This document answers some Frequently Asked Questions (FAQs) about the certification of computer software for avionics. The answers to the questions are not intended to provide a definitive technical answer but rather to inform the reader in a general manner.
SAFETY AGENCIES
SAFETY CERTIFICATION STANDARDS
Q. Who developed the DO-178/ED-12B spec?
Q. What does DO-178B/ED-12B specify?
Q. In a nutshell, what does this DO-178B specification really do?
Q. To what do DO-178B levels refer?
Q. Who determines which DO-178B level is required?
Q. What is the total list of potential deliverables I will need to create for DO-178B certification?
Q. Which systems need to be certified under DO-178B?
Q. What levels of structural testing are required by DO-178B?
Q. How is a software verification performed?
Validated Software Corporation’s Validation Suite
Q. What are Validated’s Validation Suites?
Q. What comprises a Validation Suite?
Q. Is the Validation Suite a special version of the product code?
Q. Can the Validation Suite be reused on new projects?
Q. How do I order the Validation Suite?
Answers
SAFETY AGENCIES
RTCA, in the avionics sense (to which all references in this document refer) is the acronym for Radio Technical Commission for Aeronautics. RTCA, Inc. is located at:
1828 L Street, NW, Suite 805
Washington, D.C. 20036
Tel: 202-833-9339
Fax: 202-833-9434
RTCA’s web site is: www.rtca.org/
EUROCAE is the acronym for the European Organisation for Civil Aviation Equipment. It is the European equivalent of RTCA. EUROCAE is located at:
17 Rue Hamelin
75116 Paris
FRANCE
Tel: +33 (0) 1 4505 7188
Fax: +33 (0) 1 4505 7230
EUROCAE’s web site is: www.eurocae.org
FAA is the acronym of the U. S. Federal Aviation Administration, the organization responsible for controlling air traffic safety in the United States.
The FAA's web site is: www.faa.gov
JAA is the acronym for the Joint Aviation Authorities in Europe. The JAA is an associated body of the European Civil Aviation Conference (ECAC) representing the civil aviation regulatory authorities of a number of European states that have agreed to cooperate in developing and implementing common safety regulatory standards and procedures. The JAA and the FAA work together to create complementary air traffic safety standards. The JAA is located at:
Saturnusstraat 8-10,
PO Box 3000
2130 KA Hoofddorp
The Netherlands
Fax: +31 (0) 23-5621714
The JAA’s web site is: www.jaa.nl/
SAFETY CERTIFICATION STANDARDS
DO-178, is a set of avionics standards described in the RTCA Document RTCA/DO-178, titled “Software Considerations in Airborne Systems and Equipment Certification,” was developed by the avionics industry to establish software considerations for developers, installers, and users, when aircraft equipment design is implemented using microcomputer techniques.
The first formal publication of this specification was published in 1982 by the Radio Technical Commission for Aeronautics (RTCA). This was also approved by EUROCAE as ED-12 shortly thereafter.
An update to DO-178 was published in 1985, and was called DO-178A. EUROCAE also published an matching update to ED-12, named ED-12A.
In 1992, various industry working groups published a comprehensive update to DO-178A, named DO-178B by RTCA and ED-12B by EUROCAE. This revision of DO-178B is the current working version of this specification.
RTCA Document RTCA/DO-178B, titled “Software Considerations in Airborne Systems and Equipment Certification,” was developed by the avionics industry to establish software considerations for developers, installers, and users, when aircraft equipment design is implemented using microcomputer techniques. Note that DO-178B/ED-12B projects must be certified as a system, not a standalone component, as for IEC-61508 software components.
This document is an update of ED-12A, published in 1985. It is the EUROCAE version of DO-178B. See DO-178B, above.
RTCA DO-248B is a clarification document to DO-178B. Major topics include Previously Developed Software (PDS), Commercial Off-the-Shelf (COTS) software, verification, service history, tools and control categories. RTCA DO-248B is available from RTCA.
AC20-RSC is a notice published by the FAA that defines guidelines to DERs for approving software reused from previous DO-178B projects. All software life cycle data used in DO-178B certified systems require design approval under Title14, Code of Federal Regulations (14 CFR).
Q. Who developed the DO-178B/ED-12B spec?
DO-178B and ED-12B were developed by a broad committee of industry representatives from around the world. These specifications are published by RTCA, Inc. and EUROCAE, respectively.
Q. What does DO-178B/ED-12B specify?
DO-178B/ED-12B provides guidance on designing, specifying, developing, testing, and deploying software in safety-critical avionics systems. In sum, DO-178B is a guideline for determining, in a consistent manner and with an acceptable level of confidence, that the software aspects of airborne systems and equipment comply with FAA airworthiness requirements.
