On 21 June 2012, after a
review of the initial Airservices Australia report of the
occurrence, the Australian Transport Safety Bureau (ATSB) initiated
an investigation into a breakdown of separation (BOS) between two
aircraft near Melbourne Airport, Victoria on 20 June 2012.
A preliminary examination of
the occurrence showed that the BOS involved an Airbus A320 aircraft
(A320) that was inbound to Melbourne Airport from the north and a
Bombardier Inc BD-700 aircraft (Bombardier) that had departed from
runway 34 at Melbourne and was tracking to the north-west. The ATSB
also reviewed information from the involved Melbourne Approach
Departures controller, the relevant air traffic control automatic
voice recordings, weather information from the Bureau of
Meteorology and the respective aircrafts flight tracks on Webtrack
recordings (see Airservices
WebTrak).
The preliminary investigation determined that the controller had
planned for a lesser rate of closure between the two aircraft than
eventuated, with the actual rate of closure being affected by the
ambient conditions and a slower acceleration by the Bombardier than
anticipated by the controller. No avoiding action was necessary by
either crew. The controller became aware of the infringement of the
3NM (5.6km) separation standard when advised by the crew of the
A320 that they had received a Traffic Alert and Collision Avoidance
System traffic advisory on passing behind the Bombardier. Shortly
after, the lateral and vertical distance between the two aircraft
increased and a separation standard was re-established.
The preliminary investigation showed that the potential for any
systemic issues to have contributed to the occurrence was low and
that it was unlikely that any safety issues would be identified
through further investigation. On that basis, the ATSB decided to
discontinue its investigation, as provided for in Section 21 (2) of
the Transport Safety Investigation Act 2003.