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Summary

Summary

The flight plan track, which was an on-screen indication showing the location of the Boeing 767 (B767) aircraft while outside radar coverage, disappeared from the air situation display while the crew was receiving an air traffic control service. This loss of display resulted in the controller loosing situational awareness and no separation or SAR alerting service being provided to the aircraft.

The controller observed the aircraft's flight plan track overhead Oodnadatta at 1727 Central Summer Time. At 1736 the crew reported their position overhead AGAGO, the controller had no on-screen indication of the B767 as the flight data record for the aircraft no longer existed. All indications of the aircraft had been removed from the controller's screen.

An investigation carried out by Airservices Australia revealed that the crew of an aircraft close to Sydney was cycling through SSR codes on its transponder and momentarily squawked the code that was assigned to the flight data record of the aircraft near Oodnadatta. The received transponder return was a valid code within the coupling corridor associated with that aircraft's track. That scenario caused a false radar coupling that resulted in The Australian Advanced Air Traffic System (TAAATS) automatically modifying the flight data record; which resulted in the deletion of the flight plan track and the controller's jurisdiction strip. That sequence of events displayed a coupled radar track for 10 seconds. However, the track was outside of the controllers displayed range.

A flight data record may couple on either the Previous SSR code (PSSR) or Assigned SSR code (ASSR), there was no indication to the controller on which of these codes the flight data record had coupled unless the controller selected "SSR ALL" to determine the squawked code. The PSSR is the code assigned by the previous control authority, in the receiving control authority TAAATS attempts to retain this code. The aircraft PSSR was the code assigned by the Singapore Control Authority and was retained by Brisbane and Melbourne TAAATS. This code was one normally used for code allocations to Visual Flight Rules flight data records.

 
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