Abbreviation |
|
---|---|
Latest version | 5 January 2012 |
Organization | |
Predecessor | DO-178B |
Domain | Aviation |
DO-178C, Software Considerations in Airborne Systems and Equipment Certification is the primary document by which the certification authorities such as FAA, EASA and Transport Canada approve all commercial software-based aerospace systems. The document is published by RTCA, Incorporated, in a joint effort with EUROC and replaces DO-178B. The new document is called DO-178C/ED-12C and was completed in November 2011 and approved by the RTCA in December 2011. It became available for sale and use in January 2012. [1] [2] [3]
Except for FAR 33/JAR E, the Federal Aviation Regulations do not directly reference software airworthiness. [4] On 19 Jul 2013, the FAA approved AC 20-115C, designating DO-178C a recognized "acceptable means, but not the only means, for showing compliance with the applicable FAR airworthiness regulations for the software aspects of airborne systems and equipment certification." [5]
Since the release of DO-178B, there had been strong calls by FAA Designated Engineering Representatives (DERs) for clarification/refinement of the definitions and boundaries between the key DO-178B concepts of high-level requirements, low-level requirements, and derived requirements and a better definition of the exit/entry criteria between systems requirements and system design (see ARP4754) and that of software requirements and software design (which is the domain of DO-178B). Other concerns included the meaning of verification in a model-based development paradigm and considerations for replacing some or all software testing activities with model simulation or formal methods. The release of DO-178C and the companion documents DO-278A (Ground Systems), DO-248C (Additional information with rationale for each DO-178C objective), DO-330 (Tool Qualification), DO-331 (Modeling), DO-332 (Object Oriented), and DO-333 (Formal Methods) were created to address the issues noted. The SC-205 members worked with the SAE S-18 committee to ensure that ARP4754A and the above noted DO-xxx documents provide a unified and linked process with complementary criteria.
Overall, DO-178C keeps most of the DO-178B text, which has raised concerns that issues with DO-178B, such as the ambiguity about the concept of low-level requirements, may not be fully resolved. [6]
The RTCA/EUROCAE joint committee work was divided into seven Subgroups:
The Model Based Development and Verification subgroup (SG4) was the largest of the working groups. All work is collected and coordinated via a web-site that is a collaborative work management mechanism. [7] Working artifacts and draft documents were held in a restricted area available to group members only.
The work was focused on bringing DO-178B/ED-12B up to date with respect to current software development practices, tools, and technologies. [8] [9]
The Software Level, also known as the Development Assurance Level (DAL) or Item Development Assurance Level (IDAL) as defined in ARP4754 (DO-178C only mentions IDAL as synonymous with Software Level [10] ), is determined from the safety assessment process and hazard analysis by examining the effects of a failure condition in the system. The failure conditions are categorized by their effects on the aircraft, crew, and passengers.
DO-178C alone is not intended to guarantee software safety aspects. Safety attributes in the design and as implemented as functionality must receive additional mandatory system safety tasks to drive and show objective evidence of meeting explicit safety requirements. The certification authorities require and DO-178C specifies the correct DAL be established using these comprehensive analyses methods to establish the software level A-E. "The software level establishes the rigor necessary to demonstrate compliance" with DO-178C. [10] Any software that commands, controls, and monitors safety-critical functions should receive the highest DAL - Level A.
The number of objectives to be satisfied (some with independence) is determined by the software level A-E. The phrase "with independence" refers to a separation of responsibilities where the objectivity of the verification and validation processes is ensured by virtue of their "independence" from the software development team. For objectives that must be satisfied with independence, the person verifying the item (such as a requirement or source code) may not be the person who authored the item and this separation must be clearly documented. [11]
Level | Failure condition | Objectives [12] | With independence |
---|---|---|---|
A | Catastrophic | 71 | 30 |
B | Hazardous | 69 | 18 |
C | Major | 62 | 5 |
D | Minor | 26 | 2 |
E | No Safety Effect | 0 | 0 |
Processes are intended to support the objectives, according to the software level (A through D—Level E was outside the purview of DO-178C). Processes are described as abstract areas of work in DO-178C, and it is up to the planners of a real project to define and document the specifics of how a process will be carried out. On a real project, the actual activities that will be done in the context of a process must be shown to support the objectives. These activities are defined by the project planners as part of the Planning process.
This objective-based nature of DO-178C allows a great deal of flexibility in regard to following different styles of software life cycle. Once an activity within a process has been defined, it is generally expected that the project respect that documented activity within its process. Furthermore, processes (and their concrete activities) must have well defined entry and exit criteria, according to DO-178C, and a project must show that it is respecting those criteria as it performs the activities in the process.
The flexible nature of DO-178C's processes and entry/exit criteria make it difficult to implement the first time, because these aspects are abstract and there is no "base set" of activities from which to work. The intention of DO-178C was not to be prescriptive. There are many possible and acceptable ways for a real project to define these aspects. This can be difficult the first time a company attempts to develop a civil avionics system under this standard, and has created a niche market for DO-178C training and consulting.
