systems. It is the ATO’s intent that all new non-airborne systems and modified legacy systems treated as new acquisitions in the NAS are developed in accordance with RTCA DO-278A. 

The Program Office (PO) must conduct a software assurance compliance analysis for each component of a system going through the AMS process that contains software. If the program involves legacy software components that were not developed to the requirements of RTCA DO-278A, the PO must conduct a compliance gap analysis for each component of a modified legacy system that contains software. A vendor may choose to submit to the PO a self-assessed compliance gap analysis on one of the existing products in support of the contract award. 

The only difference between a software assurance compliance analysis and a compliance gap analysis is that the gap analysis is conducted on a previously completed project to ensure a program’s work will pass future compliance evaluations, and the compliance analysis is conducted on a new product while it is being developed. The purpose of the gap analysis is to update a system developer’s processes and identify specific activities that must be addressed to ensure the processes and product are compliant. 

It is important to note that many of the non-airborne CNS/ATM systems currently in the NAS were developed and fielded using integrity assurance guidelines other than those contained in RTCA DO-278A. Reasons for having used alternative guidelines include: 

• RTCA DO-278A was not yet developed or was not yet widely accepted, and the system developers / subcontractors did not conduct safety analyses for the software components of the system. 

• Other software development standards (e.g., DOD-STD-2167A, MIL-STD-498, EIA 12207, or FAA-STD-026A) were used to implement the software development process. 

• RTCA DO-178 (the airborne systems equivalent of RTCA DO-278) was used to evaluate the development of non-airborne CNS/ATM systems. 

If systems previously developed/fielded using alternative guidelines are modified under a new acquisition, the PO must evaluate new and affected software for compliance with RTCA DO-278A. 

## 4 Compliance with the Standard 

RTCA DO-278A was developed by the aviation industry and contains guidance and best practices for developing software. This section describes the nature of content in RTCA DO-278A and how to use the guidance therein when identifying requirements. 

## 4.1 RTCA DO-278A Guidance and Objectives 

## 4.1.1 Objective Guidance 

Objective guidance is specific, and compliance to this guidance can be easily observed during audit activities. Ensuring compliance to objective guidance is done by identifying evidence that a requirement has been satisfied. For example, if the guidance requires each configuration 

