Letters to the Editor


  • Charles Hoes Hoes Engineering
  • Ted W. Yellman Boeing (retired)
  • Thomas M. Murray Acute Management Strategies, LLC




letters, safety, reliability, aviation, FAA


Software Safety vs Software Reliability

While looking back through Vol. 56, No. 1 (Summer 2020) of Journal of System Safety, I finally took the time to read Nathaniel Ozarin’s article “Lessons Learned in a Complex Software Safety Program.” The article is quite interesting and thought provoking, comparing what actually occurs while implementing a system safety program to the idealized descriptions found in documents such as MIL-STD-882, JSSSEH and AOP-52. While I found the article interesting and informative, I noted that the author consistently characterizes the “software safety problem” as a “reliability” problem, focused on finding and preventing “failures” and ensuring high “reliability.”

Some Thoughts on the Probabilistic Criteria for Ensuring Safe Airplane-System Designs

We have been employed in the risk sciences for a total of 86 years, including 62 years in reliability engineering and safety engineering positions at The Boeing Company. For many of those years, Yellman was the designated “Risk-Analysis Focal” (person) for Boeing’s 707, 727, 737 and 757 airplane models. For several decades, the United States government has published the same criteria, created by the U.S. Federal Aviation Administration (FAA), intended to ensure that the systems on large (transport-category) aircraft have been designed to be safe [Refs. 1 and 2]. But we believe that the criteria have failed to prevent certain aircraft accidents, and we think that the reasons for that should be better understood. We hope that this discussion will contribute to a better understanding by examining the part potentially played in those accidents by the FAA’s criteria that are defined probabilistically.

Author Biography

Charles Hoes, Hoes Engineering

Charles “Charlie” Hoes began his consulting business in 1984, providing system safety engineering services to defense, aerospace, semiconductor and general industry. During that time he has become a P.E. in Safety in the State of California, a Certified Safety Profession (CSP) with a specialty System Safety Practices and earned a Master of Science degree in Safety from University of Southern California. In 1988 Charlie incorporated his business under the name of “Hoes Engineering, Inc.” He has many years of experience volunteering in support of the International System Safety Society, filling many positions including past President of the Sacramento Chapter, the Virtual Chapter, and the System Safety Society. He is a past technical editor of the System Society’s journal Hazard Prevention (re-named to be the Journal of System Safety), as well as authoring an ongoing feature article of the Journal of System Safety called “TBD” where he discusses current concerns with the system safety profession.

In his new role of being semi-retired, Charlie continues to actively work with the System Safety Society as well as participating in a few “for hire” and volunteer projects that are particularly interesting, or important, for a variety of reasons. He is enjoying the ability of being a bit more selective with regard to projects that he accepts.

Letters to the Editor




How to Cite

Hoes, C., Yellman, T., & Murray, T. (2022). Letters to the Editor. Journal of System Safety, 57(2), 4–8. https://doi.org/10.56094/jss.v57i2.188