BAM Blog: obsoleted semiconductors and DO-254
Before and Aftermarket (BAM) Blog: As semiconductors become more and more complex, guaranteeing that they can still function correctly in safety-critical applications is proving increasingly difficult; and in many cases, system testing to assure correct operation under all foreseeable equipment operating conditions is often impossible. The avionics industry has recognized this problem and introduced guidelines for manufacturers to follow to overcome the testing dilemma.
These guidelines, entitled Federal Aviation Agency (FAA DO-254) in the USA, and European Organization for Civil Aviation Electronics guidance (EUROCAE ED-80) in Europe, can be useful in situations where a semiconductor is discontinued by its original manufacturer, and a suitably authorized and qualified aftermarket manufacturer is providing ongoing device support.
DO-254 and ED-80
To meet the needs of the modern aircraft industry, complex avionics systems need to be energy efficient, highly reliable, and above all, totally safe when in use. Semiconductors are the key to achieving this, but as they themselves become more complex, the task of assuring reliability and safety becomes increasingly difficult. To add to these problems, the shorter production runs of semiconductors (driven by the rapidly-changing needs of the telecommunications and PC industries), increase the burden on avionics equipment manufacturers to achieve these goals throughout the production and lifetime of use of aircraft.
To help with qualification of complex integrated circuits in avionics applications, there are industry acceptable design assurance guidance documents for airborne electronic hardware. These douments, previously described as DO-254 (US) and ED-80 (Europe), have been approved for use by the Federal Aviation Agency (FAA) and ED-80 by the European Aviation Safety Agency (EASA). The UK Ministry of Defence Aviation Authority (MAA) also recognizes and accepts use of DO-254.
These documents, (essentially the same across the different agencies), recognize that assuring the functionality of avionics hardware can no longer be achieved by testing of the equipment alone. They define the objectives that should be met in the process of designing high integrity electronic hardware for avionics applications.
The basic guideline steps in use of these documents are:
– Knowledge and understanding of the equipment’s use;
– Knowledge and understanding of the supplying semiconductor manufacturer’s capabilities;
– Designing for correct use of the semiconductors in the application;
– Validation and verification of the semiconductor’s use;
– Validating the semiconductor manufacturing process; and
– Certification agreement with the semiconductor manufacturer.
The original intention for the guidelines was to cover use of high density ASICs and FPGAs, but other complex components such as microprocessors and graphics processors, have been added since the first issue of DO-254 was published in 2000.
It can be seen from the steps required that a close working relationship with the supplying semiconductor manufacturer is essential to obtain and validate all necessary evidence and data. Recently published articles have detailed examples where this has been successfully done. Last year, the European Aviation Safety Agency (EASA) approved a Thales safety-critical avionics application containing a DO-254-certifiable version of Altera’s FPGA-based Nios II embedded processor. (Ref. Avionics Intelligence-com/articles published March 2011) This article describes the background to these guidelines, and explains how some of the initial ambiguities have been addressed by the DO-254 user groups.
Use of DO-254/ED80 to certify equipment at the design stage can be useful when the original semiconductor manufacturer decides to discontinue the device, and has authorized an aftermarket manufacturer capable of replicating in full the original device. To do this, the manufacturing, production and testing conditions have to be exactly as the original or, where small changes may be necessary, they are able to supply acceptable documentation defining those differences. This allows the equipment manufacturer and/or user to replace the original OCM part with one supplied by the aftermarket manufacturer with minimum needs for requalification.
Along with qualification and testing expertise, Rochester Electronics has authorization agreements with some 60 original semiconductor manufacturers, using IP from these manufacturers for ongoing semiconductor supply, to help meet DO-254/ED80 standards.