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A Boeing 747-200 (B747) was being radar vectored from the west for sequencing to runway 21 at Perth. A de Havilland Canada DHC-8-102 (Dash 8) was being radar vectored from the east for sequencing to land on runway 21 behind the B747. When the crew of the Dash 8 reported that they had sighted the B747, the air traffic controller assigned them the responsibility for separation from the B747. The rate of closure between the two aircraft was high and the crew of the Dash 8 received a traffic advisory from their traffic alerting and collision avoidance system. Although the Dash 8 crew was being issued with radar vectoring instructions by air traffic control, they were obliged to turn their aircraft to the right to avoid the B747.

Radar data and air traffic control automatic voice recordings were reviewed to establish the sequence of events. The investigation found that the approach controller had assigned the responsibility for separation to the pilot of the arriving Dash 8 while the aircraft was being radar controlled. The radar separation standard required 3NM horizontal separation while there was less than 1,000ft of vertical separation. During the occurrence, radar separation reduced to 1.82NM when there was 100ft vertical separation. A radar or vertical separation standard was not required when some other form of separation was being applied. In this situation the controller was relying on visual separation.

Visual separation of air traffic may have been a valid method to use in circumstances where less than the required radar separation is achievable. However, the criteria for the application of the standard were clearly detailed in the Manual of Air Traffic Services (MATS) Part 4 Section 5. In particular, MATS stated:`In circumstances where an aircraft has been instructed to maintain separation from, but not follow, an IFR aircraft, traffic information shall be issued to the IFR aircraft, including advice that responsibility for separation has been assigned to the other aircraft'. The arriving B747 was an IFR aircraft but was not provided with the required traffic information.


Local safety action

As a result of this investigation, Airservices Australia provided the Australian Transport Safety Bureau with the following response. `The information you provided with respect to the application of visual separation as per MATS was discussed with some and forwarded to all Business Unit procedures specialists for appropriate action. Additionally, it was forwarded to local QA areas and DSEA audit for follow up ensuring the ongoing correct application of this procedure'.

General details
Date: 25 June 2001 Investigation status: Completed 
Time: 1100 hours WST  
Location   (show map):15 km NNE Perth, (VOR) Investigation type: Occurrence Investigation 
State: Western Australia Occurrence type: ACAS warning 
Release date: 18 July 2002 Occurrence class: Airspace 
Report status: Final Occurrence category: Incident 
 Highest injury level: None 
Aircraft 1 details
Aircraft manufacturer: de Havilland Canada 
Aircraft model: DHC-8 
Aircraft registration: VH-XFT 
Serial number: 052 
Type of operation: Air Transport Low Capacity 
Damage to aircraft: Nil 
Departure point:Plutonic Mine, WA
Departure time:0905 hours WST
Destination:Perth, WA
Aircraft 2 details
Aircraft manufacturer: The Boeing Company 
Aircraft model: 747 
Aircraft registration: ZS-SAL 
Type of operation: Air Transport High Capacity 
Damage to aircraft: Nil 
Departure point:Johannesberg, SOUTH AFRICA
Destination:Perth, WA
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Last update 13 May 2014