For a generic DO-178C based process, Stages of Involvements (SOI) are the minimum gates that a Certification Authority gets involved in reviewing a system or sub-system as defined by EASA on the Certification Memorandum SWCEH – 002: SW Approval Guidelines and FAA on the Order 8110.49: SW Approval Guidelines.
DO-178 requires documented bidirectional connections (called traces) between the certification artifacts. For example, a Low Level Requirement (LLR) is traced up to a High Level Requirement (HLR) it is meant to satisfy, while it is also traced to the lines of source code meant to implement it, the test cases meant to verify the correctness of the source code with respect to the requirement, the results of those tests, etc. A traceability analysis is then used to ensure that each requirement is fulfilled by the source code, that each functional requirement is verified by test, that each line of source code has a purpose (is connected to a requirement), and so forth. Traceability analysis accesses the system's completeness. The rigor and detail of the certification artifacts is related to the software level.
SC-205/WG-12 was responsible for revising DO-178B/ED-12B to bring it up to date with respect to current software development and verification technologies. The structure of the document remains largely the same from B to C. Example changes include: [13]
DO-178B was not completely consistent in the use of the terms guidelines and guidance within the text. "Guidance" conveys a slightly stronger sense of obligation than "guidelines". As such, with the DO-178C, the SCWG has settled on the use of "guidance" for all the statements that are considered as "recommendations", replacing the remaining instances of "guidelines" with "supporting information" and using that phrase wherever the text is more "information" oriented than "recommendation" oriented.
The entire DO-248C/ED-94C document, Supporting Information for DO-178C and DO-278A, falls into the "supporting information" category, not guidance. [18]
Chapter 6.1 defines the purpose for the software verification process. DO-178C adds the following statement about the Executable Object Code:
As a comparison, DO-178B states the following with regard to the Executable Object Code:
The additional Revision C clarification filled a gap that a software developer could have encountered when interpreting the Revision B document. [19]
In software engineering, code coverage, also called test coverage, is a percentage measure of the degree to which the source code of a program is executed when a particular test suite is run. A program with high code coverage has more of its source code executed during testing, which suggests it has a lower chance of containing undetected software bugs compared to a program with low code coverage. Many different metrics can be used to calculate test coverage. Some of the most basic are the percentage of program subroutines and the percentage of program statements called during execution of the test suite.
Avionics software is embedded software with legally mandated safety and reliability concerns used in avionics. The main difference between avionic software and conventional embedded software is that the development process is required by law and is optimized for safety. It is claimed that the process described below is only slightly slower and more costly than the normal ad hoc processes used for commercial software. Since most software fails because of mistakes, eliminating the mistakes at the earliest possible step is also a relatively inexpensive and reliable way to produce software. In some projects however, mistakes in the specifications may not be detected until deployment. At that point, they can be very expensive to fix.
DO-178B, Software Considerations in Airborne Systems and Equipment Certification is a guideline dealing with the safety of safety-critical software used in certain airborne systems. It was jointly developed by the safety-critical working group RTCA SC-167 of the Radio Technical Commission for Aeronautics (RTCA) and WG-12 of the European Organisation for Civil Aviation Equipment (EUROCAE). RTCA published the document as RTCA/DO-178B, while EUROCAE published the document as ED-12B. Although technically a guideline, it was a de facto standard for developing avionics software systems until it was replaced in 2012 by DO-178C.
A hazard analysis is one of many methods that may be used to assess risk. At its core, the process entails describing a system object that intends to conduct some activity. During the performance of that activity, an adverse event may be encountered that could cause or contribute to an occurrence. Finally, that occurrence will result in some outcome that may be measured in terms of the degree of loss or harm. This outcome may be measured on a continuous scale, such as an amount of monetary loss, or the outcomes may be categorized into various levels of severity.
ARP4761, Guidelines for Conducting the Safety Assessment Process on Civil Aircraft, Systems, and Equipment is an Aerospace Recommended Practice from SAE International. In conjunction with ARP4754, ARP4761 is used to demonstrate compliance with 14 CFR 25.1309 in the U.S. Federal Aviation Administration (FAA) airworthiness regulations for transport category aircraft, and also harmonized international airworthiness regulations such as European Aviation Safety Agency (EASA) CS–25.1309.
ARP4754, Aerospace Recommended Practice (ARP) ARP4754B, is a guideline from SAE International, dealing with the development processes which support certification of Aircraft systems, addressing "the complete aircraft development cycle, from systems requirements through systems verification." Revision A was released in December 2010. It was recognized by the FAA through Advisory Circular AC 20-174 published November 2011. EUROCAE jointly issues the document as ED–79.
