification of safety-critical software. The Standards for Safety-Critical Aerospace Software section lists and describes current standards including NASA standards and RTCA DO-178B. The Mission-Critical versus Safety-Critical software section explains the difference between two important classes of software: safety-critical software involving the potential for loss of life due to software failure and mission-critical software involving the potential for aborting a mission due to software failure. The DO-178B Safety-critical Certification Requirements section describes special processes and methods required to obtain a safety-critical certification for aerospace software flying on vehicles under auspices of the FAA. The final two sections give an overview of the certification process used at Dryden Flight Research Center and the approval process at the Jet Propulsion Lab (JPL).

Nelson, Stacy↗
NASA NTRS1995

Software Safety Progress in NASA

NASA has developed guidelines for development and analysis of safety-critical software. These guidelines have been documented in a Guidebook for Safety Critical Software Development and Analysis. The guidelines represent a practical 'how to' approach, to assist software developers and safety analysts in cost effective methods for software safety. They provide guidance in the implementation of the recent NASA Software Safety Standard NSS-1740.13 which was released as 'Interim' version in June 1994, scheduled for formal adoption late 1995. This paper is a survey of the methods in general use, resulting in the NASA guidelines for safety critical software development and analysis.

Radley, Charles F.↗
NASA NTRS2008

Product Engineering Class in the Software Safety Risk Taxonomy for Building Safety-Critical Systems

When software safety requirements are imposed on legacy safety-critical systems, retrospective safety cases need to be formulated as part of recertifying the systems for further use and risks must be documented and managed to give confidence for reusing the systems. The SEJ Software Development Risk Taxonomy [4] focuses on general software development issues. It does not, however, cover all the safety risks. The Software Safety Risk Taxonomy [8] was developed which provides a construct for eliciting and categorizing software safety risks in a straightforward manner. In this paper, we present extended work on the taxonomy for safety that incorporates the additional issues inherent in the development and maintenance of safety-critical systems with software. An instrument called a Software Safety Risk Taxonomy Based Questionnaire (TBQ) is generated containing questions addressing each safety attribute in the Software Safety Risk Taxonomy. Software safety risks are surfaced using the new TBQ and then analyzed. In this paper we give the definitions for the specialized Product Engineering Class within the Software Safety Risk Taxonomy. At the end of the paper, we present the tool known as the 'Legacy Systems Risk Database Tool' that is used to collect and analyze the data required to show traceability to a particular safety standard

Hill, Janice↗