Hello All,
I'm reading "Flight Performance" ATPL book and the following is stated there:
NET PERFORMANCE
Net performance is the gross performance diminished to allow for various contingencies that cannot be accounted for operationally e.g., variations in piloting technique, temporary below average performance, etc. It is improbable that the net performance will not be achieved in operation, provided the aeroplane is flown in accordance with the recommended techniques. This level of performance is approximately 5 standard deviations from the average performance or gross performance. Therefore, 99.99994% of the time, the aeroplane will achieve net performance or better. However, there is less than one chance in a million that the aeroplane will not achieve the net performance. This is the safety standard which the aviation authorities aim to achieve.
It is absolutely clear, but does anyone know where does "5 standard deviations/99.99994%" come from? I mean ICAO docs, or some EASA or national documents? I've made some search, but was unable to figure out.
Thanks a lot.