At 1310 Western Standard Time on 25 January 2012, a Bombardier Inc DHC-8-202 (Dash 8), registered VH-ZZI (ZZI), was on descent into Broome Airport. At about 17 NM, the flight crew of ZZI advised Broome Tower that they were descending in response to a Traffic Collision Avoidance System (TCAS) Resolution Advisory (RA) alert.

The first officer on ZZI sighted a Pilatus Aircraft Ltd PC-12/45 (PC12) about 1 NM ahead and reported that it passed about 200 to 300 ft to the right and slightly above them.

The traffic was identified as a PC-12, registered VH-MWO (MWO), that had departed Broome Airport at 1300. The pilot of MWO only became aware of the breakdown of separation after ZZI reported a TCAS Traffic Alert (TA), at which time he observed the Dash 8 on his TCAS, behind and on a reciprocal heading. The pilot did not recall hearing a TCAS audible alert.

Both aircraft were operating under Instrument Flight Rules (IFR) and were within airspace controlled by Broome Tower which utilised procedural separation.

The pilot of MWO had not selected automatic direction finding (ADF) as one of the active navigation aids in the aircraft's Electronic Flight Instrumentation System (EFIS). As a result, upon programming new information into the EFIS after departure, MWO unintentionally deviated from the desired outbound track and conflicted with the inbound track of ZZI.

Following the incident, the operator of MWO checked all aircraft in its fleet to ensure that the audio level of the TCAS could be heard above engine noise and radio traffic. MWO was the only aircraft that required the audio level to be increased.

This incident highlights the need for pilots to cross check aircraft navigation performance to ensure accurate track keeping particularly when operating in a procedural separation environment. The incident also highlighted the need to comply promptly with TCAS advisory alerts.