ARP4754A Introduction – Avionics Systems

ARP4754A Introduction – Avionics Systems

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ARP4754A is officially titled “Guidelines for Development of Civil Aircraft And Systems”. Rarely can one judge a book by its cover or title; however, in this case, the title literally conveys a powerful message: if you are involved with development of aircraft or systems, you should be well versed in ARP4754A’s ‘guidelines’. Why? There are two key reasons which should be understood before first opening the pages of ARP4754A:
1. ARP4754A’s title states “guidelines”, but failure to understand and apply ARP4754A will greatly reduce safety and your ability to achieve certification.
2. Where its predecessor ARP4754 was largely similar, too many organizations treated it as “optional” befitting its name “Guideline”; but certification organizations worldwide have formally mandated adherence to this latest version, ARP4754A.

For experienced, proficient developers of aircraft and systems, ARP4754A reads like a book for maintaining good personal health: make a plan for health, understand healthy living, be safe, eat well, reduce stress, exercise, sleep, get regular check-ups, and repeat. For aircraft, an analogous synopsis of ARP4754A would state:
1. Plan your aircraft/system’s development lifecycle ecosystem;
2. Implement Safety activities per ARP4761/A;
3. Define and justify Assurance Level;
4. Define System architecture and requirements; Validate.
5. Perform Verification and Configuration Management
6. Implement Quality Assurance and prove Transition Criteria.

The original ARP4754 standard was first published in 1996 with the purpose of assisting avionics development organizations to think beyond mere hardware and software. Remember, DO-178 (and its European equivalent ED-12) was published over a decade prior to provide guidelines for avionics software.  But by the early 90’s it was clear that safe software, and software certification itself, required both knowledge of the system and confirmation of system level safety aspects.  ARP4754 was focused upon aircraft systems whose failure could potentially affect safety of aircraft or occupants.  While there are certainly critical stand-alone components on aircraft which could affect safety, ARP4754 is focused not upon components, but rather systems which have complex interactions with other systems on or off the aircraft.  These systems typically involve multiple knowledge domains and are likely to evolve over time. Thus they are developed by different persons via different disciplines often separated by space and time; the best means to ensure safe implementation is via codified development processes based upon deterministic safety:  ARP4754.

ARP4754A versus ARP4754

With revision “A” of ARP4754, e.g. ARP4754A, several key improvements were made as shown below:

ARP4754A requires ARP4754A Planning, ARP4754A Processes, ARP4754A Reviews, and ARP4754A Process  Assurance (quality assurance) Audits.  Here is an all-too-brief summary of ARP4754A Plans, ARP4754A Procedures, ARP4754A Reviews, and ARP4754A Audits for avionics systems:

  • ✓ ARP4754A “Plans” comply with safety requirements and summarize what you will do, while
  • ✓ ARP4754A “Processes” state how you will implement the Plans, and
  • ✓ ARP4754A “Reviews” (with Checklists advised) denote objective review criteria to determine if Processes were followed, then
  • ✓ ARP4754A “Process Assurance  Audits” assess conformance of engineering/manufacturing activities, including respective transitions to those Processes and Reviews.

The following page is reprinted from AFuzion’s 300-page proprietary ARP4754A Training manual (page 37 of 293 pages):

ARP4754A’s Eight Planning Topics

Figuratively and literally, systems development via ARP4754A is the centerpiece: it is preceded by, and must consider, the ARP4761A safety assessment which is used to help define system architecture and system safety requirements. (See AFuzion’s ARP476! Whitepaper for safety details; free download here: https://afuzion.com/rp-4761a-introduction-avionics-safety/ ) In turn, ARP4754A precedes software (DO-178C) and hardware (hardware) development yet aircraft and system considerations are continuously addressed during the entire software and hardware development. A refined view of the relevant guidelines showing ARP4754A’s importance is depicted here:

Why ARP4754A? Background.

