Collision alert sounded in student pilot, medical helicopter close call: ATSB

The incident, which occurred near Mangalore - between Shepparton in northern Victoria and Melbourne - has been under investigation by the Australian Transport Safety Bureau (ATSB) since June.

A student pilot in a Piper PA-44 Seminole - a twin-engine light plane - operated by Moorabbin Aviation Services and accompanied by an instructor took off from Wagga on an instrument flight rules training run on June 6, bound for Mangalore airport.

As the Seminole tracked north along a Mangalore runway, an AugustaWestland medical retrieval helicopter - operated by Babcock Mission Critical Services Australia - with crew on board transporting a patient to Royal Melbourne Hospital was set to pass over the airport at 3100 feet.

After descending, the Seminole instructor and student were unable to sight the runway due to cloud conditions and initiated a missed approach, intending to climb to 4000 feet and divert to Shepparton Airport.

The helicopter's traffic collision avoidance system [TCAS] alerted its pilot, who commanded the autopilot to begin climbing.

Another advisory issued by the system was then "incorrectly perceived ... as a descent instruction" by the pilot, who began turning away from the Seminole in a bid to avoid terrain and not change vertical course and startle those on board.

Six seconds later, the crafts passed while in cloud within 543 feet of each other, the ATSB said.

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No one was injured in the course of the incident and the plane student and instructor, who eventually landed at Shepparton, were unaware it had unfolded.

The helicopter pilot had been aware of the plane's presence, the ATSB said, however did not recognise its flight plan conflicted with the missed approach path.

Air traffic control shared the helicopter's traffic information to the Seminole, which was not interpreted correctly as it came at the same time the student asked the instructor a question. The instructor then was of the belief the advice related to a helicopter with a similar call sign that had been passed 15 minutes earlier.

The safety body handed down a final report this month, finding the helicopter pilot did not take into account the change that a missed approach by the Seminole could bring the aircraft closer together.

"The ATSB's investigation into this occurrence found that while the helicopter pilot was aware of the Seminole, they did not consider the possibility of the Seminole conducting a missed approach, which might conflict with the helicopter's flight path," ATSB director of transport safety Stuart Macleod said.

"The Seminole's pilot, meanwhile, reported not hearing broadcasts from the helicopter and misinterpreted traffic advice from air traffic control, and consequently was not aware of the helicopter nearby and that an incident had occurred."

The helicopter's TCAS knowledge was found to be inadequate with respect to resolution advisory alert terrain considerations and the required intensity of response manoeuvring, the ATSB said.

"As such, this incident highlights the importance of effective flight crew TCAS training," Mr Macleod said.

"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 incident also highlights the effectiveness of radio use as a primary defence in avoiding mid-air collisions in non-controlled airspace, the ATSB said.