Owen Stanley in his Post number 243 claimed that the diagram in the Ambidji Report which has been discussed was only a “labelling error”. He believes that the correct calculations were performed by Ambidji.
I have recently had advice from a friend who has expertise in mathematics. He does not agree with Owen Stanley. This is what he says:
The graph on the next page, Fig 11.5 page 141, compares actual collision frequencies and those calculated by Ambidji from the US empirical data.
If you compare the data in this graph you get the following comparison between the values calculated by Ambidji and the correct calculation using the US FAA empirical data.
The figure on page 141 (fig 11.5) shows the following comparison:
....................................................Rate From
....................................................the Graph
........................................US.......Fig. 11.5 p.141
Location........Movements.....Calc'n....(Ambidji calc)
Archerfield.......146,000.......0.018.......0.02
Bankstown.......418,000.......0.146.......0.08
Jandakot.........414,000.......0.143.......0.09
Moorabbin.......372,000........0.115.......0.06
Parafield.........141,000........0.017.......0.025
The result for Archerfield is curious. The rest are consistent with the mistaken calculation.
The calculation should be accidents pa = 0.834 x M x M Where M = number of millions of movements
ie for 418,000 movements M = 0.418 0.834 x 0.418 x 0.418 = 0.146
It was my first assumption that the graph was simply mislabeled but Fig 11.5 is where Ambidji compare the GAAP outcomes with the US data for Class D towers shows the result was incorrectly calculated..
The final calculations by Ambidji did use the historic data as follows.
Ambidji took the most recent 9 years which included a cluster of accidents - 7 in all at 6 aerodromes. And based on this scant data calculated a separate accident frequency at 6 airports !!
They did this as follows.
Data this scarce must have a large amount of scatter. They accepted as 'correct' the high results and they filled in the low results with additional hypothetical accidents calculated from the US empirical data.
This is so scientifically invalid that one is left speechless.