United States Department of Transportation
i
Predicting General Aviation Accident Frequency from Pilot Total Flight Hours
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2012-10-01
[PDF-1.57 MB]
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Abstract:Craig (2001) hypothesized a “killing zone”—a range of pilot total flight hours (TFH) from about 50-350, over
which general aviation (GA) pilots are at greatest risk. The current work tested a number of candidate modeling
functions on eight samples of National Transportation Safety Board GA accident data encompassing the years
1983-2011. The goal was largely atheoretical, being merely to show that such data can be modeled.
While log-normal and Weibull probability density functions (pdf) appeared capable of fitting these data, there
was some pragmatic advantage to using a gamma pdf. A gamma pdf allows estimation of confidence intervals
around the fitting function itself. Log-transformation of TFH proved critical to the success of these data-fits.
Untransformed TFH frequently led to catastrophic fit-failure.
Due to the nature of the data, it may be advisable to place the greatest prediction confidence in a middle range of
TFH, perhaps from 50-5,000. Fortunately, that is also the range that captures the vast majority of all GA pilots.
With some care, GA accident frequencies appear predictable from TFH, given data parsed by a) pilot instrument
rating and b) seriousness of accident. Goodness-of-fit (R2) tended to be excellent for non-instrument-rated pilot
data and good for instrument-rated data. Estimates of median TFH were derived for each dataset, which will be
useful to aviation policy makers.
These data suggest that the “killing zone” proposed by Craig may be wider than originally believed.
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