Aviation safety investigations & reports

Cessna Aircraft Company 172N , VH-IGA

Investigation number:
Status: Completed
Investigation completed


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.    
State: Queensland   Occurrence type: Separation issue  
Release date: 13 September 2000   Occurrence category: Incident  
Report status: Final   Highest injury level: None  

Aircraft 1 details

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 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  
Last update 13 May 2014