Example of statistical techniques applied to autoland touchdown dispersion (confidence intervals for normal and skew distributions).
Abstract:ESDU 91019 illustrates certain aspects of statistical analysis introduced in ESDU 91017 applied to autoland touchdown dispersion. Two sets of data are analysed, one for the standard 3 degree glide slope and one for a STOL glide slope of 7.5 degrees with modified control laws. Each set consisted of 1480 points giving frequency of touchdown in various 100 ft intervals from the threshold. The data are analysed to establish the mean touchdown distance, the probability of touching down either short or long (200 ft before or 3000 ft beyond the threshold) and the touchdown distance three standard deviations beyond the touchdown point. The Chi Squared Test applied to the first set of data shows a high confidence that they are Normal, and so the required results are obtained by plotting the percentage cumulative frequency data against touchdown distance using Normal/probability graph paper. When the Chi Squared Test is applied to the second data set, the confidence in their normality is found to be only 19 per cent. A transformation of the data is therefore tried, taking the logarithm of the touchdown distance which greatly increases the confidence in normality established by the Chi Squared Test. The log data are then analysed using the Normal/probability graph paper as for the first data set.
|Data Item ESDU 91019|