[SystemSafety] A different Historical Question

[SPRIGGS, John J]

Way back in the last millennium, someone did an analysis of aircraft accident data, selected out a set based on various criteria, such as 'western built' commercial air traffic in controlled airspace, etc., and came up with a figure for accidents per flight.
On behalf of ECAC, someone applied an improvement factor, truncated the answer to two decimal places and declared a 'safety target' of better than 2.31x10^-8 accidents per flight.  At that time, it was conventional to assume an average flight is ninety minutes. This was applied to the result and rounded up to give a target of better than 1.55x10^-8 accidents per controlled flying hour.
I used to have references for these things, but I have lost them (the ECAC targets are quoted in a document called ESARR4 which is still available despite being obsolete in the EU for over a decade). In particular I wanted a reference for the ninety minute flight convention.  This is because I have been shown a standard (not from the commercial air traffic domain) that takes the ECAC targets as the basis for arguing that the average length of a flight is 89.4 minutes, i.e. taking the truncated and rounded results as 'truth' ...  I would like to challenge it with references.


John





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