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Analysis

Summary

The information provided to the Alice Springs aerodrome controller, from both the pilot of the C310 and the crew of the 717, indicated that a lateral separation standard existed between the aircraft. On that basis, the aerodrome controller cleared the crew of the 717 to descend below the level of the C310. However, the position of the Cessna C310 relative to the 717, as reported by the 717 crew, at the time the aerodrome controller cleared the 717 crew to descend through the level of the C310, meant that no procedural separation standard existed between the two aircraft. The aerodrome controller had no indication that the information from either source may have been erroneous, before clearing the 717 to descend through the level of the C310. It was not possible for the investigation to determine why the lateral separation standard applied by the aerodrome controller was compromised.

The integrity of procedural separation standards relies on the accuracy of information provided to air traffic control by pilots. Once the pilot of the C310 reported that the aircraft was established in the training area, the aerodrome controller had established a lateral separation standard between the C310 and the 717. He was then able to clear the 717 to descend through the level of the C310. Pilots need to be mindful of the importance of the accuracy of the information they provide to air traffic control in maintaining the integrity of published separation standards.

 
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