Sequence of events
On 13 July 2004, at about 0710 Western Standard Time, the flight crew of an instrument flight rules Embraer-Empresa Brasilieira De Aeronautica EMB-120 ER (Brasilia), registered VH-ANJ, was on descent through 9,500 ft from Darwin to Kununurra Airport on airway J72 in visual meteorological conditions. The flight was a scheduled Regular Public Transport service. The pilot of a visual flight rules (VFR) Partenavia Costruzioni Aeronautiche SPA P.68B (Partenavia), registered VH-OAP, was tracking in the opposite direction from Kununurra to Darwin at 9,500 ft. The pilots were operating outside controlled airspace and beyond air traffic control radar coverage.
Approximately 50 NM before Kununurra at FL220, the Brasilia co-pilot broadcast the aircraft's position on the area frequency 122.4 MHz and advised that the aircraft was on descent to Kununurra. Just prior to the Brasilia leaving controlled airspace on descent, the Brisbane Centre controller advised the crew that there was no traffic for descent.
At approximately 0645, the Partenavia pilot broadcast the aircraft's position overhead Kununurra on the Mandatory Broadcast Zone (MBZ) frequency 127.0 MHz and reported tracking 023 degrees for Darwin at 9,500 ft. The pilot did not receive a response. He was operating outside the vertical and lateral confines of the MBZ at the time.
Approximately 30 NM before 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 stated that the Partenavia passed in close proximity and it was estimated that the distance between the aircraft was 40 m horizontally at the same altitude. The occurrence was classified as both an Airprox1, and a serious incident2.
Shortly after the aircraft passed, the Partenavia pilot heard the Brasilia crew broadcast their position and intentions on the MBZ frequency. They reported that they were 28 NM from Kununurra descending through 10,000 ft. The Partenavia pilot contacted the Brasilia crew and provided them with a position report and asked if they 'had him on TCAS' (traffic alert and collision avoidance system). The Brasilia crew replied that they were not TCAS equipped. The Partenavia pilot did not see the Brasilia.
The Brasilia crew stated that, when they were passing through 10,000 ft at 30 NM from Kununurra, they were in the process of changing over to the MBZ frequency to broadcast an inbound call.
The Partenavia pilot stated that his aircraft was equipped with two VHF communication systems, but the serviceability of one VHF communication system was 'questionable'. The Partenavia pilot stated that he would normally have the MBZ and area frequencies selected, but on this occasion, with only one serviceable VHF communications system, he elected to select the MBZ frequency.
The Partenavia pilot stated that he elected to monitor the MBZ frequency when transiting above Kununurra to identify potential conflicts with higher performing aircraft that might be inbound from Darwin to Kununurra, or outbound from Kununurra to Darwin. He was expecting that higher performing aircraft inbound to Kununurra would make a broadcast on the MBZ frequency before descending through 10,000 ft and at about 40 NM from Kununurra. In addition, the Partenavia pilot assumed that higher performing aircraft would be equipped with at least two VHF communication systems, one of which would be tuned to the relevant MBZ frequency well before the MBZ boundary. The pilot also commented that one of the reasons he remained on the MBZ frequency was that, under the National Airspace System, VFR pilots were discouraged from making radio calls on the area frequency.
The Partenavia pilot acknowledged that he was well outside the vertical and lateral confines of the MBZ when he had selected and remained on the Kununurra MBZ frequency. Had he selected the appropriate area frequency for the Kununurra region, he may have been alerted to the inbound Brasilia.
Some of the safety issues that pilots need to consider are the dangers of assuming that 'higher performance' aircraft are TCAS equipped and that crews can rely on it as a primary separation tool.
1 An Airprox is an occurrence in which two or more aircraft come into such close proximity that a threat to the safety of the aircraft exists or may exist, in airspace where the aircraft are not subject to an air traffic control separation standard or where separation is a pilot responsibility.
2 A serious incident is defined in Annex 13 to the Convention on International Civil Aviation, as:
An incident involving circumstances indicating that an accident nearly occurred.
Note 1 - The difference between an accident and a serious incident lies only in the result.
Attachment C to Annex 13 lists typical examples of incidents that are likely to be serious incidents and includes:
Near collisions requiring an avoidance manoeuvre to avoid a collision or an unsafe situation or when avoidance action would have been appropriate.
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