The new ARP4761A “Aerospace Recommended Practice” is now released and soon mandatory for all civil passenger aircraft. But what is ARP4761A? Is it also used for non-civil aviation? How does it differ from its predecessor ARP4761?
ARP4761A (formally issued in 2023) has an official title “Guidelines and Methods for Conducting the Safety Assessment Process on Civil Airborne Systems and Equipment”. But in reality, ARP4761A is virtually a tutorial on aviation and aircraft safety assessments and how to apply a diverse set of technical aircraft and system analysis to define risks, hazards, and assess aircraft and system (avionics) development activities to maximize aircraft safety.
The new ARP4761A is tightly coupled with ARP4754AB and provides a formal systems engineering framework for the most necessary requirement for civil aircraft regulations: Safety. ARP4761A and ARP4754B define aircraft and aviation domains governed by safety-related regulations which include the following key aviation aspects:
- Aircraft pilots and crew
- Ground operators
- Maintenance personnel
- Air traffic control, communications, navigation
- Systems, hardware and software development including airborne and ground-based
- Aviation engineering development/verification tools including mechanical, hardware, and software
- Most aspects of aircraft manufacturing
- Flight testing
- Suppliers, manufacturing, and system/aircraft updates
ARP4761A requires a formal safety planning process which yields the following engineering activities with associated documentation which are then verified to ensure completeness:
- Aircraft Functional Hazard Assessment (FHA)
- Aircraft Fault Tree Analyses (FTAs)
- System FHAs
- System FTAs
- System Failure Modes and Effects Analyses (FMEAs)
- Item FTAs
- Item FMEAs
The safety assessment process has fundamental importance in establishing appropriate safety objectives for the aircraft and systems. The level of safety assessment activities is dependent on the aircraft level failure condition classification and the complexity of the system integration and implementation. Therefore, the safety assessment process should be planned early in the development process and managed through this process.
During the PSSA process while assessing the system architecture, if the FTA shows that the system does not meet the safety requirements (i.e., the calculated probability of the undesired top event is greater than the allowed probability), there are several key upgrades that the system manufacturer can do to improve the situation:
- Use components that have lower failure rates
- Improve Built-In-Test to detect a higher percentage of failures
- Increase the degree of redundancy in the system
For more completed details on ARP4761A the best-selling book “Aviation Development Ecosystem” by the leading industry aviation safety expert Vance Hilderman is available from major bookstores such as Amazon.