In 1999, Greg Lewis presented a paper to the Flight Test Society of Australia, “Flight Test Safety in Civil Certification,” in which he describes unique risks and incidents that occurred during civil certification flight test with government test pilots. One of the interesting facts in the paper is the first known reference (I think)–in a technical paper–to the FAA’s Order 4040.26. For some of us, it seems like the order always existed, but this paper reminds us that FAA’s test safety guidance is relatively young, at least in its current form. The other thing the paper describes is several flight test aircraft incidents. The ability to recall incidents like this is important for flight test professionals, because it informs our intuition about the likelihood of the hazards we are assessing. It gives us data by which to assess the confidence of our probability estimates. Or does it?

That is the question addressed herein — how confident are we?

The question may cause some to sweat, bringing memories of Comprehensive Oral exams at TPS or flashback of basic stats class from college, but the heuristics proposed herein should reduce the anxiety of the reader. These rules will enable us, as a flight test community, to communicate about uncertainty even as we face more in the years to come.

One last thing about Greg’s paper: it’s an excellent resource, and the FTSA recently generously shared it with members of our community. So get your hands on a copy and thank your colleagues down under

Finally, please continue to share this newsletter. Let us know when you do, because we want to Reach Everyone (117%). Send questions and comments to or any FTSC member.

Download Flight Test Safety Fact, 19-09.

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