Final Report


What happened

On 3 September 2015, several multi-engine turboprop aircraft converged on the airspace above Mount Hotham Airport, Victoria, as part of a multi-day charter involving several operators. While conducting a number of area navigation (RNAV) Global Navigation Satellite System (GNSS) approaches, the pilot of a participating Beech Aircraft Corp B200 (King Air) aircraft, registered VH‑OWN, descended the aircraft below the minimum altitude and exceeded the tracking tolerance of the approach after experiencing GPS/autopilot difficulties. The pilot twice climbed the aircraft without following the prescribed missed approach procedure and manoeuvred in the Mount Hotham area. During this manoeuvring, the aircraft came into close proximity to another King Air, registered VH‑LQR, which had commenced the same approach. Both aircraft were in instrument meteorological conditions and unable to sight each other. Significant manoeuvring was also observed as VH‑OWN was on final approach to the Mount Hotham runway. All aircraft landed safely at Mount Hotham without injury to passengers or crew.

What the ATSB found

Difficulties in operating the GPS/autopilot resulted in the pilot of VH‑OWN experiencing an unexpected reduction in the level of supporting flight automation, and a significant increase in workload, while attempting to conduct RNAV (GNSS) approaches into Mount Hotham Airport. This increased workload affected both the pilot’s ability to follow established tracks such as the published approach and missed approach, and his ability to communicate his position accurately to other aircraft and the air traffic controller.

Although radar coverage in the area was limited, there were opportunities for the air traffic controller to identify when VH‑OWN was having tracking difficulties during all three approaches, and when VH‑OWN tracked towards the expected position of VH‑LQR. However, this position information was not effectively communicated, resulting in a missed opportunity to prevent a potential controlled flight into terrain and/or collision with VH‑LQR.

What's been done as a result

The pilot of VH‑OWN underwent flight testing by both a delegate of the Civil Aviation Safety Authority (CASA), and by a flying operations inspector employed by CASA, who recommended remedial training. Independent of this investigation, in February 2017 it became mandatory for all aircraft operating under instrument flight rules to be fitted with Automatic Dependence Surveillance – Broadcast, further increasing surveillance capability nationally, including in the Mount Hotham area.

Additionally, and independent of this investigation, the Department of Defence radar system, capable of surveillance in the Mount Hotham area, is scheduled for upgrade in late 2018. The radar system upgrade is likely to enhance the national air traffic system through the increased compatibility between that radar and the Airservices Australia surveillance system.

Safety message

Maintaining the pilot skill of operating an aircraft without the use of automation is essential in providing redundancy should the available automation be unexpectedly reduced. Additionally, as the responsibility for separation from other airspace users and terrain in Class G airspace lies with aircrew, it is imperative that pilots maintain the skills to navigate accurately, and interpret and utilise traffic information to maintain safe separation. From an air traffic control perspective, the occurrence highlights the safety benefit of communicating any apparent tracking anomalies and/or conflicts to the involved pilots.

Mount Hotham runway
Mount Hotham runway Source: Mount Hotham Airport and ResortSource: Mount Hotham Airport and Resort

The occurrence


Safety analysis


Sources and submissions