Recommendation #2 – Guide to the Guidelines

Recommendation 2: Publish a hierarchical guide to the guidelines document showing

interrelationships and dependencies between Advisory Circulars, FAA Orders, ARP guidelines, RTCA guidelines and key industry guidelines. During this process close the missing cross reference holes found in the various guidelines. Consideration should be given to an electronic guideline system.

Note: In an attempt to provide examples that would assist the multi-tier developer, we generated some sample hierarchical diagrams included below. These are just samples, and are not complete.

At present there is no overall top down organization of the guidelines, ACs, and Orders documents that would provide an overview of the “safety system”. Related or relevant documents can only be found by searching the references within the guidelines, orders, and advisory circulars. For example: It may take some time for a developer to stumble onto the CPI Guide, which contains valuable guidance and models for the creation of a PSP and PSCP. AC23.1309-1E calls out Order 8110. Order 8110.4C Change 5 calls out the CPI guide a number of times. However neither AC25.1309-1A nor AC23.1329-1B reference Order 8110.4C. None of the ARP documents or RTCA documents reference Order 8110.4C. So, unless the developer begins with AC23.1309-1E or stumbles onto 8110.4C he is likely to be unaware of the FAA and Industry Guide to Product Certification.

Around half of the references made are just that, references. The other half provide some meat as to why the reference is made and what the reference provides. At least they point to other sources of guidance. There are some notable reference absences:

x DO-326 not being mentioned by the ARP documents.

x The age of AC 25.1309 is showing by missing references that are found in AC 23.1309.

We could not find any existing hierarchical guideline reference documents that would guide a multi-tier supplier in understanding the safety processes. Experienced DER and Safety Specialists felt these kinds of graphics would be useful aids to them and experienced developers.

When there is difficulty in extracting requirements or guidelines, it heightens the risk that all guideline requirements will not be followed. Therefore, we have identified the deficiency in the clarity of guideline interrelationships as a critical enhancement to enable multi-tier developer understanding of regulatory guidance. Figure 12 below illustrates what might appear to the tiered developer as a forest of

documentation he must wade through, assuming he found these. Figure 12, however, is much more organized than the tiered developer will find. It already reflects a pass through documents extracting relevant referenced documents from within them.

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Figure 12. Document Forest

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The most useful existing guideline interaction diagram is “Figure 1- Guideline Documents Covering Development and In-Service/Operational Phases” found in ARP4754A, shown below in Figure 13.

Figure 13. ARP 4754A Document Interrelationship

Figure 13 is however limited to the interactions between ARP-4754A and ARP-4761A, DO-254, DO-178C, and DO-297.

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There are many more relationships to ARP-4754A as illustrated in Figure 14 below. Those in boldface include a reference to ARP-4754.

Figure 14. ARP4754A figure augmented with other documents

Figure 14 still does not capture the relationships between all the guidelines.

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Figure 15. FAR and Top Level AC Guideline Cross-references

Figure 15 provides an assessment of FAR Part 23/25, AC 23.1309-1E, AC 23.1329-1B, and AC 25.1309-1A references to guidelines and the call back or reference of those guidelines to these regulations. Also included are analysis products that were listed in these ACs and the call back from the guidelines to these same analysis products. Interrelationships between the called out guidelines are not reflected on this diagram. It must be noted that there are many more ACs and guidelines not covered by this study, which is focused on electronic avionics development in a multi-tier environment.

Though not completely clear from this kind of diagram, the ARP documents begin to emerge as primary guidance materials.

Context Interrelationship Diagram Observations:

x Both AC 23.1309-1E and AC 23.1329-1B call out AC 25.1309-1A but the converse is not true.

x AC 23.1309-1E calls out four products: FHA, PSSA, SSA, and FMEA. AC 25.1309-1A only calls out the FHA. AC 23.1329-1B does not reference any analysis products.

x AC 23.1309-1E and AC 23.1329-1B both call out ARP4754A and ARP4761. AC 25.1309-1A does not call out either of the ARP documents.

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x ARP4754A calls out all three of the AC documents as well as referencing the FAR. ARP4761 only calls out AC 25.1309-1A. (There is current activity to update 4761 to 4761A, so perhaps 4761A will reference 4754A.)

x AC 20.115C calls out both AC 23.1309-1E and AC 25.1309-1A. Itself is called out by the both the AC 23.xx documents but not the AC 25.1309-1A.

x DO-254 calls out all four analysis products: FHA, PSSA, SSA, and FMEA. DO-178C does not.

x Even though these cross references are made in these documents, the reason, purpose, or content of the reference (the flow of information) is generally missing except in the cases of the ARP documents.

Figure 16. ARP 4754 ARP4762 Guideline Cross References

Figure 16 breaks out the cross references from ARP-4754A and ARP-4761 to the advisory circulars, orders, and RTCA documents. Also included in the diagram are artifacts described in ARP-4754A and ARP-4761 that should be generated.

ARP Guideline Cross Reference Observations:

x AC 20-174 recognizes the ARP documents as an acceptable method for establishing a development assurance process.

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x Half of the advisory circulars call out the ARP documents by name only with no specific purpose or content.

x The ARP documents are consistent in their call out of artifacts.

Figure 17 below provides a hierarchical reference graphic of DO-178C, DO-254, and DO-326 from the advisory circulars, orders, ARP, and primary RTCA documents. Artifacts identified by the individual RTCA documents are included with a flow to what document gave them reference.

Figure 17. RTCA Guideline Hierarchy RTCA Guideline Hierarchy Observations:

x Some references are to specific revision numbers. Later documents are generic: XXX-() x AC 25.1309-1A stands out as missing references here as well

x DO-326 appears the most complete in its referencing x Some slight differences exist in artifact titles ex: SCM/SCMP

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