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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