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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.

General details
Date: 21 October 2004 Investigation status: Completed 
Time: 1150 CST  
Location   (show map):65 km SE Alice Springs, Aero. Investigation type: Occurrence Investigation 
State: Northern Territory Occurrence type: ACAS warning 
Release date: 31 October 2005 Occurrence class: Airspace 
Report status: Final Occurrence category: Incident 
 Highest injury level: None 
Aircraft 1 details
Aircraft manufacturer: The Boeing Company 
Aircraft model: 737 
Aircraft registration: VH-VBN 
Type of operation: Air Transport High Capacity 
Damage to aircraft: Nil 
Departure point:Sydney NSW
Departure time:0927 CST
Destination:Alice Springs NT
Crew details
RoleClass of licenceHours on typeHours total
Aircraft 2 details
Aircraft manufacturer: Beech Aircraft Corp 
Aircraft model: 58 
Aircraft registration: VH-XSY 
Type of operation: Private 
Damage to aircraft: Nil 
Departure point:Alice Springs NT
Departure time:1143 CST
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Last update 13 May 2014