Air Force probability of detection inspection studies (1980s)

Cited as the source of the curve: 95% probability of detection at ⅛", 50% at 1/16", very low in the mm range. Used to anchor the Sea Wolf inspection-gap story.

They had to cut out every weld in the sub. Student: What testing did they usually do? Typically magnetic particle, but they're looking for large flaws. If your minimum detectable flaw size is an eighth of an inch reliably detectable — the Air Force did a bunch of studies in the 1980s on what they call probability of detection. If you plot the probability of detection by flaw size in inches, you'll be at 95% probability of detection by a manual inspection at an eighth of an inch. You'll be at about 50% at a sixteenth of an inch. These were down in the millimeter size, very low probability of detection. Aircraft engines, they're looking for things 0.015". We don't really have inspection technologies that can do it, and Boeing has specs of 0.010". No one can find it, but it's in the spec.