On 27 May 2003, at about 1650 Western Standard Time, the pilot of a Cessna 172P (C172) aircraft, registered VH-AUC, was conducting circuits on runway 06 right (06R) at Jandakot. An instructor and student pilot of a Piper PA-38-112 (Tomahawk) aircraft, registered VH-FIG, were also conducting circuits on runway 06R.
While on downwind for runway 06R, the pilot of the C172 requested a landing on runway 06 left (06L). The aerodrome controller responsible for runway 06R (ADC1) acknowledged that request and instructed the pilot of the C172 to follow the Tomahawk, which was also on downwind for runway 06R. After coordinating with the aerodrome controller responsible for runway 06L (ADC2), the ADC1 cleared the pilot of the C172 to make an approach to runway 06L and instructed the pilot to transfer to the ADC2 frequency. The C172 subsequently passed in close proximity to the Tomahawk while the Tomahawk was on final for runway 06R and the C172 was on right base leg for runway 06L.
Radar data indicated that the crew of the Tomahawk had extended downwind for sequencing with a preceding aircraft and did not turn base for runway 06R until close to the control zone boundary. Radar data also indicated that the pilot of the C172 had turned right base for runway 06L from a late downwind position and had flown an oblique base leg to join final for runway 06L. Sun glare may have contributed to the C172 pilot losing sight of the Tomahawk ahead after it had turned onto the base leg.
The Tomahawk was at about 500 ft above ground level and descending on long final approach to runway 06R when the instructor observed the C172 tracking towards them. The instructor in the Tomahawk attempted to contact the pilot of the C172, but used the callsign of another aircraft believed to be operating in the circuit at the time and received no response. Regardless, the pilot of the C172 would not have heard any transmissions from the instructor, as the pilot was operating on a different frequency, as instructed by ADC1.
The Tomahawk instructor increased the rate of descent of the aircraft and monitored the position of the C172 before it passed directly overhead, left to right, about 50 ft above their aircraft. The instructor reported that the C172 was sighted approximately 20 seconds before it passed overhead. The C172 pilot was unaware of the incident until after landing when it was brought to his attention by the surface movement controller. Due to the distance from the control tower and the angle of observation, the aerodrome controllers could not accurately judge the relative positions between the aircraft on base and final approach.
Following this incident, Airservices Australia issued instructions to Jandakot aerodrome controllers to delay, where practicable, the transfer of aircraft onto another frequency when facilitating a change in landing runway.