Q. In a nutshell, what does this DO-178B specification really do?
It specifies that every line of code be directly traceable to a requirement and a test routine, and that no extraneous code outside of this process be included in the build.
Q. To what do DO-178B levels refer?
DO-178B software levels (A, B, etc.) are based on the potential of the software to cause safety-related failures identified in the system safety assessment. DO-178B has five levels of certification:
Level A: Software whose failure would cause or contribute to a catastrophic failure of the aircraft.
Level B: Software whose failure would cause or contribute to a hazardous/severe failure condition.
Level C: Software whose failure would cause or contribute to a major failure condition.
Level D: Software whose failure would cause or contribute to a minor failure condition.
Level E: Software whose failure would have no effect on the aircraft or on pilot workload.
Q. Who determines which DO-178B level is required?
The level to which a particular system must be certified is selected by a process of failure analysis and input from the device manufacturers and the certifying authority (FAA or JAA), with the final decision made by the certifying authority. Note that software does not need to be certified specifically at each designated level. Certification at any level automatically covers the lower-level requirement; but, obviously, the converse is not true. Software certified at Level A can be used in any avionics application.
Q. What is the total list of potential deliverables I will need to create for DO-178B certification?
The following table lists the documents and records you may need to provide for a DO-178B certification:
DO-178B Software Life Cycle Data List
Document Title
Type
Section
PSAC
Plan for Software Aspects of Certification
Document
11.1
SDP
Software Development Plan
Document
11.2
SVP
Software Verification Plan
Document
11.3
SCMP
Software Configuration Management Plan
Document
11.4
SQAP
Software Quality Assurance Plan
Document
11.5
SRS
Software Requirements Standards
Document
11.6
SDS
Software Design Standards
Document
11.7
SCS
Software Code Standards
Document
11.8
SRD
Software Requirements Data
Document
11.9
SDD
Software Design Description
Document
11.10
Source Code
Software
11.11
Executable Object Code
Software
11.12
SVCP
Software Verification Cases and Procedures
Document
11.13
SVR
Software Verification Results
Records
11.14
SECI
Software Life Cycle Environment Configuration Index
Document
11.15
SCI
Software Configuration Index
Document
11.16
PRs
Problem Reports
Records
11.17
Software Configuration Management Records
Records
11.18
Software Quality Assurance Records
Records
11.19
SAS
Software Accomplishment Summary
Document
11.20
DERs, Designated Engineering Representatives, are experienced engineers designated by the FAA to approve engineering data used for certification. Most customers (and the FAA) will want some assurance in your DO-178B documents, and an FAA DER will provide this. All FAA projects must have an FAA representative assigned and a DER to review all submissions. A DER is an independent specialist designated by the FAA as having authority to sign off on your project as a representative of the FAA. First, the DER may insist on witnessing such items as portions of your software testing; second, the DER may not like your documentation (or processes), hence may insist on changes to them before signoff. This is a lot easier to do during design and development than at project completion.
Q. Which systems need to be certified under DO-178B?
Under the Global Aviation Traffic Management (GATM) agreement, all commercial airborne systems have to comply with Federal Aviation Administration (FAA) regulations for avionics and require DO-178B certification. In addition, all airborne military and space systems must also comply with DO-178B. All retrofits, as well as new airborne system designs, also require DO-178B certification. Note that GATM has international validity and applicability.
Q. What levels of structural testing are required by DO-178B?
Three primary levels of structural testing concern most DO-178B projects:
SC: Statement Coverage. Means that every statement in the program has been invoked or used at least once. This is the most common use of the term “code coverage.”
DC: Decision Coverage. Means that every point of entry and exit in the program has been invoked at least once and that each decision in the program has been taken on all possible (Boolean) outcomes at least once. Essentially, this means that every Boolean statement has been evaluated both TRUE and FALSE.
MCDC: Modified Condition Decision Coverage. Means that every point of entry and exit in the program has been invoked at least once, that every decision in the program has taken all possible outcomes at least once, and that each condition in a decision has been shown to independently affect that decision's outcome. Complex Booleans need to have truth tables developed to set each variable (inside a Boolean expression) to both TRUE and FALSE.
This table details the code coverage requirements for each DO-178B level:
Level
Coverage
Explanation
Level A
MCDC
Level B + 100% Modified Condition Decision Coverage
Level B
DC
Level C + 100% Decision Coverage
Level C
SC
Level D + 100% Statement (or Line) Coverage
Level D
100% Requirements Coverage Requirements
Level E
No Coverage Requirements
Performing this code coverage exercise is possible using manual methods, but this process is now readily facilitated by implementing commercial code coverage tools. See Code Coverage Tools page for a list of known vendors in this space.
