What happened
While operating at the non-controlled Mildura aerodrome, the flight crew of ZPJ, an unspecified aircraft type, and the pilot of XGA, an unspecified aircraft type, experienced a near-miss during circuit operations. The pilot of XGA was initially not monitoring the Mildura CTAF when the pilot monitoring on ZPJ broadcasted their intention to join the circuit. Upon switching to the frequency, the pilot of XGA was focused on communicating with another inbound aircraft and did not initially perceive ZPJ as a conflict.
As ZPJ transitioned to the base leg for runway 09, the crew issued a radio broadcast. Shortly after, the flight crew of ZPJ received a TCAS traffic advisory (TA) alert, which alerted them to the presence of XGA. Because ZPJ was flying below 900 feet, the TCAS resolution advisory was inhibited, but the visual display allowed the crew to identify XGA. The crew of ZPJ then instructed the pilot of XGA to turn south immediately to avoid a collision.
Despite the agreed separation strategy, XGA continued to converge toward ZPJ, reaching a closest point of approach of 0.12le NM behind and approximately 200 ft above ZPJ. This occurred as the pilot of XGA attempted to join the upwind leg of the circuit, unaware that ZPJ was also executing a go-around maneuver.
The investigation
Investigators examined the radio communications and cockpit environment leading up to the encounter. While both aircraft complied with required radio broadcasts, the investigation found that the pilot of XGA was likely not monitoring the correct frequency during the initial broadcast from ZPJ. Furthermore, the crew of ZPJ had previously dismissed other aircraft in the area as potential conflicts.
Findings
- The pilot of XGA was likely not monitoring the Mildura CTAF when the initial joining broadcast was made by ZPJ.
- The flight crew of ZPG failed to detect the broadcast from XGA regarding their intention to perform a straight-in approach.
- Radio interference from other aircraft operating at Mildura or Wentworth may have obscured critical communications.
- The pilot of XGA perceived ZPJ as stationary against the sky, while the crew of ZPJ saw XGA against a more complex background, complicating visual detection.
- The convergence of XGA to within 0.125 NM of ZPJ resulted from the pilot of XGA attempting to join the upwind leg before realizing ZPJ was performing a go-around.