Harry you ask;
Does the Safety Case have to examine every possible issue and put a risk on it??
And how do we risk the "known unknowns"??
I believe that the safety case must include an a assessment of
all known and potential hazards, all of which should be managed to ALARP. Potential hazards are identified through experience and brainstorming. Just because it hasn't happened does not mean it will not happen. A fire in Dry Bay No 7 of XV230 had not happened in 35 years of Nimrod flying but it did on 2nd Sept 2006. The coroner's verdict was that the aircraft had never been airworthy.
DV