On 28 September 2012, an en route air traffic controller acknowledged a Route Adherence Monitor (RAM) alert in respect of a Boeing Company 737‑8BK aircraft, registered VH-VUM (VUM), on a scheduled passenger service between Sydney, New South Wales and Brisbane, Queensland. Believing that VUM was destined for Newcastle Airport under Department of Defence air traffic control jurisdiction, the controller erroneously inhibited the flight data record (FDR) for VUM. This action cancelled the RAM alert.
The inhibition of the FDR, in combination with the controller’s altitude filter being set at a lower flight level than appropriate to the combined sectors under the controller’s jurisdiction, meant that VUM’s FDR registered as a ‘not concerned’ aircraft track. Subsequently, due to this ‘not concerned’ status, the controller did not see or interrogate VUM’s FDR for the rest of the time it was under their jurisdiction. Similarly, the FDR did not attract the attention of two Inverell sector controllers after it entered and crossed their sector until they responded to a frequency change request from the flight crew of VUM.
There was no loss of separation with other aircraft for the resulting period that the aircraft operated without the active provision of ATC services and, during the course of the occurrence, two-way communications in controlled airspace remained available. However, maintenance of the minimum aircraft separation standards during this period was not assured. There was a loss of separation assurance.
What the ATSB found
High-reliability systems like air traffic control have many layers of controls to minimise risks associated with operational hazards. These controls were ineffective in this case as a result of a number of factors, including human perception and attention issues, the training of controllers with regard to ‘not concerned’ tracks, and the level of system protection against the potential impact of such tracks. Specifically, error‑tolerant system designs that aid in the detection and recovery of inadvertently-inhibited tracks offer another defence against this type of occurrence.
Two safety issues were identified as a result of this investigation. The first relates to the provision of awareness training for en route controllers who are routinely exposed to ‘not concerned’ radar tracks, which can lead to a high level of expectancy that such tracks are not relevant for aircraft separation purposes. The second issue relates to the limited protections against a controller mistakenly inhibiting an aircraft and need for procedures to account for the limitations in the interoperability between the Australian Advanced Air Traffic System/Australian Defence Air Traffic System.
What's been done as a result
In response to the occurrence, Airservices has amended its air traffic controller ab-initio training exercises to include ‘not concerned’ track scenarios to ensure that training emphasised the importance of scanning ‘not concerned’ radar tracks. The scenarios will also be included in operational simulation training where appropriate. Furthermore, Airservices will use this occurrence to raise awareness of black tracks and the need to scan ‘not concerned’ tracks amongst its air traffic control staff.
In respect of equipment interoperability, Airservices and the Department of Defence are currently working towards implementing a harmonised joint civil military air traffic service system via the OneSky Program. Once implemented this system will increase air traffic management interoperability between both organisations.
This occurrence highlights the fallibility of human attention/perception and the resulting risk of involved parties being ‘primed’ to the circumstances of an occurrence to the extent that they automatically (but incorrectly) perform actions that they perceived were correct. There is the potential for additional error-tolerant design improvements to complement existing air traffic system human machine interface risk controls to reduce the likelihood of such behaviour.
Humans can also experience difficulty detecting display targets that are subtle, unexpected and deemed of low information value. This occurrence showed a reduced awareness among controllers of the potential impact of black, ‘not concerned’ tracks in an en route airspace environment, which might be addressed by additional controller training or through an integrated air traffic management system.