4754, 4761 … Magic Numbers or Real Answers?

24 Apr


4754, 4761 … Magic Numbers or Real Answers?

Safety does not rely upon magic numbers but rather real answers.  Likewise, Safety is never an accident, but true Safety should prevent accidents.  The numbers “4754” and “4761” are not magic but are associated with Safety.  Safety and the Numbers have evolved – the new answers for Safety are found in 4754A and 4761A; specifically SAE’s ARP-4754A and ARP-4761A.

The Old Days …

In technology, the Old Days refer to any time prior to last year.  In the Very Old Days (moon landings, space shuttles, commercial jets with four engines) safety was addressed by brains and refinement: smart engineers did their best to prevent accidents then refinement was applied when those best efforts were less than perfect. In the Very Old days, computing horsepower was thinner, schedules were fatter, and acceptable safety generally ensued: space shuttles had a 98.5% chance of not exploding and commercial aircraft had fatal crashes “only” a few times annually. Then the very old days gave way to mere old days, and the very old ways didn’t work as well.  Some said the engineers were not as smart while others said those engineers were trying to make the computers too smart. But all agreed that more formalized safety was needed and the Society of Automotive Engineers (SAE) had been handling Aerospace Recommended Practices (ARP’s) for decades.  SAE ARP-4754, Guidelines for Development of Civil Aircraft and Systems, was published in November, 1996.  Its tightly-coupled sibling ARP-4761, Guidelines and Methods for Conducting the Safety Assessment Process on Civil Airborne Systems and Equipment, was published the next month, December, 1996.

Today & Tomorrow.

Next year in 2018, the long-awaited update, ARP4761A, will be released.  With this update, the ARP4754A & ARP4761A duopoly will be complete:  worldwide aviation will require cohesive application of formalized safety principles to avionics, aircraft, and most things in between.

ARP4754A requires aviation developers to consider, plan, and assess the following aspects of their lifecycle (see the whitepaper referenced below, for images; free download of whitepaper).

ARP4761 recognizes that safe aviation development requires the following documentation typically accompany the various analyses:

 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 world of “safety” has its own language and lexicon. Experienced safety engineers are well versed in this language, but you are probably not reading these words if you are an experienced avionics safety engineer.  To begin, please ponder the following words and test yourself by verbalizing a 1-2 sentence definition for each word (answers follow, but please spend just a few minutes pondering these words yourself before looking at the answer. Remember, you didn’t learn to drive a car by simply reading the user manual:  the real learning came when you practiced driving):

  • Adverse Effect?
  • Assessment?
  • Average probability per flight hour?
  • Complex System?
  • Design Assurance Level?
  • Extremely remote failure condition?
  • Extremely improbable failure condition?
  • Failure condition?
    • Minor?
    • Major?
    • Hazardous?
    • Catastrophic?
  • Functional hazard assessment?
  • Hazard?
  • Primary Function?
  • Primary System?
  • Reliability?
  • Secondary System?
  • Simple System?
  • System?

OK, you’ve pondered the above words.  What is their meaning when applied to avionics and aviation safety?  First, there is no mandatory definition which everyone in the world adheres to or must follow.  If you were to examine the dozen most common sources of aviation terminology, you would discover numerous minor differences within definitions of these terms—and some of the differences are not so minor.  The various authorities and authors try to maintain consistency; in aviation this is called “harmonization”, such as when the USA’s FAA and Europe’s EASA coordinate to resolve differences.  But your world is the real world, and that world is constantly evolving with an ever-expanding lexicon.  What are the above meanings and how are they used to implement safety per ARP4754A and ARP4761A?  The AFuzion whitepaper “Understanding ARP4761A”  provides the answers; free download here: AFuzion’s Free ARP4761A Introduction Whitepaper

For information on AFuzion’s ARP4754A Training and ARP4761A Training by Ms Nazan Gozay Gurbuz (SAE ARP4761A Committee Member), see here:  AFuzion’s ARP-4754A Training and ARP-4761A Training Info

For information on AFuzion’s ARP4754A Gap Analysis, see here:  ARP4754A Gap Analysis & ARP4761A Gap Analysis

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