Perspectives: Software Specs: The Next Step

Software is taking on larger, more complex aviation tasks and is playing an increasingly larger role in aviation safety. Its development also is evolving. Software developers need updated materials to help them prepare new aviation software, and aviation regulators around the world need updated guidance materials as they strive to assure that new or modified software is "safe" and can be certified for operational use. That's what RTCA's software development activities and products are all about.

Guidance Needed

Airborne system software was introduced in the 1970s. By the late `70s, it was clear that regulators needed industry-accepted guidance to help them confirm the airworthiness of this software. RTCA Special Committee 145 was established, adding an important new dimension to RTCA's work. The committee was tasked to develop guidance material that FAA could use as a means of determining the proper development and use of the software that resides in airborne systems and equipment.

The evolution of aviation-related software resulted in the need for other RTCA special committees and, in 1992, the publication of RTCA document DO-178B, "Software Considerations in Airborne Systems and Equipment." FAA issued advisory circular, AC 20-115B, which formally recognizes DO-178B as an acceptable means of compliance for the development of airborne systems and equipment software.

The RTCA document has been successfully used to evaluate the safety of new or modified airborne system software in the United States and around the world. It also has been used as a basis for RTCA DO-278, "Guidelines for Communications, Navigation, Surveillance, and Air Traffic Management (CNS/ATM) Systems Software Integrity Assurance," which guides software development for ground-based aviation systems. The U.S. military and the automotive industry have used DO-178B in their own embedded software domains.

Transatlantic Effort

Like other aspects of aviation electronics, software technology and methods continue to evolve. In the fall of 2004 RTCA invited several U.S. and European aviation software domain experts to consider the current status and expected evolutionary path of aviation-related software, and to determine if an update to DO-178B was needed. After three days of deliberation, the group agreed that an update is needed. They went on to say that the update should not only address emerging software trends and technologies, but that it should more efficiently address technology changes while not altering the document's technology-neutral approach to software development.

As many have noted, the current object-oriented design technology modifies the traditional functional-based approach to aviation software development. FAA has raised issues concerning the deterministic behavior of software development using object-oriented technology. The agency has noted that DO-178B's object-oriented approach to meeting requirements and tracking the development of software design and coding can be difficult.

Other software methods, such as model-based design, provide opportunities for reducing the verification costs of software-intensive airborne systems. DO-178B provides little guidance for such an approach, and as such, FAA must make a case-by-case assessment as to the safety of systems developed with such methods.

DO-178C

RTCA formed Special Committee 205, Software Considerations in Aeronautical Systems, to update DO-178B and to recommend provisions for accommodating software technology trends. The new guidance document will be identified as DO-178C. Special Committee 205 is a joint activity with WG-71 of the European Organisation for Civil Aviation Equipment (EUROCAE). Their combined efforts will help harmonize the development and use of avionics software in the global environment.

SC-205 met for the first time during March 2005 and plans to deliver DO-178C in 2008. The new document is expected to do the following:

-Provide a more consistent application of certification requirements,

-Clarify the boundaries between systems and software guidance,

-Consolidate numerous regulatory and industry documents, and

-Reduce certification risks.

As with all RTCA Special Committee activities, meetings are "open" to all interested individuals. We encourage your participation.

David S. Watrous is president of RTCA Inc.