The context is a long string of nuclear incidents throughout the Cold War through to the ‘90s.
Not just Chernobyl, not just Fukushima, but the string of disasters at Windscale / Sellafield and many others across the globe.
https://en.wikipedia.org/wiki/List_of_nuclear_power_accident...
https://en.wikipedia.org/wiki/List_of_nuclear_and_radiation_...
These disasters were huge, newsworthy and alarmingly regular. People read about those getting sick and dying directly as a result. They felt the cleanup costs as taxpayers. They saw how land became unusable after a large event, and, especially terrifying for those who had lived as adults through Cold War, saw the radioactive fallout blown across international borders by the wind.
It’s not Greenpeace or an anti-nuclear lobby who caused the widespread public reaction to nuclear. It was the public reaction seeing it with their own eyes, and making an understandable decision that they didn’t like the risks.
Chernobyl was one hammer blow to the coffin lid, Fukushima the second, but nuclear power was already half-dead before either of those events, kept alive only by unpopular political necessity.
I’m not even anti-nuclear myself, but let’s be clear: the worldwide nuclear energy industry is itself to blame for the lack of faith in nuclear energy.
Now, facing the growth of air travel, it was decided to raise this bar to 1 per billion hour. Not as an end by itself - this comes at very high cost and had a significant impact on travel prices. But because, with the growth of air travel, this would have implied one major accident per fortnight on average. And because those accident are more spectacular and relayed by media, civil aviation authorities feared this might raise angst and deter the public from air travel.
So, safety was enhanced, but mostly for marketing reasons.
which for 2019 describes "0.5 accidents per million departures" and "40 fatalities per trillion revenue passenger kilometers". Considering that many or most passengers fly close to 800-1000 km/h, we're still quite a bit above above 1 fatality per 100 million passenger hours.
Would a factor of 10 be enough? Suppose we go from one major accident per fortnight to one per five months (10 fortnights). Is that higher than what we have seen in the past thirty years?
Still your projection shows that both reference indicators and actual values are in the ballpark of the estimates I cited.
My (and Amalberti's) main point is that safety assessment is not just about minimizing the raw number of accidents, but involves tradeoffs between various concerns, including psychological perception and revenue. Otherwise, the safest airline would be the one that does not fly anyone.