The report presented was prepared principally from the
information supplied to the Bureau.
Reported Information
On 21 October 2004, at about 1150 Central Standard Time, a
Boeing Company 737-76N aircraft (737) registered VH-VBN was
tracking to Alice Springs Airport on the 122 radial of the VHF
omnidirectional radio range (VOR) navigation aid on descent to
9,000 ft. The crew reported that at about 35 NM from the airport,
they received a traffic alert and collision avoidance system (TCAS)
traffic advisory (TA) alert. Shortly after, the crew received a
TCAS resolution advisory (RA) to reduce the aircraft's rate of
descent. After changing to the Alice Springs aerodrome controller's
(ADC) frequency, the crew was provided with traffic information on
a Beech Aircraft Corporation 58 Baron aircraft (Baron), that was in
the vicinity of the 737 at 9,500 ft and tracking in the opposite
direction.
The ADC provided an air traffic service in the Class D control
zone and the Class E control area steps surrounding the Alice
Springs Airport, from ground level to 8,500 ft, within an area
encompassed by a circle with a radius of 36 NM centred on Alice
Springs Airport. Controllers were required, in Class D airspace, to
separate instrument flight rules (IFR) flights from other IFR
flights and to provide traffic information to pilots of IFR flights
about any visual flight rules (VFR) flights. A similar level of
service was required within Class E airspace for IFR flights with
the exception that pilots of IFR flights would be provided with
traffic information on VFR flights as far as practicable. The 737
was an IFR category flight and the Baron was a VFR category
flight.
The ADC had flight details on both aircraft and it would have
been prudent to provide traffic information to the crew of the 737
in sufficient time to enable them to assess the likelihood of a
conflict in either class of airspace. At the time of the occurrence
the ADC was busy with coordination tasks and managing other
aircraft.
On 25 November 2004, as a result of National Airspace System
(NAS) changes, the Class E airspace around Alice Springs was
changed to Class C. In Class C airspace controllers are required to
separate IFR flights from other IFR and VFR flights. Consequently,
in future similar circumstances the ADC will be required to
separate the aircraft.