| Design Assurance Guidance for Airborne Electronic Hardware | |
| Domain: | Aviation electronics |
RTCA DO-254 / EUROCAE ED-80, Design Assurance Guidance for Airborne Electronic Hardware is a document providing guidance for the development of airborne electronic hardware, published by RTCA, Incorporated and EUROCAE. The DO-254/ED-80 standard was formally recognized by the FAA in 2005 via AC 20-152 as a means of compliance for the design assurance of electronic hardware in airborne systems.[1] The guidance in this document is applicable, but not limited, to such electronic hardware items as
The document classifies electronic hardware items into simple or complex categories. An item is simple "if a comprehensive combination of deterministic tests and analyses appropriate to the design assurance level can ensure correct functional performance under all foreseeable operating conditions with no anomalous behavior." Conversely, a complex item is one that cannot have correct functional performance ensured by tests and analyses alone; so, assurance must be accomplished by additional means. The body of DO-254/ED-80 establishes objectives and activities for the systematic design assurance of complex electronic hardware, generally presumed to be complex custom micro-coded components, as listed above. However, simple electronic hardware is within the scope of DO-254/ED-80 and applicants propose and use the guidance in this standard to obtain certification approval of simple custom micro-coded components, especially devices that support higher level (A/B) aircraft functions.[1] [3]
The DO-254/ED-80 standard is the counterpart to the well-established software standard RTCA DO-178C/EUROCAE ED-12C. With DO-254/ED-80, the certification authorities have indicated that avionics equipment contains both hardware and software, and each is critical to safe operation of aircraft. There are five levels of compliance, A through E, which depend on the effect a failure of the hardware will have on the operation of the aircraft. Level A is the most stringent, defined as "catastrophic" effect (e.g., loss of the aircraft), while a failure of Level E hardware will not affect the safety of the aircraft. Meeting Level A compliance for complex electronic hardware requires a much higher level of verification and validation than Level E compliance.
The main regulations that must be followed are the capturing and tracking of requirements throughout the design and verification process. The following items of substantiation are required to be provided to the FAA, or the Designated Engineering Representative (DER) representing the FAA:
The hardware design and hardware verification need to be done independently. The hardware designer works to ensure the design of the hardware will meet the defined requirements. Meanwhile, the verification engineer will generate a verification plan which will allow for testing the hardware to verify that it meets all of its derived requirements.
The planning process is the first step where the design authority (the company who develops the H/W and implements the COTS into its design) declares its approach towards the certification. At this point the PHAC (Plan for H/W Aspects of Certification) is presented to the authorities (EASA, FAA...). In this plan, the developer presents its approach and how DO-254/ED-80 is implemented. The PHAC is submitted as part of the authorities 1st stage of involvement (SOI#1).It is important to note that:
For a generic DO-254 based process, a job aid is provided including the Stages of Involvement (SOIs) defined by FAA on the "Airborne Electronic Hardware Review Job Aid".
The hardware requirement validation process provides assurance that the hardware item derived requirements are correct and complete with respect to system requirements allocated to the hardware item. Validation of hardware requirements allocated from system requirements is a system process, rather than a hardware process. As such, hardware requirements that are derived by hardware processes should be identified to system processes for validation against the system requirements. For the purposes of this document's processes, a requirement is complete when all the attributes that have been defined are necessary and that all the necessary attributes have been defined, and a requirement is correct when the requirement is defined without ambiguity and there are no errors in the defined attributes.
The verification process provides assurance that the hardware item implementation meets all of the hardware requirements, including derived requirements. Methods of verification include qualitative review, quantitative analysis, and functional testing.
A widely used industry definition for the difference is:
While simple electronic hardware (SEH) is within the scope of DO-254/ED-80,[3] its guidance on the subject has been considered inadequate among applicants seeking certification of simple electronic hardware.[4] The Certification Authorities Software Team published the Position Paper CAST-30, Simple Electronic Hardware and RTCA Document DO-254 and EUROCAE Document ED-80, to provide clarification to the guidance for simple electronic hardware. This clarification was amplified as FAA guidance in FAA Order 8110.105.[5]
Essentially, for simple electronic hardware, the verification through “comprehensive combination of deterministic testing and analysis” that justifies the simple classification needs to be defined, performed, and recorded. However, the appropriate "rigor and thoroughness" of that verification depends on the hardware design assurance level. For Level A/B, test coverage analysis should confirm that all nodes and interconnections have been exercised (comparable to DO-178C structural coverage objectives), while for Level C it is only needed to demonstrate correct operation under all combinations and permutations of conditions applied only to the inputs of the device (black box), and Level D testing can be accomplished through indirect tests applied to the system that has the item installed.[4] [5]
If certification as a simple electronic device is sought, minimal documentation still should be submitted. A Plan for Hardware Aspects of Certification (PHAC) should be submitted to communicate the justification and means of certification, and a Hardware Verification Plan should be submitted to communicate the rigor and methods of the deterministic testing and analysis. Hardware Accomplishment Summary should be submitted to show compliance to the PHAC, and a Hardware Configuration Index should be submitted to define the production baseline that is the subject of the Hardware Identification and Compliance Statement in the Hardware Accomplishment Summary.[4] [5]