5.7 Monitoring of ACAS II Performance 5.7.1 ACAS II can have a significant effect on ATC. Therefore, there is a continuing need to monitor the performance of ACAS II in the developing ATM environment. 5.7.2 Following an RA event, or other significant ACAS II event, pilots and controllers should complete an ACAS II RA report. Aircraft Operators and ATS authorities should forward completed reports through established channels. 5.8 Overall Navigation (and Systems) Performance 5.8.1 All information relating to horizontal and vertical navigation (and systems) performance within the NAT Region is provided to the NAT SPG via the CMA. Regular statistical assessments of system safety determine whether or not the overall target level of safety (TLS) is being met. On those occasions that summary statistics show that the TLS, in either the horizontal or vertical planes, has been exceeded, the NAT SPG is informed in which case the NAT SPG will take appropriate action. It is the responsibility of the NAT SPG Scrutiny Group to make recommendations on an annual basis as to how safe operations can be maintained, unless there is a continued degradation in safety. The introduction of modern technology into aircraft systems has lead to a gradual reduction in the statistical risk of collision in the NAT, in spite of the continual increase in traffic.
