[SystemSafety] Difference between software reliability and astrology

[Derek M Jones]

Steve,

Thanks for the numbers update.

> 5 hours per day is way too low. Airplanes are very expensive, airlines are low profit margin businesses (which is why they are so interested in other, more highly profitable side business like credit cards), and airplanes only earn revenue when they are in the air.

I was not sure whether there was a long tail of less
frequently used aircraft.

> So if you double or triple your numbers below to account for 10-15 flight hours per day instead of the 5 you used, you get:
> 
> — 1 X 10^-5 equates to 2.5 to 3.75 Abnormal procedures per day
> 
> — 1 X 10^-7 equates to one Emergency procedure or Airplane damage every 30 to 45 days
> 
> — 1 X 10^-9 equates to one Catastrophic Accident every 6 to 10 years

To me 6-10 years is not Extremely improbable.
Perhaps the reliability figures were chosen when there were an order
of magnitude fewer aircraft.

Multiplying these values by lots of orders of magnitude implies
that self-driving car incidents are going to be routine.

-- 
Derek M. Jones           Evidence-based software engineering
blog:https://shape-of-code.com