At 0710 Western Standard Time, a Fokker F28‑100 (F100) aircraft, registered VH‑FKJ (FKJ), was approaching Karratha, Western Australia, on the 204 radial, 11 NM behind a Boeing 717 (B717).
At 0714, a Cessna 310R, registered VH‑AEY (AEY), departed Karratha on a VFR flight to Exmouth. During the climb, the Karratha tower controller instructed AEY to track to intercept the 180-radial outbound, to provide segregation with the inbound F100.
As FKJ was approaching 21 NM from Karratha and 7,000 ft on descent, the crew was cleared to make a visual approach and track direct to Karratha. FKJ was 10 NM behind the B717, which was conducting an approach to a 5 NM final for runway 08.
At 0718, the pilot of AEY was given the F100 as traffic, on approach to Karratha on the 204-radial at about 13 NM. The pilot of AEY replied that they had the traffic visual, in their 2 o’clock position. They were instructed by the controller to pass behind that aircraft and track direct to Exmouth. The pilot subsequently reported that they had sighted the B717, mistaken it for the F100, and turned to track to Exmouth.
At 0719, AEY appeared on the traffic collision avoidance system (TCAS) display in FKJ as proximity traffic. As AEY came within 5 NM on the TCAS display, the crew levelled the aircraft off at about 4,000 ft, as a precaution.
The TCAS then went from a proximity warning to a traffic advisory (TA). Neither of the crew sighted AEY, which was climbing and approaching 4,000 ft. The pilot of AEY made a visual scan and saw FKJ coming towards AEY in a 10 o’clock high position about 1 to 2 NM away. The pilot descended AEY about 200 ft as FKJ passed overhead. At 0720, the crew of FKJ received a TCAS resolution advisory (RA) climb instruction, which they complied with. The TCAS display showed AEY passed about 700 ft below FKJ.
The pilot of AEY reported that they had misidentified the B717 as the F100 and commented that if they had been given information on the B717, they may not have misidentified the traffic.