RTCA DO-254 / EUROCAE ED-80, Design Assurance Guidance for Airborne Electronic Hardware is a document providing guidance for the development of airborne electronic hardware, published by RTCA, Incorporated and EUROCAE. The DO-254/ED-80 standard was formally recognized by the FAA in 2005 via AC 20-152 as a means of compliance for the design assurance of electronic hardware in airborne systems. The guidance in this document is applicable, but not limited, to such electronic hardware items as
Software safety is an engineering discipline that aims to ensure that software, which is used in safety-related systems, does not contribute to any hazards such a system might pose. There are numerous standards that govern the way how safety-related software should be developed and assured in various domains. Most of them classify software according to their criticality and propose techniques and measures that should be employed during the development and assurance:
Functional safety is the part of the overall safety of a system or piece of equipment that depends on automatic protection operating correctly in response to its inputs or failure in a predictable manner (fail-safe). The automatic protection system should be designed to properly handle likely systematic errors, hardware failures and operational/environmental stress.
LDRA, previously known as the Liverpool Data Research Associates, is a privately held company producing software analysis, testing, and requirements traceability tools for the public and private sectors. It is involved static and dynamic software analysis.
AC 25.1309–1 is an FAA Advisory Circular (AC) 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.
Cantata++, commonly referred to as Cantata in newer versions, is a commercial computer program designed for dynamic testing, with a focus on unit testing and integration testing, as well as run time code coverage analysis for C and C++ programs. It is developed and marketed by QA Systems, a multinational company with headquarters in Waiblingen, Germany.
The Advisory Circular AC 20-115( ), Airborne Software Development Assurance Using EUROCAE ED-12( ) and RTCA DO-178( ), recognizes the RTCA published standard DO-178 as defining a suitable means for demonstrating compliance for the use of software within aircraft systems. The present revision D of the circular identifies ED-12/DO-178 Revision C as the active revision of that standard and particularly acknowledges the synchronization of ED-12 and DO-178 at that revision.
FAA Order 8110.105B, Airborne Electronic Hardware Approval Guidelines is an explanation of how Federal Aviation Administration (FAA) personnel can use and apply the publication
The Advisory Circular AC 20-152A, Development Assurance for Airborne Electronic Hardware, identifies the RTCA-published standard DO-254 as defining "an acceptable means, but not the only means" to secure FAA approval of electronic hardware for use within the airspace subject to FAA authority. Commonly, the DO-254 has been interpreted as applying to complex custom micro-coded components within aircraft systems with Item Design Assurance Levels (IDAL) of A, B, or C. However, Revision A of this AC clarifies that AC 20-152 and DO-254 applies to all type certification of all electronic hardware aspects of airborne systems, including all electronic hardware that is not complex, that is, "simple electronic devices". Revision A also defines objectives in addition to those identified in DO-254; applicants choosing to follow DO-254 under the authority of AC 20-152A must also accomplish these additional objectives.
DO-248C, Supporting Information for DO-178C and DO-278A, published by RTCA, Incorporated, is a collection of Frequently Asked Questions and Discussion Papers addressing applications of DO-178C and DO-278A in the safety assurance of software for aircraft and software for CNS/ATM systems, respectively. Like DO-178C and DO-278A, it is a joint RTCA undertaking with EUROCAE and the document is also published as ED-94C, Supporting Information for ED-12C and ED-109A. The publication does not provide any guidance additional to DO-178C or DO-278A; rather, it only provides clarification for the guidance established in those standards. The present revision is also expanded to include the "Rationale for DO-178C/DO-278A" section to document items that were considered when developing DO-178B and then DO-178C, DO-278A, and DO-330, as well as the supplements that accompany those publications.
DO-297, Integrated Modular Avionics (IMA) Development Guidance and Certification Considerations is one of the primary document by which certification authorities such as the FAA and EASA approve Integrated Modular Avionics (IMA) systems for flight. The FAA Advisory Circular (AC) 20-170 refers to DO-297.
The Advisory Circular AC 00-69, Best Practices for Airborne Software Development Assurance Using EUROCAE ED-12( ) and RTCA DO-178( ), initially issued in 2017, supports application of the active revisions of ED-12C/DO-178C and AC 20-115. The AC does not state FAA guidance, but rather provides information in the form of "best practices" complementary to the objectives of ED-12C/DO-178C.
The Certification Authorities Software Team (CAST) is an international group of aviation certification and regulatory authority representatives. The organization of has been a means of coordination among representatives from certification authorities in North and South America, Europe, and Asia, in particular, the FAA and EASA. The focus of the organization has been harmonization of Certification Authorities activities in part though clarification and improvement of the guidance provided by DO-178C and DO-254.
CAST-15, Merging High-Level and Low-Level Requirements is a Certification Authorities Software Team (CAST) Position Paper. It is an FAA publication that "does not constitute official policy or guidance from any of the authorities", but is provided to applicants for software and hardware certification for educational and informational purposes only.
{{cite web}}
: CS1 maint: numeric names: authors list (link)The industry expects the final package —DO-178C— to be released in the first quarter of 2011 and be mandated six to nine months after ratification.
The release of these long anticipated standards will occur in mid 2011 and be recognized by the Certification Authorities in 2012.
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: CS1 maint: archived copy as title (link)DO-178C will contain more details on software modeling and the potential ability to use modeling to supplant some of the verification techniques normally required in DO-178B. DO-178C will also more fully address OO (Object Oriented) software and the conditions under which it can be used and the certification ramifications of OO in DO-178C.