Incident Description
On June 9, 2021, at approximately 08:40 local time, an Aero AT3-R100 (registration SP-RWG) and a Cessna 152 (registration SP-KOG) were conducting training flights in the traffic pattern at EPBC airport, operating to runway 28L. Both aircraft had instructors on board. The Aero AT3 began another circuit, with the Cessna following behind, maintaining separation.
Sequence of Events
During the flight, another aircraft entered the traffic pattern from point VFR FOXTROT, heading toward the first turn. The instructor in the Aero AT3 misinterpreted the radio communication, believing the Cessna was joining behind him.
Around 08:44:30, the Aero AT3 was outside the second turn, which it completed about 20 seconds later, ending up approximately 1 km outside the published pattern. The Cessna crew assessed that the Aero AT3 was heading toward point LIMA, leaving the ATZ. Both aircraft were moving toward the third turn. The Cessna flew parallel to the downwind leg inside the pattern, while the Aero AT3 flew outside and approached the published track. The separation between the aircraft decreased significantly during the second turn and continued to diminish as they flew toward the third turn.
When on the downwind leg, the Aero AT3 crew heard the Cessna report its position. After checking the airspace, they spotted the Cessna to the right, slightly behind and about 100-150 ft below. The Aero AT3 instructor requested that the Cessna establish separation behind his aircraft. However, the Cessna instructor believed the Aero AT3 was behind. The instructors discussed the situation over the radio but continued flying without reaching an agreement. The Aero AT3 crew photographed the Cessna during the third turn.
Around 08:47, both aircraft executed the third turn, cutting it short. The Cessna, taking a shorter path in the pattern, overtook the Aero AT3. After the third turn, the Aero AT3 established separation behind the Cessna. Both aircraft continued without further incident.
Flight Path Analysis
Analysis of the Aero AT3's circuits showed that the leg from the first to the second turn and the second turn itself were outside the published pattern. The circuit in which the incident occurred deviated the most from the published track. The Cessna's circuits consistently cut the first, second, and third turns, shortening the path. The incident circuit was typical for the Cessna.
Both aircraft crews saw each other near the downwind position and heard position reports. Each crew believed their aircraft was ahead and had priority in the pattern. The instructors did not reach a consensus during their radio exchange and did not pass on practical knowledge about reducing the risk of air proximity hazards. The problem of insufficient separation was identifiable when crews reported the downwind position, and the escalating situation was evident from the instructors' exchanges. The flight director did not react to the situation.
Investigation Findings
The investigation identified the cause as improper analysis of the traffic situation in the traffic pattern. Contributing factors included: the Aero AT3 crew executing the second turn outside the published pattern; both crews losing situational awareness, leading to each believing they had priority; and the lack of response from the flight director to the potentially dangerous situation.
Preventive Actions
The incident was discussed at a logistics center conference (EPBC airport manager) and within both training organizations. The airport manager limited traffic in the pattern to six aircraft, with an average circuit time of about 9-10 minutes, to improve separation maintenance.