January 05, 2024

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Sofema Aviation Services (SAS) www.sassofia.com considers the role and purpose of Society of Automotive Engineers (SAE) Aerospace Recommended Practice – ARP 4761 and ARP 4754A

Introduction

Aerospace Recommended Practices ARP 4761 and ARP 4754A are two crucial guidelines in the aviation industry, issued by the Society of Automotive Engineers (SAE).

ARP 4754A and ARP 4761 emerged from the need to improve safety and reliability in the aviation industry. As aircraft systems became more complex, traditional design and testing methods were insufficient to assure safety and reliability.

The purpose of these standards is to help achieve the best safety practices in the aviation industry. The application of these practices has become a fundamental requirement in aircraft design, and non-compliance can lead to significant safety risks and regulatory issues. Therefore, any organization involved in the design, manufacture, and operation of aircraft must familiarize itself with these standards.

ARP 4761 – Aerospace Recommended Practices & ARP 4754A Guidelines For Development Of Civil Aircraft and Systems, forms the foundation of a development process which is designed to discover all conditions that could potentially affect the safety of an aircraft and its occupants and to provide all the necessary information to manage these conditions.

In practical terms, the guidelines from ARP 4761 are followed from the early stages of design, when the initial concept is being developed, throughout the product’s lifecycle. The safety assessment process is iterative and needs to be reevaluated whenever there are changes to the system design or operating conditions.

The output of the ARP 4761 process, typically the SSA, is a significant piece of evidence presented for certification and forms part of the safety case for the aircraft. This ensures that safety is not just an afterthought, but an integral part of the design process.

Considering ARP 4761

ARP 4761, titled “Guidelines and Methods for Conducting the Safety Assessment Process on Civil Airborne Systems and Equipment,” Was developed to enable a uniform and systematic approach to identifying, analyzing, assessing, and documenting hazards and their associated risks in aerospace systems and provides a set of guidelines for conducting safety assessments on civil airborne systems and equipment.

  • Originally published in December 1996 in response to an increasing reliance on complex systems in aviation and the necessity of formalizing safety assessment procedures.

Note – Before its publication, there wasn’t a comprehensive standard for conducting safety assessments.

  • The role of ARP 4761 is to provide systematic methods to identify and analyze potential hazards and to assess and mitigate associated risks in civil airborne systems and equipment.
  • It provides guidelines for the entire safety assessment process, which includes:
    – Functional hazard assessment (FHA),
    – Preliminary system safety assessment (PSSA), and
    – System safety assessment (SSA).
  • The ARP 4761 process begins with an FHA to identify potential system failures that could result in hazardous conditions.
  • This is followed by a PSSA, where the proposed system design is analyzed to determine if it can adequately mitigate the hazards identified in the FHA.
  • Finally, the SSA verifies that the design and implementation of the system meet the safety objectives and requirements.

Note – ARP 4761 also includes specific safety analysis techniques such as

  • Fault Tree Analysis (FTA),
  • Failure Modes and Effects Analysis (FMEA), and
  • Common Cause Analysis (CCA).

Integration into Aircraft Design Obligations

ARP 4761 is often integrated into aircraft design through the certification process.

  • The certifying authorities like the Federal Aviation Administration (FAA) in the U.S. or the European Union Aviation Safety Agency (EASA) in Europe, require aircraft manufacturers to provide evidence of compliance with their safety regulations.
  • They usually recommend, and in some cases require, the use of ARP 4761 as a means to achieve this.

Considering ARP 4754A

ARP 4754 was first issued in 1996 to address these challenges by standardizing the system development process. The standard was revised in 2010 (ARP 4754A) to further improve the development process.

ARP 4754 provides a common language and set of practices that allow different stakeholders (manufacturers, regulators, suppliers, etc.) to communicate and cooperate effectively in the development of an aircraft.

  • Following the ARP 4754 process is often seen as a way to demonstrate compliance with the airworthiness regulations to certify the aircraft for flight.

ARP 4754A, also known as “Guidelines For Development Of Civil Aircraft and Systems”, is a standard that guides applying systems engineering to the development of aircraft systems.

  • The document emphasizes the importance of a structured, disciplined, and documented approach to ensure the aircraft’s safety, functionality, and integrity.

Integration into Aircraft Design Obligations

ARP 4754A is generally applied first, as it guides the aircraft and systems development process.

  • The document encourages a system engineering approach, which means considering the aircraft and its systems holistically rather than as separate entities.
  • It also emphasizes the verification and validation processes to ensure that the system meets the defined requirements.

Once the system architecture is defined based on ARP 4754, ARP 4761 comes into play. The safety assessment processes in ARP 4761, like Fault Tree Analysis (FTA) and Failure Modes and Effects Analysis (FMEA), are applied to each system.

  • These analyses identify and classify potential failure conditions and their effects, helping engineers devise strategies to mitigate risks.
  • The results of the safety assessments (ARP 4761) are then used to adjust the aircraft’s design and operations to meet safety requirements.
  • The process starts with capturing requirements and defining the system.
  • Next, an initial system architecture is proposed, and its safety is assessed through functional hazard assessments and preliminary system safety assessments. This helps to identify any potential failure conditions and their classification.
  • After the system design is finalized, it moves into the development stage where the hardware and software are built. Each component is verified to meet its specific requirements and the overall system requirements.
  • The subsystems and systems are then integrated and validated to ensure they function as expected in the aircraft environment.
  • Finally, the developed system goes through certification with aviation regulatory bodies. After certification, the system continues to be assessed throughout its operational life for any potential safety issues that may arise.

Note – The process may be iterative, with safety assessments feeding back into system design adjustments as necessary until the design is final and complies with all safety objectives.

Next Steps

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Sofema Aviation Services (www.sassofia.com) covers training relevant to this topic – check it out here: CS 25 System Safety Assessments

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SAS blogs, SAE, System Safety Assessment (SSA), Common Cause Analysis (CCA), Failure Mode and Effects Analysis (FMEA), Fault Tree Analysis (FTA), ARP 4761, ARP 4754A, Aerospace Recommended Practice, Functional Hazard Assessment (FHA), Preliminary System Safety Assessment (PSSA)