The traffic collision avoidance system (TCAS) on one of the two Qantas Airways Airbus A330s involved in a loss of separation incident in September was not working, early investigations have found.
Aircraft VH-EBO was operating a Sydney-Perth flight while aircraft VH-EBS, was on the Perth-Sydney route when the incident happened near Adelaide on 20 September.
The Australian Transport Safety Bureau (ATSB) says in a preliminary update that unlike pilots on aircraft EBS, the flight crew on aircraft EBO reported that they did not receive any indications on their TCAS display of the presence of another aircraft, neither did they get any traffic or resolution advisories.
The pilots added that they could not see other aircraft on their TCAS display during the rest of the flight until they reached the Perth terminal area. They had however been able to see other aircraft on display from Sydney and there had been no indication of a TCAS failure before the loss of separation event, adds the ATSB.
A full system test later found a failure between EBO’s ATC transponder 2 and the TCAS computer and antennas. Replacements of those parts corrected the errors.
The loss of separation happened when air traffic control approved EBO’s request to climb from 38,000ft (11,600m) to 40,000ft. The controller’s short term conflict alert system, however, was soon activated, alerting them to the imminent loss of separation between the two aircraft. The controller quickly instructed EBO to maintain at 38,000ft.
Recorded data showed that the two aircraft’s minimum vertical separation was 650ft, while the minimum lateral separation was 1.6nm (2.96km) when the aircraft were 870ft apart vertically.
The air traffic controllers reported that the workload was relatively low at the time of the incident and that there were no operational distractions.
The ATSB says it will conduct further analysis of the air traffic control radar and audio data, as well as recorded data from the two aircraft. It will also analyse the context in which the controller’s action occurred, and examine EBO’s TCAS computer and related components.
Investigations are expected to be completed by September 2014.