The DO-178B, titled Software Considerations in Airborne Systems and Equipment Certification, was a document published jointly by RTCA and the European Organization for Civil Aviation Equipment (EUROCAE). Certification authorities such as the Federal Aviation Administration (FAA) in the United States used this document as the standard for approving commercial aerospace systems. Effective January 2012, the 178B was replaced by the DO-178C.
What are DO-178 and DO-254?
The DO-178C is currently used for avionics software development and testing the applications and reliability of such software. The 178C was implemented to improve terminology over the 178B as well as to ensure all standards were up to date with modern electromechanical systems and best practices.
Conversely, the DO-254 is the document that provides guidelines for the development of electronic aviation hardware. In this context, hardware can refer to things like circuit boards, integrated technology components (like chip modules), and any easily replaceable units. The DO-254 has been officially recognized by the FAA since 2005. The 178C and 254 documents have unique versions intended for military aircraft vs. commercial use.
DO-178C Changes
The 178C changed inconsistent terms such as “objectives” and “goals” to read more consistently and provided an updated and more detailed glossary of terms compared to the 178B. The 178C also added multiple changes to the index, most notably with development assurance levels.
Level A: These are the critical flight electronics. Failures or malfunctions in these components would cause severely unsafe conditions that would likely result in the death of those aboard the aircraft.
Level B: This level pertains to flight hardware whose failure or malfunction would create seriously unsafe conditions that could result in death.
Level C: This level represents flight electronics where failure or malfunction could result in major injuries.
Level D: This level represents flight hardware whose failure or malfunction could result in minor injuries.
Level E: Non-critical flight components that will have no immediate effect on the aircraft.
The 178C added more objectives for components at levels A, B, and C as well as further clarification in level A’s 9th objective: “Verification of additional code, that cannot be traced to Source Code, is achieved.”
DO-254 Hardware Descriptions
254 provides guidelines for hardware development based on a variety of criteria. At its most basic, the document splits hardware components into two categories: simple and complex.
Simple Hardware Items: Hardware is classified as simple if “a comprehensive combination of deterministic tests and analyses can ensure correct functional performance under all foreseeable operating conditions with no anomalous behavior.”
Complex Hardware Items: Hardware is automatically classed as complex if it fails to meet the definition of a simple item. In other words, complex items have less predictable behavior than simple ones.
The body of DO-254 further demonstrates efficient ways to achieve process assurance for complex items. This is often done by an outside organization or expert authorized to carry out quality assurance checking.
Training Options
If you need it, you can receive DO-178C Training through AFuzion. They also offer a training course for DO-254 and other documents including the ARP-4754A. They provide attendees with training on system development, certification, and safety compliance. Practice areas include avionics software development, aviation safety, transportation, and automotive training, and more. AFuzion publications are used by the vast majority of companies to achieve avionics certification with the FAA and EASA.
Overall, the purpose of documents like the 178C and 254 is to provide practical and cost-effective guidelines that are flexible enough to be used with varying development models. The 178, in particular, is written by industry professionals with little government oversight, so it’s as informative and easy to read as possible. With improved 178C standards, software developers and users know that their equipment is as reliable as it can be.
