Still, are you completely sure that he would not be strictly liable were he to be a P.E.?
The point you're trying to make is sound. American law does hold certain occupations to a higher standard, such as medicine. Medical negligence is its own specialized field. However, I am not aware that an exception applies for engineers the way it does for medicine. I'm not aware of any engineer being held liable for defects in the aviation industry. I think the point you raise is interesting in a theoretical sense; I don't think it applies to this specific case, however.