There are five D0/178B criticality levels, with DO-178B Level A being most critical and DO-178B Level E being least critical. The DO-178B criticality level is based upon the contribution of the associated software to potential failure conditions. DO-178B failure conditions are determined by the FAA system safety assessment process. Each avionics system has one defined criticality level (and must be approved by the FAA); however, different components within that system can have differing criticality levels subject to certain guidelines. The higher the DO-178B criticality level, the greater the amount of software development effort required. Our DO-178B Training provides additional details on DO-178B criticality levels and how to determine, apply and optimize. Additional information on each DO-178B critical level are provided below.

DO-178B Level A software is software whose anomalous behavior, as shown by the system safety assessment process, would cause or contribute to a failure of system function resulting in a catastrophic failure condition for the aircraft. Failure of DO-178B Level A software could be typified by total loss of life. Approximately 20-30% of avionics systems and 40% of avionics software code must meet DO-178B Level A criteria.

DO-178B Level B software is software whose anomalous behavior, as shown by the system safety assessment process, would cause or contribute to a failure of system function resulting in a hazardous/severe-major failure condition for the aircraft. Failure of DO-178B Level B software could be typified by some loss of life. Approximately 20% of avionics systems and 30% of avionics software code must meet DO-178B Level B criteria.

DO-178B Level C software is software whose anomalous behavior, as shown by the system safety assessment process, would cause or contribute to a failure of system function resulting in a major failure condition for the aircraft. Failure of DO-178B Level C software could be typified by serious injuries. Approximately 25% of avionics systems and 20% of avionics software code must meet DO-178B Level C criteria.

DO-178B Level D software is software whose anomalous behavior, as shown by the system safety assessment process, would cause or contribute to a failure of system function resulting in a minor failure condition for the aircraft. Failure of DO-178B Level D software could be typified by minor injuries. Approximately 20% of avionics systems and 10% of avionics software code must meet DO-178B Level D criteria.

DO-178B Level E software is software whose anomalous behavior, as shown by the system safety assessment process, would cause or contribute to a failure of system function with no effect on aircraft operational capability or pilot workload. Failure of DO-178B Level E software would have no impact on passenger or aircraft safety. Approximately 10% of avionics systems and 5% of avionics software code must meet DO-178B Level E criteria (note however that the amount of DO-178B Level E sourcecode is increasing due to passenger entertainment and internet communications subsystems that are currently designated Level E; it is deemed likely by us that the criticality levels of these systems will increase due to integration with other, more critical, avionics systems).

DO-178B tool qualification is the process whereby software development and verification tools are evaluated to determine if formal qualification is required. There are two types of qualification: DO-178B development tool qualification and DO-178B verification tool qualification. DO-178B development tools provide outputs which are actually present in the embedded operational avionics software; such tools must apply DO-178B software lifecycle aspects to ensure integrity. DO-178B verification tools are used to assist DO-178B verification. Tools which meet these criteria and which automate or replace process steps cited by DO-178B must be qualified. DO-178B Tool Qualification details are provided in our DO-178B Training courses.

RTCA/DO-178B structural coverage requirements pertain to the proof that formal software verification test cases fully covered the applicable software structures (conditions and paths). DO-178B structural coverage is not required for Level E and Level D software; it is required in increasing degrees for Level C, Level B, and Level A software. DO-178B statement coverage is required for Level C; this essentially requires each code statement to be executed by formal test cases. DO-178B decision condition coverage is required for Level B; this essentially requires each code branch to be executed by formal test cases. DO-178B modified condition decision coverage is required for Level A; this essentially requires each condition within each decision statement to be independently verified for its effect on that statement. DO-178B structural coverage is complex and is a primary cost driver on avionics project. DO-178B structural coverage tools exist from many vendors to assist in verification. Our company provides detailed DO-178B structural coverage seminars and tutorials via our DO-178B Training program.

DO-178B Certifiability is the designation of an avionics component to meet a defined subset of the DO-178B certification requirements, with the remaining certification requirements to be achieved subsequently. DO-178B certification pertains to individual systems, hence requires all software components of a system to be completed, with each component, and the system, fully meeting all DO-178B requirements. However, in the absence of a completed system, an individual software component (RTOS, graphics library, communications protocol, etc) can be designated certifiable by subjecting that component to all DO-178B requirements. Our company provides DO-178B certifiability roadmaps and DO178B certifiability kits to enable software component developers to achieve DO-178B certifiability of their products.

Military DO178 is a subset of DO-178B. Until recently, aerospace and military software standards emphasized documentation consistency rather than the modern software lifecycle attributes associated with avionics software safety (SEI CMM and CMMI). Led by the U.S. Military, there has been gradual adoption of DO-178B to emulate the commercial aviation industry. However, Military DO-178B does not require FAA and Designated Engineering Representative involvement, and certain DO-178B requirements are lessened. The resultant process is thus called DO-178B Compliance rather than DO-178B Certification. Our company provides Military DO-178B Compliance training, templates, and compliance kits.