The occurrence

On 28 November 2020, a Jetstar Airways Airbus A320-232 aircraft, registered VH-VGP (VGP), was conducting a regular public transport (RPT) flight from Melbourne Airport, Victoria, to Ballina Byron Gateway Airport (Ballina Airport), New South Wales (NSW). At about 1122 Eastern Daylight-saving Time,^[1] when VGP was approximately 40 NM to the south-west of Ballina Airport, the flight crew made a broadcast on the common traffic advisory frequency (CTAF).^[2] This CTAF is shared with two neighbouring airports and several neighbouring aircraft landing areas (ALAs) including Evans Head (Figure 1).

Figure 1: CTAF Airports

Source: Airservices Australia, annotated by the ATSB

On receipt of VGP’s broadcast, the Ballina Airport certified air/ground radio operator (CA/GRO) (see Certified air/ground radio service section) contacted the flight crew of VGP. The CA/GRO confirmed that the flight crew were aware of an RPT A320 aircraft departing to the south from runway 06 at Ballina Airport, and an RPT Boeing 737 inbound to Ballina Airport from the south.

At about the same time, a Jabiru J230D aircraft, registered 24-7456 (7456), was conducting a private visual flight rules flight from Heck Field ALA, Queensland, to Evans Head ALA, NSW. At 1124:49, the pilot of 7456 made a broadcast on the CTAF, addressed to Lismore traffic, advising that the aircraft was 4 NM to the east of Lismore at 5,300 feet and descending. The flight crew of VGP did not respond to, or recall hearing, this broadcast.

Meanwhile, VGP continued its track towards Ballina Airport via the waypoint^[3] ‘OPESO’, descending to an altitude of about 3,200 feet in preparation for the required navigation performance^[4] approach for runway 06. Prior to crossing the OPESO waypoint, the flight crew of VGP received a traffic collision avoidance system (TCAS) proximate traffic alert for an unidentified aircraft at an unspecified altitude in the 11 o’clock^[5] position relative to VGP (see Traffic collision avoidance system section). Unbeknown to the flight crew of VGP, the proximate traffic was probably 7456 tracking in a southerly direction towards Evans Head (Figure 2).

Figure 2: VH-VGP and 24-7456 tracks

Source: Google Earth, annotated by the ATSB

The pilot of 7456 had not heard the earlier CTAF broadcast from VGP and was unaware that the two aircraft were on converging tracks. 7456 was fitted with a transponder that could transmit the aircraft’s altitude. However, 7456’s transponder was selected ‘ON’ (not ALT) and was not transmitting the altitude of the aircraft (without the altitude information, the TCAS on board VGP could only display the relative horizontal position of 7456).

At that time, there was no cloud and visibility was greater than 10 km. The flight crew of VGP attempted, unsuccessfully, to visually acquire the proximate traffic, but did not attempt to contact the traffic on the CTAF.

At 1128:17, VGP’s flight crew received a TCAS traffic advisory. The flight crew maintained their visual scan and continued with the approach to runway 06.

At 1128:38, the flight crew of VGP made a broadcast on the shared CTAF and advised Ballina traffic, and the Boeing 737 aircraft in the vicinity, that VGP had just passed waypoint OPESO. The pilot of 7456 did not respond to, or recall hearing, this broadcast.

The data obtained from VGP’s quick access recorder and the OzRunways program used by the pilot of 7456, indicates that, at approximately 12 NM south west of Ballina Airport, the tracks of VGP and 7456 intersected, with vertical separation between the two aircraft reducing to about 600 feet. The flight crew of VGP sighted 7456 just prior to passing below the aircraft. The pilot of 7456 sighted VGP shortly after passing above the aircraft. Both the pilot of 7456 and the flight crew of VGP observed no lateral separation between the two aircraft (Figure 3).

Figure 3: Recorded flight paths of VH-VGP and 24-7456

Source: Google Earth, annotated by the ATSB

At 1128:59, the flight crew of VGP contacted the crew of the Boeing 737 inbound to Ballina Airport on the shared CTAF to advise that they had experienced a traffic advisory, and the involved aircraft was now headed in the direction of the Boeing 737.

A short time later, VGP landed at Ballina Airport while 7456 continued on to Evans Head ALA.

Context

Airspace

Ballina Airport is located within uncontrolled Class G airspace. Overlying this airspace is Class C controlled airspace with a base of 8,500 feet above mean sea level.

