What happened
At about 0928 Central Australian Standard Time on 30 July 2024, a Cessna 208B aircraft, with a pilot and 11 passengers on board, departed William Creek aerodrome for a local sightseeing flight over Kati Thanda – Lake Eyre, South Australia. The aircraft was operating second in company with a lead 208B aircraft which had departed shortly before and was making positional radio calls along the route. Both aircraft tracked east to cross the lake shore at about 500 ft AGL, before turning north-east to follow the lake and the Warburton River towards Birdsville, Queensland.
At around the same time as the 208 aircraft departed William Creek, a Cessna T210N aircraft, with a pilot and 5 passengers on board, departed Birdsville aerodrome for a sightseeing flight following the Warburton River, towards the lake, at around the same altitude.
The lead 208 aircraft, which was equipped with ADS-B IN[1], had contacted the T210 as the aircraft flew toward each other, with the pilot of the following 208 reporting that they heard the communication and were aware of the T210.
Shortly after the second 208 passed Kalamurina (on the Warburton River), the pilot reported they saw the T210 and made an immediate right turn to ensure separation. The T210 pilot reported also seeing the 208 at the same time and made a similar immediate right turn. The 208 pilot estimated that the aircraft came within around 100 m horizontally, with the T210 passing approximately 20 to 30 m below the 208 as the aircraft crossed.
Both aircraft continued their flights and landed in their respective destinations. The 208 pilot reported discussing the event with the passengers and later contacting the T210 pilot to debrief the incident.
Safety action
The 208 operator conducted a documented review of the occurrence and reiterated with flight crew the need to use all available information to reinforce situational awareness, particularly when operating in traffic convergence areas over the lake. The use of prescribed VFR cruising altitudes[2] when transiting to and from the lake area below 3,000 ft was also recommended. Further, the operator indicated that ADS-B IN technology was scheduled for fitment to the incident aircraft during the next maintenance period.
The operators of both aircraft have also agreed and adopted a policy for east / west separated flightpaths when travelling to and from the lake, ensuring converging traffic will have lateral separation by default.
Safety message
The ATSB SafetyWatch program highlights the broad safety concerns that come out of our investigation findings and from the occurrence data reported to us by industry. One of the safety areas is encouraging the use of available technology to enhance safety.
In this instance, while all aircraft were equipped with Automatic Dependent Surveillance – Broadcast (ADS-B) systems, only the lead 208 utilised a system that received ADS-B transmissions and allowed the pilot to see the real-time positions of other aircraft in proximity (ADS-B IN). Had the following 208 and the T210 aircraft also been equipped with this capability, it is likely that coordination and maintenance of separation would have been achieved before the aircraft came into proximity.
Kati Thanda – Lake Eyre is a popular sightseeing destination with, at times, multiple smaller aircraft operating within the local broadcast zone. Operators and pilots of aircraft flying in this area should consider the limitations of the visual ‘see and avoid’ principle and utilise all available methods and technologies for ensuring safe aircraft separation.
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.
[1] An avionics system capable of receiving Automatic Dependent Surveillance – Broadcast data from other aircraft and displaying aircraft positional information to the crew.
[2] To ensure vertical separation for aircraft on converging tracks, CASR 91.275 requires that VFR aircraft fly at altitudes that are prescribed according to the aircraft’s east-oriented or west-oriented track.