Before delving into ARP4754A specifics, one should truly consider why it exists. When avionics systems were simpler decades ago, it was possible for smart designers to avoid a framework posed by ARP4754A and simply mentally conceive those systems and proceed immediately with implementation. Admittedly today, the need for ARP4754A is less justifiable for simple systems, but such simple systems are becoming fewer and fewer. But for modern aircraft, the number, variety, and complexity of systems continues to grow exponentially. Clearly, avionics systems can be much more complex than commercial brick and mortar buildings, but it would be inconceivable to begin building a commercial office building without a soil/earthquake analysis, foundation design, and a plan for inspections. Those inspections obviously continue throughout the building process including satisfactory electrical, plumbing, emergency exits, and proper reinforcement. While it is possible great builders could possibly build a safe building without detailed plans, blueprints, processes, and inspections, there would be no way to fully verify the building’s “greatness.” Why? “Greatness” must be associated with proof a building is great. Proof is based upon assessing implementation versus plans then correcting any deficiencies found. ARP4754A is aviation’s framework for proving reliable, safe, and reusable aircraft and systems. Clearly, without plans and processes for a building, there is no way to assess, or claim, a building’s design and construction are safe. Since developing avionics can be more complex than constructing a building,it is clear that avionics systems require big-picture planning, processes, requirements, safe development, verification/validation, and evidentiary proof of conformance. Welcome to ARP4754A, “Guidelines for Development of Civil Aircraft And Systems.”

With revision “A”, e.g. ARP4754A, several key improvements were made as shown below:

ARP4754 was “good”: it described a foundational process for developing safe, good-quality avionics systems and aircraft. However, due to the evolution of related guidelines and certification refinement, and a requirement to address increasing integration and complexity of systems, ARP4754 was considered by many to be incomplete; thus, ARP4754A was not applied as rigorously as needed.

By contrast, ARP4754A truly emphasizes the importance of an entire ecosystem for avionics system development, founded upon a formal Safety process (supported by ARP4761). ARP4754A provides specific guidance to complying with regulations, and instructions into a “how to” guide for aircraft and system development, emphasizing the need to integrate that Safety and Systems process continuously throughout development. (Note while ARP4754A can be perused in a day, understanding it requires formal training; AFuzion’s 2-Day private customized ARP4754A training has been provided to over 100 organizations and 3,000 engineers. Information on AFuzion’s ARP4754A Training Classes is here: https://afuzion.com/private-training/avionics-systems-arp-4754a-training-class/).

The ARP4754A aviation development ecosystem covers numerous ARP and DO documents as depicted in the following figure:

Figure: ARP4754A & ARP4761A Aviation Ecosystem

 

Figuratively and literally, systems development via ARP4754A is the centerpiece:  it is preceded by, and must consider, the ARP4761A safety assessment which is used to help define aircraft/system architecture, and aircraft/system safety requirements.  In turn, ARP4754A precedes software and hardware development, yet system considerations are continuously addressed during the entire software and hardware development associated with ARP4754A.    For a free 1-hour ARP4754A training video, see here: https://www.youtube.com/watch?v=tng3rGW-BcQ&list=PL0es63yi1vbw9Tt1GWX8TtiFm4R2qRryu&index=6

 

ARP4754A versus ARP4754

With revision “A”, e.g. ARP4754A, several key improvements were made as shown below:

The scope of ARP4754A’s planning process is summarized in the following graphic:

 

At the aircraft level, ARP4754A requires an overall Safety Program Plan (SPP).  It is common to have system-level SPP’s for each system. Like building a house, the scope of ARP4754A’s aircraft and avionics safety takes many different forms: foundation, architecture, problem detection, problem mitigation, susceptibility to particular hazards (lightning, etc.), and verifiability.  So multiple ARP4754A / ARP4761A safety activities and analysis are required.  Aviation development tools are often used to perform the ARP4754A activities and ARP4761A safety assessment; the following site describes a wide selection of aircraft and avionics development tools:  http://certegic.com/aviation-development-information/adi-development-tools/   The following figure summarizes the primary safety activities necessary for ARP4754A compliance:

Primary Aircraft & Avionics Safety Activities per ARP4754A & ARP4761A

 

For a more complete description of the ARP4754A Aircraft and System Functional Hazard Assessment (FHA), PSSA, SSA and CCA, see the corresponding AFuzion ARP4761A Safety Assessment whitepaper.

The overall ARP4761A Safety process relationship within ARP4754A is depicted below:

Figure:  ARP4754A V-Model Aircraft & Avionics Engineering Lifecycle

 

ARP4754A is a complex and varied field.  For ARP4754A training and ARP4761A training, see here: https://afuzion.com/private-training/avionics-systems-arp-4754a-training-class/

Most aviation developers find their initial ARP4754A implementation cost increase to be 20-30% over conventional non-ARP4754A development.  My adopting the following ten Best Practices for ARP4754A, new users are usually able to mitigate such costs (download the rest of this free AFuzion ARP4754A Introduction whitepaper to read further).

For the remaining 13 pages of this AFuzion ARP4754A Technical Whitepaper, please download below.

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