On 16 February 2012, a Government Aircraft Factory N22C, registered VH‑ATO (ATO), was conducting a survey flight north-east of Melbourne Airport, Victoria when it was involved in two losses of separation with two Boeing 737 aircraft. The 737s, registered VH‑VZA (VZA) and VH‑TJY (TJY), were on approach to runway 27 at Melbourne Airport. All of the aircraft were in receipt of an air traffic control service.
What the ATSB found
Although air traffic control intended that the pilot of ATO should keep his aircraft separate from VZA and TJY using visual observation (visual (pilot) separation), not all the prerequisites for using this separation method were met. As a result, the onus remained on air traffic control to maintain either a vertical separation standard of 1,000 ft or a surveillance separation standard of 3 NM (5.6 km). Losses of separation occurred when separation between ATO and VZA reduced to 1.5 NM (2.8 km) and 300 ft, and between ATO and TJY when separation reduced to 1.7 NM (3.2 km) and 700 ft.
The ATSB also identified that the controller was not aware of how specific aspects of the survey operation were to be conducted and therefore could not be assured that separation would be maintained.
Additionally, the ATSB identified that limited guidance and training was provided to controllers operating outside the towered environment in the application of the visual (pilot) separation standard, increasing the risk of the incorrect application of the standard.
What's been done as a result
In response to these occurrences, Airservices Australia amended the Manual of Air Traffic Services to include a number of factors to be considered by air traffic controllers prior to assigning visual (pilot) separation. In addition, the training package for Melbourne Airport arrivals controllers was reviewed and updated to ensure that visual separation, transfer of separation responsibilities and associated phraseologies were adequately addressed. Finally, the controller checking regime was strengthened to ensure that any identified training and/or knowledge deficiencies in relation to assigning visual separation, and their impact on controller performance, were addressed.
The use of visual (pilot) separation transfers responsibility for separation between aircraft operating in controlled airspace from the air traffic controller to the flight crew of one of the aircraft. This occurrence highlights that, for the standard to be effective, all parties must have a shared understanding. Correct application of the visual (pilot) separation standard ensures that all involved flight crew are aware of their responsibility, thereby assuring that aircraft will not come into unsafe proximity.