Aviation safety investigations & reports

Airbus Industrie A320-211 , VH-HYF

Investigation number:
Status: Completed
Investigation completed


The crew of an Airbus A320, operating under instrument flight rules (IFR), was cleared to descend to 4,000 ft on a BROOK TWO standard arrival route. The approach radar controller advised the A320 crew of two other aircraft, operating outside controlled airspace, on the reciprocal track to their aircraft. The controller reported a primary radar return only on the first aircraft and that the second aircraft was indicating an unverified Mode C altitude of 3,500 ft. The lower limit of controlled airspace in the area was 3,500 ft and was available for use by aircraft outside controlled airspace.

The pilot of the A320 levelled the aircraft at 4,300 ft and maintained that altitude until both pilots sighted the first aircraft. The A320 crew then received a Traffic Alert and Collision Avoidance System (TCAS) traffic advisory alert on the second aircraft. The TCAS indicated that the second aircraft was 800 ft below the A320. The crew then sighted that aircraft.

The minimum vertical separation requirement between an IFR aircraft in controlled airspace, and an aircraft operating under visual flight rules outside controlled airspace is 500ft. This spacing may on occasions be insufficient to prevent activation of a TCAS alert, or to provide adequate wake turbulence separation between aircraft.

Safety Action

As a result of this occurrence, the Bureau of Air Safety Investigation is currently investigating a perceived safety deficiency. The deficiency relates to wake turbulence separation standards between aircraft operating within controlled airspace and those operating at or below the lower limit of controlled airspace.

Any safety output issued as a result of this analysis will be published in the Bureau's Quarterly Safety Deficiency Report.

General details
Date: 06 October 1998   Investigation status: Completed  
Time: 1400 hours WST    
Location   (show map): 28 km SE Perth, Aero.    
State: Western Australia   Occurrence type: ACAS warning  
Release date: 04 August 1999   Occurrence category: Accident  
Report status: Final   Highest injury level: None  

Aircraft 1 details

Aircraft 1 details
Aircraft manufacturer Airbus Industrie  
Aircraft model A320  
Aircraft registration VH-HYF  
Serial number 027  
Type of operation Air Transport High Capacity  
Damage to aircraft Nil  
Departure point Melbourne, VIC  
Destination Perth, WA  

Aircraft 2 details

Aircraft 2 details
Aircraft manufacturer Unknown  
Aircraft model Aeroplane  
Damage to aircraft Nil  
Departure point Unknown  
Destination Unknown  
Last update 13 May 2014