Incident Overview
On 6 June 2023, a Piper PA-28-161, registered VH-ENL, taxied for runway 36 at Mildura Airport, Victoria, for a private flight to Broken Hill, New South Wales. At approximately the same time, a QantasLink Bombardier DHC-8-315, registered VH-TQH, began taxiing for runway 09 on a scheduled passenger service to Sydney. Both aircraft made taxi, entry, and backtrack calls on the local common traffic advisory frequency (CTAF). The PA-28 pilot was aware of the Dash 8 backtracking on runway 09, but the Dash 8 crew was not aware that the PA-28 was preparing for takeoff from the cross runway. The Dash 8 commenced its takeoff as the PA-28 initiated its rolling call on runway 36. The Dash 8 crossed the runway 09/36 intersection ahead of the PA-28 by about 600 m laterally and 200 ft vertically.
ATSB Findings
The Australian Transport Safety Bureau (ATSB) investigation identified that the PA-28 pilot incorrectly identified the runway direction during taxi and radio calls, saying "runway 35" instead of "runway 36" on two occasions. The Dash 8 crew, focused on obtaining their pre-departure transponder code from air traffic control, had the CTAF radio volume turned down. An over-transmission from air traffic control also masked parts of the PA-28's calls. These factors likely led to the Dash 8 crew's incomplete comprehension of traffic; they believed the PA-28 was not at Mildura. However, they did not seek further information to positively identify the traffic. The PA-28 pilot assumed the Dash 8 was still backtracking on runway 09, was unable to visually sight the Dash 8 due to airport buildings, and did not directly contact the Dash 8 to coordinate separation. The ATSB also found that the Dash 8 crew did not make a rolling call on runway 09, which was not a requirement at the time, based on their mental model of local traffic. Airport topography and buildings prevent direct visibility between aircraft on the thresholds of runways 09, 27, and 36.
Safety Actions
Following the incident, QantasLink updated its operations manual to require rolling calls at all CTAF aerodromes, improving procedural consistency. The airline also provided guidance to pilots on potential radio wave degradation at Mildura between runway 36 and 09 thresholds, including the conduct of rolling calls and clarification of ambiguous radio calls from other aircraft prior to departure. The ATSB is further investigating potential radio interference at Mildura Airport in a related investigation (AO-2023-050) involving a similar event approximately three months later. The ATSB continues to work with Qantas Safety, Mildura Airport, the Australian Communications and Media Authority, CASA, and Airservices Australia to identify potential radio communication interference and shielding issues.