An ATSB report has found that a recent airspace incident was both an 'airprox' and a 'serious incident' and that a Brasilia and a Partenavia aircraft passed about 40 m horizontally at the same altitude from each other.
The flight crew of the instrument flight rules (IFR) Brasilia was on descent through 9,500 ft from Darwin to Kununurra Airport on airway J72 in visual meteorological conditions (VMC). The flight was a scheduled Regular Public Transport (RPT) service. The pilot of a visual flight rules (VFR) Partenavia was tracking in the opposite direction from overhead Kununurra to Darwin at 9,500 ft. The pilots were operating outside controlled airspace and beyond air traffic control radar coverage.
Approximately 50 NM north-north-east of Kununurra at FL220, the Brasilia co-pilot broadcast the aircraft's position on the area frequency 122.4 MHz and that the aircraft was on descent to Kununurra.
The Partenavia pilot broadcast the aircraft's position overhead Kununurra on the mandatory broadcast zone (MBZ) frequency 127.0 MHz and reported tracking 023 for Darwin at 9,500 ft. He was operating outside the vertical and lateral confines of the MBZ and did not receive a response.
Approximately 30 NM north of Kununurra, as the Brasilia was descending through 9,500 ft, the pilot in command briefly saw a Partenavia, in his peripheral vision, fly past the Brasilia's left wing. Visibility at the time was reported as very good. The Brasilia crew estimated that the distance between the aircraft was 40 m, at the same altitude. There was insufficient time to take evasive action. The Partenavia pilot did not see the Brasilia.
The ATSB investigation found that had the Partenavia pilot selected the appropriate area frequency for the Kununurra region, he may have been alerted to the inbound Brasilia. In addition, some of the safety issues that pilots need to consider are the dangers of assuming that higher performance aircraft are TCAS (traffic alert and collision avoidance system) equipped and that crews can rely on it as a primary separation tool.
The airspace in which the incident occurred was not restructured as part of the National Airspace System (NAS).
The full investigation report (200402626) is available from the Bureau's website, or from the Bureau on request.