Loss of separation involving a Bombardier DHC-8-402 and a Boeing 737-838, 92 km south-west of Balranald Airport, Victoria, on 4 March 2018

What happened

On 4 March 2018, a Bombardier DHC-8 (DHC-8) departed Mildura Airport, Victoria (Vic.), for Melbourne Airport, Vic. During climb, the flight crew requested clearance to climb to FL 250^[1] and were approved by ATC to climb to FL 240.

A Boeing 737 (737) was en route from Adelaide Airport, South Australia (SA), to Sydney Airport, New South Wales (NSW), maintaining FL 250 on a crossing track.

At 1744 Eastern Standard Time (EST), ATC cleared the DHC-8 to climb from FL 240 to FL 250 resulting in a loss of separation with the 737. ATC subsequently received a short-term conflict alert (STCA). ATC instructed the crew of the DHC-8 to maintain FL 240 but as the DHC-8 was already climbing through FL 245, ATC instructed the crew to descend and turn left onto heading 090. They then instructed the crew of the 737 to turn right immediately onto heading 180 for separation. Once the separation standard was regained, the DHC-8 was cleared to climb to FL 250 and both aircraft continued without incident.

Separation reduced to 900 ft between the aircraft when they were 5 NM apart. Neither flight crew received a TCAS resolution alert (RA).

Safety message

This incident shows the effectiveness of the ATC short term conflict alert (STCA) system and conflict resolution training received by ATC for loss of separation events. It also highlights the importance of flight crews responding immediately to ATC instructions.

About this report

Decisions regarding whether to conduct an investigation, and the scope of an investigation, are based on many factors, including the level of safety benefit likely to be obtained from an investigation. For this occurrence, no investigation has been conducted and the ATSB did not verify the accuracy of the information. A brief description has been written using information supplied in the notification and any follow-up information in order to produce a short summary report, and allow for greater industry awareness of potential safety issues and possible safety actions.

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1. Flight level: at altitudes above 10,000 ft in Australia, an aircraft’s height above mean sea level is referred to as a flight level (FL). FL 250 equates to 25,000 ft.