Aviation safety investigations & reports

Airborne collision alert involving AgustaWestland AW139, VH-YXH and Piper PA-44-180, VH-HMQ Mangalore Airport, Victoria on 6 June 2021

Investigation number:
Status: Completed
Investigation completed
Phase: Final report: Dissemination Read more information on this investigation phase


Download Final report
[Download  PDF: 1.09MB]

What happened

On the afternoon of 6 June 2021, a Babcock Mission Critical Services Australasia, AgustaWestland AW139 helicopter, registered VH-YXH, was conducting a medical retrieval flight from Yielima, Victoria to the Royal Melbourne Hospital. The helicopter was being operated under the instrument flight rules (IFR). At the same time, a Moorabbin Aviation Services Piper PA-44-180 Seminole aircraft, registered VH-HMQ, was operating an IFR training flight from Wagga Wagga, New South Wales to Mangalore Airport, Victoria.

As the Seminole tracked north along the RNAV-Z runway 36 approach to Mangalore Airport, the helicopter was about 10 NM north of Mangalore and tracking south to overfly the airport at 3,100 ft. At about 1555, the Seminole commenced a missed approach resulting in the helicopter’s traffic alerting and collision avoidance system (TCAS) displaying a traffic advisory, followed by a resolution advisory. Six seconds later, the aircraft passed in cloud 451 m (in a straight line) from each other with a minimum vertical separation of 543 ft and a minimum horizontal separation of 333 m. Both aircraft were in cloud throughout the occurrence.

The helicopter continued to Royal Melbourne Hospital while the Seminole diverted to Shepparton. Both aircraft landed without further incident.

What the ATSB found

The helicopter pilot did not consider the possibility of the pilot in the Seminole conducting a missed approach and that it could conflict with the helicopter’s flight path. The Seminole’s pilot reported not hearing broadcasts from the helicopter and misinterpreted traffic advice from air traffic control. Consequently, the Seminole pilot was not aware of the helicopter’s presence and that an incident had occurred.

The ATSB also found that the helicopter operator's traffic alert and collision avoidance knowledge was inadequate with respect to resolution advisory alert terrain considerations and the required intensity of response manoeuvring.

What has been done as a result

The Seminole operator implemented a non-technical skills education program. This included situational awareness, potential biases, and the dangers of student-instructional distractions, particularly during periods of high workload.

The helicopter operator issued a safety alert to flight crew of TCAS equipped aircraft, alerting pilots to the ground inhibit functions of the system and the control response requirements for resolution advisory manoeuvres. The safety alert also highlights the mandatory compliance requirements of resolution advisories. 

The helicopter operator has also updated the flight crew training courseware, syllabus and simulator program for 2022. The updated simulator program incorporates elements relevant to the occurrence along with simulator instructor guides.

Safety message

This incident shows that the effective use of radio remains a primary defence in avoiding mid‑air collisions. This is achieved by maintaining an effective listening watch and proactive communication. The ATSB publication A pilot’s guide to staying safe in the vicinity of non-towered aerodromes highlights some of the known challenges presented to pilots operating around uncontrolled airfields.

The incident also highlighted the importance of effective flight crew TCAS training. TCAS is a complex system which serves as a ‘last line of defence’ in airborne collision avoidance. Thorough knowledge of the system is critical in ensuring that crews respond appropriately to TCAS resolution advisories.

The ATSB also strongly encourages the fitment of ADS‑B transmitting, receiving and display devices as they significantly assist the identification and avoidance of conflicting traffic. The continuous positional information ADS‑B provides can highlight a developing situation many minutes before it becomes hazardous – a significant improvement on both point‑in‑time radio traffic advice and ‘see‑and‑avoid’. The ATSB also notes that ADS‑B receivers, for pilots operating under both the instrument or visual flight rules, are currently available within Australia at low cost and can be used in aircraft without any additional regulatory approval or expense.

It is also important to recognise that ADS‑B IN cannot be relied upon to display all nearby traffic so effective use of radio remains a primary defence in avoiding mid‑air collisions. In that context pilots need to make all required broadcasts detailed in the Aeronautical Information Publication, even if there is no known traffic, and respond to broadcasts if a potential traffic conflict is identified.

Download Final report
[Download  PDF: 1.09MB]

The occurrence


Safety analysis


Safety issues and actions


Sources and submissions



The Australian Transport Safety Bureau (ATSB) is investigating a separation issue involving two aircraft, a Moorabbin Aviation Services PA-44-180 and a Babcock Mission Critical Services AW139 above Mangalore Airport, Victoria on 6 June 2021.

At 1556, the AW139 was flying southbound toward Mangalore at 3,100 feet above mean sea level. At the same time, the PA-44 was conducting a practice instrument approach to Mangalore. The PA-44 commenced a missed approach from below 3,000 feet in a northerly direction toward Mangalore and the pilot broadcast that the aircraft would climb to 3,900 feet. Shortly after the PA-44 began climbing, the pilot of the AW139 received a traffic collision and avoidance (TCAS) alert and manoeuvred the aircraft to increase separation between the two aircraft. Both flights continued without further incident.

The evidence collection phase of the investigation will include reviewing recorded communications, air traffic control surveillance data and weather information and interviews with the flight crews.

A final report will be released at the conclusion of the investigation. Should a critical safety issue be identified during the course of the investigation, the ATSB will immediately notify relevant parties so that appropriate safety action can be taken.

Safety Issue

Go to AO-2021-023-SI-01 -

Inadequate traffic alert and collision avoidance training

The helicopter operator's traffic alert and collision avoidance system knowledge was inadequate with respect to resolution advisory alert terrain considerations and the required intensity of response manoeuvring.

Safety issue details
Issue number: AO-2021-023-SI-01
Status: Closed – Adequately addressed
General details
Date: 06 June 2021   Investigation status: Completed  
Time: 1556 EST   Investigation level: Defined - click for an explanation of investigation levels  
Location   (show map): overhead Mangalore Aerodrome   Investigation phase: Final report: Dissemination  
State: Victoria   Occurrence type: ACAS warning  
Release date: 27 May 2022   Occurrence category: Incident  
Report status: Final   Highest injury level: None  

Aircraft 1 details

Aircraft 1 details
Aircraft model AW139  
Aircraft registration VH-YXH  
Serial number 31607  
Operator Babcock Mission Critical Services  
Type of operation Medical Transport  
Sector Helicopter  
Damage to aircraft Nil  
Departure point Yielema, Victoria  
Destination Royal Melbourne Hospital, Victoria  

Aircraft 2 details

Aircraft 2 details
Aircraft manufacturer Piper Aircraft Corp  
Aircraft model PA-44-180  
Aircraft registration VH-HMQ  
Serial number 44-7995201  
Operator Moorabbin Aviation Services  
Type of operation Flying Training  
Sector Piston  
Damage to aircraft Nil  
Departure point Wagga, Wagga, NSW  
Destination Mangalore, Victoria  
Last update 27 May 2022