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A member of the public reported seeing a single engine aircraft manouevre suddenly to avoid another aircraft, on an intersecting track, while the aircraft were over Brisbane.

An investigation reviewed radar data and air traffic control automatic voice recordings to establish the sequence of events. The investigation found that VH-OXF, a Beech 300, was tracking for a left base to runway 01 at Brisbane Airport at 2,500 ft, while a Cessna 172, VH-IGA, was tracking north over the suburbs at 1,500 ft. The Brisbane departures controller established that the pilot of the Beech could see and was able to avoid the Cessna before reducing the vertical spacing between the aircraft to less than the vertical separation standard of 1,000 ft. The Beech pilot reported seeing and passing over the top of the Cessna and ready for further descent. The controller issued a clearance for a visual approach. The recorded radar data indicated that the Beech began a steady descent from about the intersection of the aircraft tracks.

The controller's options in relation to ensuring separation between the aircraft were either to:

  1. maintain the Beech at 2,500 ft until there was more than 3 NM lateral separation with the Cessna; or
  2. use visual separation procedures by having a pilot report seeing the other aircraft and then instructing that pilot to avoid the sighted aircraft.

To enable the Beech to descend in preparation for landing, the controller used the second option. Examination of the radar data indicated there was no infringement of separation standards.

The recorded radar data indicated that during the period when the Beech was assigned 2,500 ft, the Mode C altitude intermittently indicated 2,300 ft and 2,400 ft. Mode C altitude has a tolerance of plus or minus 200 ft. The pilot was therefore complying with the air traffic control clearance.

General details
Date: 06 July 2000 Investigation status: Completed 
Time: 1605 hours EST  
Location   (show map):11 km WSW Brisbane, Aero. Investigation type: Occurrence Investigation 
State: Queensland Occurrence type: Separation issue 
Release date: 13 September 2000 Occurrence class: Airspace 
Report status: Final Occurrence category: Incident 
 Highest injury level: None 
Aircraft 1 details
Aircraft manufacturer: Cessna Aircraft Company 
Aircraft model: 172 
Aircraft registration: VH-IGA 
Serial number: 17269546 
Type of operation: Aerial Work 
Damage to aircraft: Nil 
Departure point:Archerfield, QLD
Destination:Archerfield, QLD
Aircraft 2 details
Aircraft manufacturer: Beech Aircraft Corp 
Aircraft model: 300 
Aircraft registration: VH-OXF 
Serial number: FL122 
Type of operation: Unknown 
Damage to aircraft: Nil 
Departure point:Unknown
Destination:Brisbane, QLD
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Last update 13 May 2014