This report examines what, if any, trends may be emerging as a
result of the introduction of NAS stage 2b from 27 November 2003.
Four indicators - airprox, breakdown of separation (BOS),
resolution advisories (RA) and violation of controlled airspace
(VCA) - were analysed to assess any net effects resulting from NAS
2b changes. There was no significant change in the rate of
airproxes per aircraft movement in the 180-day period after NAS 2b
was introduced relative to the 180-day period immediately before.
There was also no significant change in airproxes involving RPT
aircraft. There was a reduction in the rate of BOS incidents per
aircraft movement in the post-NAS 2b period compared with the
period immediately before, but this was not statistically
significant. Analysis of RA incidents indicated no statistically
significant change in the rate per movement reported after NAS 2b
was introduced compared with the period immediately before.
Overall, the report concludes that data currently available do not
enable reliable conclusions to be drawn about NAS 2b safety
trends.