Aeronautical Study of Port Macquarie - Civil Aviation Safety Authority

Office of Airspace Regulation Page 42 of 69
8.3 Results
The ARM considered the following protection barriers:
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Ground control: - Not provided, no claim made e.g. failure rate =1
1st aircraft considered action based on CTAF frequency and protocols (e.g.
H-V pair 3.23% failure)
2nd aircraft considered action based on CTAF frequency and protocols (e.g.
H-V pair 16.4% failure)
Common mode failure (no working radio or wrong frequency) ( e.g. H-V pair
1.11% failure)
Combination of mutual considered action or common mode leads to
avoidance action failure (e.g. H-V pair 1.63% failure)
1st aircraft evasive action VMC based on unalerted see and avoid protocols
(e.g. H-V pair 31.2% failure)
2nd aircraft evasive action VMC based on unalerted see and avoid protocols
(e.g. H-V pair 25.5% failure)
Combination of mutual evasive action in VMC (e.g. H-V pair 7.95% failure)
Note evasive action fails in IMC. No claim made
Conflict geometry – collision avoided due to chance (e.g. H-V pair 0.2%)
The model assumes that a mid-air collision will occur if a conflict pair exists and all
six barriers fail. (e.g. H-V pair VMC 2.6 chances in a million).
Table 3 presents the results for all ten pairs for VMC and IMC (expressed in terms of
chances per million). MAC probabilities are then given, also on chances per million,
as the composite of likelihood per pair times the number of pairs derived from the
movement data for PMQ.
1 st aircraft V L L M M M H H H H
2 nd aircraft V V L V L M V L M H
VMC generic 2.24 1.07 0.17 1.96 0.13 0.04 2.6 0.15 0.04 0.13
IMC generic 2.48 1.84 0.84 3.177 1.31 2.18
PMQ MAC probability 718 141 43 54 6 0.6 93 12 1 3
Table 3 – Mid air collision probability as generic likelihood multiplied by no. of conflict pairs for
PMQ
Airspace Review of Port Macquarie (YPMQ) May 2010 Version 1.0