Breakdown in separation involving Boeing 747-400, VH-OJG and Piper PA31-350, VH-WGG, near Mona Vale, New South Wales, on 24 November 1992

VH-WGG departed Williamtown at 0703 hours and proceeded to track via the 015 radial of the Sydney VOR at 8,000 ft. The pilot contacted the Sydney Departures North controller 28 NM from Sydney and the radar identification was passed to the Approach North controller, who raised a 'shrimp boat' (a small piece of plastic which adheres to the radar screen and allows the controller to write pertinent information on it for his/her reference) and placed it on the radar screen next to the radar return of VH-WGG.

The shrimp boat was not positionally updated nor was it annotated to indicate to which aircraft it was referring. When an aircraft passes overhead Sydney, its track impinges on all four sectors of approach/departures airspace and two flight progress strips (FPSs) are raised, one for approach use and one for departures. These FPSs are pink in colour to enable them to stand out from the other FPSs in use.

The aircraft is identified by the controller in whose airspace it enters, and the progress is then monitored by all four controllers by updating the position of their 'shrimp boats' on the radar screen and placing the pink FPS in the central (active) strip bay.