Q. How is a software verification performed?
DO-178B/ED-12B defines specific verification objectives that must be satisfied; these include:
Verification of software development processes
Review of software development life cycle artifacts
Functional Verification of software
a. Requirements-based testing and analysis
b. Robustness testing
Structural Coverage Analysis
Structural Coverage Analysis is generally perceived to be the most difficult task to undertake by people unfamiliar with rigorous code development and testing. Furthermore, an operating system is tightly integrated with the hardware, cache, interrupts, memory management, and process/task management, thereby making structural testing even more difficult. These low-level aspects create a significant challenge to the verification process. For example, Level A certified applications must address:
Statement Coverage
Decision Coverage
Modified Condition/Decision Coverage (MCDC)
and from the code coverage table above along with:
Identification of dead or deactivated code
Traceability from source to object code
Fortunately, a variety of commercial tools are available to assist in this challenging task.
See our Code Coverage Tools page for a list of known vendors in this space.
Validated Software Corporation’s Validation Suite™
Q. What are Validated’s Validation
Suites?
Validated’s Validation Suites are packages of standards, plans, requirements, designs, and tests to address manufacturers requiring safety certification documentation for projects. Validation Suites are typically developed for software products widely used in safety-critical products. The use of our Validation Suites allows developers to concentrate on their core product and lower their costs by purchasing an essentially off-the-shelf Validation Suite as a component.
Q. What comprises a Validation Suite?
Due to different DO-178B requirements for different certification levels, the amount of documentation will differ, but, in general, the following documentation will be provided in Level A through Level C Validation Suites.
Validation Suite Component
DO-178B Item
Plan for Software Aspects of Certification (PSAC)
11.1
Software Development Plan (SDP)
11.2
Software Verification Plan (SVP)
11.3
Software Configuration Management Plan (SCMP)
11.4
Software Quality Assurance Plan
11.5
Software Requirements Standard
11.6
Software Design Standard
11.7
C Language Coding Standard
11.8
Software Requirements Document (SRD)
11.9
Microprocessor Port Requirements and Design Documents
11.9
Software Design Document
11.10
Software Source Code, Test Code and Build Code
11.11
Software Port Image
11.12
Software Unit Test Plans and Procedures
11.13
Software Integration Test Plans and Procedures
11.13
Software Unit Test Reports
11.14
Software Integration Test Report
11.14
Software Test Coverage Report
11.14
Software Life Cycle Environment Configuration Index
11.15
Software Configuration Index
11.16
Software Problem Report History
11.17
Software Change History
11.18
Software Quality Assurance Data
11.19
Software Accomplishment Summary (SAS)
11.20
In addition, Validated also offers port-specific documentation to provide all the board support package (BSP) documentation, for example:
Port Software Design Description, Special I/O
Port Software Design Description, Special 80x86 Protected Mode Port
Q. Do I also have to pay the manufacturer for a production license when I purchase Validated’s Validation Suite?
Yes. The Validated Suite does not include a production license for the software.
Yes. The Validation Suite contains all source code to the product and all source code to test files, all test scripts, and all build/make files. Please note however that all of the products we validate are licensed by another manufacturer. As such we can not ship source code to a product until we receive confirmation from the manufacturer that you have a valid license in place with them.
Q. Is the Validation Suite a special version of the manufactures product code?
No. The source code we provide is functionally identical to the manufacturers original code. In some cases the code may belong to a "safety-critical" version of the manufacturers product, but this is the exception not the rule.
Q. Can the Validation Suite be reused on new projects?
Yes. Depending upon the system changes between projects, the Validation Suite can be used for multiple projects. FAA projects should refer to DO-248B, FAA Notice 8110.97, and their DERs for full compliance when reusing life cycle data and artifacts on multiple projects. (Note that additional license fees for both the software product and the Validation Suite may apply, regardless of re-use.) Contact Validated Software sales for further information.
MicroC/OS-II was chosen for many reasons:
MicroC/OS-II is a very stable operating system that has been used in tens of thousands of systems and hundreds of commercial applications. It has been in use for over 10 years, with minor modifications made periodically.
MicroC/OS-II has been “open source” since its creation. Therefore, it has been reviewed by thousands of individuals. But, unlike some open source projects, revisions are tightly controlled and reviewed by Micrium, and then openly reviewed by the MicroC/OS-II community.
MicroC/OS-II was written against a very strict coding standard, which improves readability, understandability, and maintainability – all key aspects of creating software used in critical systems.
Every line of MicroC/OS-II is well documented. This is extremely rare in the software industry and is ideal for safety certification where the mapping of requirements to source code to test for every line of code is required.
Q. How do I order the Validation Suite?
All Validated Software products can be ordered from the Validated Software Sales office.