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The ATSB's final investigation report into an airspace incident on 7 April involving a Boeing 737 and a Lancair aircraft has found that while it was an 'airprox' it was not a 'serious incident' because of timely action by the air traffic controller and both crews.

The Boeing 737, operating under the instrument flight rules (IFR), was en route from Townsville and descending for a landing at Brisbane. A Neico Lancair IV-P aircraft, operating under the visual flight rules (VFR), was en route from Maroochydore to St George, on climb to flight level (FL) 165.

Both aircraft were operating in Class E airspace when the 737 crew observed a TCAS traffic symbol and received subsequent TCAS alerts. This airspace was introduced as part of the National Airspace System (NAS) phase 2b from 27 November 2003.

Despite the assistance of air traffic control to both crews, the 737 crew had observed the Lancair's traffic symbol on the TCAS display but could not see the Lancair. They decreased the rate of descent and after receiving TCAS traffic advisory (TA) and resolution advisory (RA) alerts, climbed the 737 to FL166 and turned about 15 degrees right of track. Recorded Air Traffic Services (ATS) radar data indicated that the Lancair altered track 8 degrees to the right away from the 737 just before passing behind and below the 737. The minimum distance between the two aircraft was about 600 ft vertically at about 0.3 NM (about 556 metres) laterally.

Information obtained from the crews of each aircraft, the ATS controller, recorded flight data from the 737, ATS audio recordings and radar data, was consistent. Based on all of the circumstances, the incident was classified as an 'airprox' but not a 'serious incident'.

The investigation found that the crews of both aircraft and the air traffic controller complied with the published procedures for Class E airspace under NAS 2b.

Airservices Australia advised it had subsequently issued a national instruction and an information circular on safety alerts, traffic avoidance advice, and traffic information. It had also produced a computer-based training program for air traffic controllers on duty of care, which provided advice on when a safety alert is to be initiated.

The full investigation report 200401273.

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Last update 29 January 2014