The DO-178B Level A Safety-Critical Guideline for Avionics Systems
What is DO-178B?
DO-178B is a software development guideline created jointly by the RTCA (Radio Technical Commission for Aeronautics) and the European Organization for Civil Aviation Equipment (EUROCAE) for safety-critical software used in aircraft. The EUROCAE equivalent to DO-178B is known as ED-12B. These internationally recognized guidelines outline the software design, code, and compliance documentation requirements for software deployed in an aircraft's safety-critical systems. The purpose of the guideline as it relates to software is to guarantee that the software is developed in a way that employs every measure possible to ensure that it will not cause or contribute to a catastrophic failure in the aircraft's functions.
The RTCA is a U.S. based Federal Advisory Committee with an international membership that includes many Tier 1 aerospace companies and government regulatory agencies such as the FAA and EASA. The DO-178B guideline has become the de facto Safety-Critical development standard in aviation. Several major RTOS manufacturers have introduced safety-critical versions of their operating systems designed specifically to address the DO-178B certification process. ALT's safety-critical software is designed to work with these safety critical RTOS and also supports a superset of the Khronos OpenGL ES-SC (Safety-Critical for Embedded Systems) API.
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ALT Software DO-178B Software Development Services
ALT's Development Services group offers custom development of DO-178B certifiable software for avionics systems. Our experience with safety critical driver development for audio, video, networking, electronics, mechanical controllers, as well as application porting and board support package development, combined with our access to hardware technical specifications make us an excellent choice for your safety-critical software development project. Our services include software design and development as well as the creation of all required certification artifacts.
Safety-Critical Software in Medical Devices and Automotive Environments
So far the DO-178B standard has been applied almost exclusively in the avionics industry, where failure in safety-critical systems could lead to catastrophic results. However, software that conforms to this guideline is often compatible with safety standards in other markets, such as FDA 510(k) or IEC 60601-1 standards for medical devices, and the IEC 61508 industrial safety standard for industrial and automotive devices. This cross-standards compatibility makes ALT Software's DO-178B Level A drivers well suited for virtually any safety-critical environment.
The DO-178B Level A Certification Process
The DO-178B Level A safety-critical guideline is targeted at software, which if fails or has anomalous behaviour, would prevent continued safe flight and landing, ie. result in a catastrophic failure. Level A is the highest of all criticality levels in DO-178B, requiring additional independence in verification activities and proof that 100% of the software structure is necessary, correct, and complete, which is more stringent than all lower levels. ALT Software's drivers are shipped as "certifiable". The reason we use the term "certifiable" instead of "certified" is because under RTCA guidelines only entire aircraft and aircraft engines can be "certified." The final "certified" product therefore is a complete aircraft comprised of all necessary certifiable components. The entire software life cycle is overseen by a Certification Liaison who examines documentation and monitors and audits the entire development lifecycle for compliance to DO-178B, and must approve the finished software product before it can undergo the approval process with the certification authorities.
Planning Documents and Traceability Artifacts
In order to facilitate certification of the aircraft, the driver must be bundled with supporting documentation referred to as "certification artifacts." Certification artifacts demonstrate that the software has been developed in accordance with DO-178B guidelines. The combination of the safety-critical driver and certification artifacts together comprise the "certifiable" driver.
The first set of certification artifacts are the planning documents. Before the first line of code can be written, a series of software planning documents must be produced and approved. The highest level planning document is the Plan for Software Aspects for Certification (PSAC). This document reflects the results of a high-level negotiation with the certification authority (e.g. the FAA in the U.S.) regarding the software development project.
With approval of the PSAC, the DO-178B software development group then develops a set of more detailed plans that will govern key processes. These are:
- Software Development Plan (SDP)
- Software Verification Plan (SVP)
- Software Configuration Management Plan (SCMP)
- Software Quality Assurance Plan (SQAP)
The Software Development Plan is supported by detailed standards that dictate how the software will be developed in order to meet the DO-178B criteria for software requirements, design, and coding. These are:
- Software Design Standards (SDS)
- Software Requirements Standards (SRS)
- Software Coding Standard (SCS)
The Software Verification Plan covers a major focus of DO-178B, namely verification. Virtually all software lifecycle activities must have an associated verification to detect and report errors that may have been introduced. By the end of the project, proof must exist showing that not only the software itself, but all plans, and procedures, requirements, design specifications, test cases, test results, and every single line of software code, has been verified for correctness.
Traceability is a key aspect of compliance to DO-178B which differentiates safety-critical software development from most software development projects. A large body of traceability and requirements documentation is developed and maintained in parallel with the software development process. This documentation proves that:
- The software completely satisfies all the specified system requirements.
- Every single code instruction of the software is necessary and serves its intended purpose.
- No unintended code exists in the software, and whatever non-essential code that may exist for portability, robustness or similar reasons will not detrimentally impact the software's reliability from a safety perspective.
The traceability and requirements documentation comprises a second level of certification artifacts that must be submitted for certification approval. Traceability evidence is generated and maintained using a software tool designed specifically for the purpose of tracking requirements and traceability.
Traceability evidence enables the auditors to verify that the code meets the lowest level requirements, and that those in turn meet higher level requirements, and so on, all the way up to the system level requirements. System level requirements are requirements that come from the system integrator/client and are generally related to major aircraft functions such as navigation or flight management and will cover both hardware and software aspects.
Coding, Testing, and SQA
Only when all the planning documents are complete can the first line of code be written. So when we say ALT's DO-178B Level A certifiable software is written "from the ground up," we really mean it.
All software development and artifact generation is monitored by the independent internal SQA (in addition to the certification liaison or client assigned auditor), who ensures that planned processes are being adhered to during every phase of development.
The result of all this planning, developing, testing, and auditing is a high performance driver that meets the highest internationally recognized standards for software reliability.
How ALT's modular driver architecture simplifies customization and recertification of software
Any changes to the driver require that it undergo a recertification process. This is where our drivers' modular architecture becomes most valuable. ALT's DO-178B drivers are composed of modules, each with its own complete certification artifacts. This enables us to customize the driver in a way that restricts both the customization and recertification effort to only those individual components that require modification. This reduces the development time and effort required for customization, which keeps the driver as close to a COTS product as possible, even when customization is required.
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Note: You may find DO-178B referred to incorrectly as "DO178B" or "D0-178B."