The airspace surrounding Ballina Airport is available for use by aircraft operating under visual flight rules and instrument flight rules with significant recreational and sport aviation activity in the area. Ballina Airport is also serviced by several low and high capacity regular public transport operators.

Common traffic advisory frequency

The Ballina Airport CTAF is a designated frequency on which pilots make positional broadcasts when operating in the vicinity of the airport. The Ballina Airport CTAF is shared with neighbouring airports and ALAs in order to aid with traffic coordination and enhance the situational awareness of pilots operating within the surrounding airspace.

Pilots are required to make a CTAF broadcast whenever it is reasonably necessary to do so to avoid a collision, or the risk of collision, with another aircraft. Recommended positional broadcasts are listed in the table below (Figure 4)

Figure 4: CTAF recommended positional broadcasts

Source: Civil Aviation Safety Authority, modified by the ATSB

Certified air/ground radio service

Ballina Airport is one of only two airports in Australia to have a certified air/ground radio service (CA/GRS) in operation. A CA/GRS is a radio information service that is operated at a non-controlled airport and is provided by the airport operator.

The Ballina Airport CA/GRS commenced operations in March 2017 in response to the increasing number of aircraft movements at the airport. The purpose of the service is to provide pilots with operational information relevant to the airport to aid with decision making. The information provided includes:

• frequency confirmation
• traffic information on first call
• airport weather
• other advice to facilitate aeronautical safety and efficiency.

At the time of the incident, the service was provided to all aircraft operating within a designated broadcast area of 10 NM, during RPT operations (greater than 30 seats) between the hours of 0800-1800 local time.

Traffic collision avoidance system

A traffic collision avoidance system, as fitted to VGP, interrogates the transponders^[6] of nearby aircraft and uses this information to calculate the relative range and altitude of this traffic. The system provides a visual representation of this information to the flight crew as well as issuing alerts should a traffic issue be identified. These alerts include:

• Proximate traffic – an alert issued when an aircraft is within a range of less than 6 NM and 1200 feet, or a range of 6 NM if the traffic is not transmitting altitude information.
• Traffic advisory (TA) – an alert issued when the detected traffic may result in a conflict. Pilots are expected to initiate a visual search for the traffic causing the TA.
• Resolution advisory (RA) – a manoeuvre, or a manoeuvre restriction, calculated by the TCAS to avoid a collision. Pilots are expected to respond immediately to an RA unless doing so would jeopardise the safe operation of the flight.

A TCAS cannot detect aircraft that are not equipped with a transponder. Additionally, the system is unable to issue a RA for traffic that is not fitted with an altitude reporting transponder (mode C or S), or in circumstances where the mode C or S transponder on board the conflicting traffic is not transmitting altitude information—as was the case with 7456.

Further investigation

The investigation is continuing and will include the examination of:

• airspace density levels
• airspace suitability
• flight crew actions
• CA/GRS procedural design and application
• future Ballina airspace plans
• TCAS and recorded flight data
• CTAF recordings.

Should a critical safety issue be identified during the course of the investigation, the ATSB will immediately notify relevant parties so appropriate and timely safety action can be taken.

A final report will be released at the conclusion of the investigation.

__________

1. Eastern Daylight-saving Time (EST): Universal Coordinated Time (UTC) +11 hours.
2. A common traffic advisory frequency is a designated frequency on which pilots make positional broadcasts when operating in the vicinity of a non-controlled airport or within a broadcast area.
3. A waypoint is a specified geographical location used to define an area navigation route or the flight path of an aircraft employing area navigation.
4. A statement of the navigation performance necessary for operation within a defined airspace.
5. The position of an object or location relative to the aircraft with 12 o'clock considered the dead-ahead position.
6. A transponder is a receiver/transmitter fitted to an aircraft which will generate a reply signal upon proper interrogation; the interrogation and reply being on different frequencies.

The ATSB is investigating a separation occurrence involving a Jetstar Airbus A320, registered VH-VGP, and a privately operated Jabiru J230-D, registered 24-7456, near Ballina Byron Gateway Airport, New South Wales (NSW), on 28 November 2020.

While the A320 was approaching runway 06 to land at Ballina Byron Gateway Airport, the J230D was tracking south toward Evans Head Airport, NSW. About 22 km south-west of Ballina Byron Gateway Airport, the two aircraft's flight paths intersected, resulting in the reported generation of a traffic collision avoidance system (TCAS) traffic advisory indication to the Jetstar crew. The A320 passed beneath the J230-D and continued to Ballina.

The evidence collection phase of the investigation will include reviewing recorded communications and flight data, and interviews with the flight crew.

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.